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How can I convert part of an api response from an object to a list? [duplicate]

I'm trying to fix my SendGridPlus library to deal with SendGrid events, but I'm having some trouble with the inconsistent treatment of categories in the API.
In the following example payload taken from the SendGrid API reference, you'll notice that the category property for each item can either be a single string or an array of strings.
[
{
"email": "john.doe#sendgrid.com",
"timestamp": 1337966815,
"category": [
"newuser",
"transactional"
],
"event": "open"
},
{
"email": "jane.doe#sendgrid.com",
"timestamp": 1337966815,
"category": "olduser",
"event": "open"
}
]
It seems my options to make JSON.NET like this are fixing the string before it comes in, or configuring JSON.NET to accept the incorrect data. I'd rather not do any string parsing if I can get away with it.
Is there any other way I can handle this using Json.Net?

The best way to handle this situation is to use a custom JsonConverter.
Before we get to the converter, we'll need to define a class to deserialize the data into. For the Categories property that can vary between a single item and an array, define it as a List<string> and mark it with a [JsonConverter] attribute so that JSON.Net will know to use the custom converter for that property. I would also recommend using [JsonProperty] attributes so that the member properties can be given meaningful names independent of what is defined in the JSON.
class Item
{
[JsonProperty("email")]
public string Email { get; set; }
[JsonProperty("timestamp")]
public int Timestamp { get; set; }
[JsonProperty("event")]
public string Event { get; set; }
[JsonProperty("category")]
[JsonConverter(typeof(SingleOrArrayConverter<string>))]
public List<string> Categories { get; set; }
}
Here is how I would implement the converter. Notice I've made the converter generic so that it can be used with strings or other types of objects as needed.
class SingleOrArrayConverter<T> : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return (objectType == typeof(List<T>));
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
JToken token = JToken.Load(reader);
if (token.Type == JTokenType.Array)
{
return token.ToObject<List<T>>();
}
return new List<T> { token.ToObject<T>() };
}
public override bool CanWrite
{
get { return false; }
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
Here is an short program demonstrating the converter in action with your sample data:
class Program
{
static void Main(string[] args)
{
string json = #"
[
{
""email"": ""john.doe#sendgrid.com"",
""timestamp"": 1337966815,
""category"": [
""newuser"",
""transactional""
],
""event"": ""open""
},
{
""email"": ""jane.doe#sendgrid.com"",
""timestamp"": 1337966815,
""category"": ""olduser"",
""event"": ""open""
}
]";
List<Item> list = JsonConvert.DeserializeObject<List<Item>>(json);
foreach (Item obj in list)
{
Console.WriteLine("email: " + obj.Email);
Console.WriteLine("timestamp: " + obj.Timestamp);
Console.WriteLine("event: " + obj.Event);
Console.WriteLine("categories: " + string.Join(", ", obj.Categories));
Console.WriteLine();
}
}
}
And finally, here is the output of the above:
email: john.doe#sendgrid.com
timestamp: 1337966815
event: open
categories: newuser, transactional
email: jane.doe#sendgrid.com
timestamp: 1337966815
event: open
categories: olduser
Fiddle: https://dotnetfiddle.net/lERrmu
EDIT
If you need to go the other way, i.e. serialize, while keeping the same format, you can implement the WriteJson() method of the converter as shown below. (Be sure to remove the CanWrite override or change it to return true, or else WriteJson() will never be called.)
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
List<T> list = (List<T>)value;
if (list.Count == 1)
{
value = list[0];
}
serializer.Serialize(writer, value);
}
Fiddle: https://dotnetfiddle.net/XG3eRy

I was working on this for ages, and thanks to Brian for his answer.
All I am adding is the vb.net answer!:
Public Class SingleValueArrayConverter(Of T)
sometimes-array-and-sometimes-object
Inherits JsonConverter
Public Overrides Sub WriteJson(writer As JsonWriter, value As Object, serializer As JsonSerializer)
Throw New NotImplementedException()
End Sub
Public Overrides Function ReadJson(reader As JsonReader, objectType As Type, existingValue As Object, serializer As JsonSerializer) As Object
Dim retVal As Object = New [Object]()
If reader.TokenType = JsonToken.StartObject Then
Dim instance As T = DirectCast(serializer.Deserialize(reader, GetType(T)), T)
retVal = New List(Of T)() From { _
instance _
}
ElseIf reader.TokenType = JsonToken.StartArray Then
retVal = serializer.Deserialize(reader, objectType)
End If
Return retVal
End Function
Public Overrides Function CanConvert(objectType As Type) As Boolean
Return False
End Function
End Class
then in your class:
<JsonProperty(PropertyName:="JsonName)> _
<JsonConverter(GetType(SingleValueArrayConverter(Of YourObject)))> _
Public Property YourLocalName As List(Of YourObject)
Hope this saves you some time

As a minor variation to the great answer by Brian Rogers, here are two tweaked versions of SingleOrArrayConverter<T>.
Firstly, here is a version that works for all List<T> for every type T that is not itself a collection:
public class SingleOrArrayListConverter : JsonConverter
{
// Adapted from this answer https://stackoverflow.com/a/18997172
// to https://stackoverflow.com/questions/18994685/how-to-handle-both-a-single-item-and-an-array-for-the-same-property-using-json-n
// by Brian Rogers https://stackoverflow.com/users/10263/brian-rogers
readonly bool canWrite;
readonly IContractResolver resolver;
public SingleOrArrayListConverter() : this(false) { }
public SingleOrArrayListConverter(bool canWrite) : this(canWrite, null) { }
public SingleOrArrayListConverter(bool canWrite, IContractResolver resolver)
{
this.canWrite = canWrite;
// Use the global default resolver if none is passed in.
this.resolver = resolver ?? new JsonSerializer().ContractResolver;
}
static bool CanConvert(Type objectType, IContractResolver resolver)
{
Type itemType;
JsonArrayContract contract;
return CanConvert(objectType, resolver, out itemType, out contract);
}
static bool CanConvert(Type objectType, IContractResolver resolver, out Type itemType, out JsonArrayContract contract)
{
if ((itemType = objectType.GetListItemType()) == null)
{
itemType = null;
contract = null;
return false;
}
// Ensure that [JsonObject] is not applied to the type.
if ((contract = resolver.ResolveContract(objectType) as JsonArrayContract) == null)
return false;
var itemContract = resolver.ResolveContract(itemType);
// Not implemented for jagged arrays.
if (itemContract is JsonArrayContract)
return false;
return true;
}
public override bool CanConvert(Type objectType) { return CanConvert(objectType, resolver); }
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
Type itemType;
JsonArrayContract contract;
if (!CanConvert(objectType, serializer.ContractResolver, out itemType, out contract))
throw new JsonSerializationException(string.Format("Invalid type for {0}: {1}", GetType(), objectType));
if (reader.MoveToContent().TokenType == JsonToken.Null)
return null;
var list = (IList)(existingValue ?? contract.DefaultCreator());
if (reader.TokenType == JsonToken.StartArray)
serializer.Populate(reader, list);
else
// Here we take advantage of the fact that List<T> implements IList to avoid having to use reflection to call the generic Add<T> method.
list.Add(serializer.Deserialize(reader, itemType));
return list;
}
public override bool CanWrite { get { return canWrite; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var list = value as ICollection;
if (list == null)
throw new JsonSerializationException(string.Format("Invalid type for {0}: {1}", GetType(), value.GetType()));
// Here we take advantage of the fact that List<T> implements IList to avoid having to use reflection to call the generic Count method.
if (list.Count == 1)
{
foreach (var item in list)
{
serializer.Serialize(writer, item);
break;
}
}
else
{
writer.WriteStartArray();
foreach (var item in list)
serializer.Serialize(writer, item);
writer.WriteEndArray();
}
}
}
public static partial class JsonExtensions
{
public static JsonReader MoveToContent(this JsonReader reader)
{
while ((reader.TokenType == JsonToken.Comment || reader.TokenType == JsonToken.None) && reader.Read())
;
return reader;
}
internal static Type GetListItemType(this Type type)
{
// Quick reject for performance
if (type.IsPrimitive || type.IsArray || type == typeof(string))
return null;
while (type != null)
{
if (type.IsGenericType)
{
var genType = type.GetGenericTypeDefinition();
if (genType == typeof(List<>))
return type.GetGenericArguments()[0];
}
type = type.BaseType;
}
return null;
}
}
It can be used as follows:
var settings = new JsonSerializerSettings
{
// Pass true if you want single-item lists to be reserialized as single items
Converters = { new SingleOrArrayListConverter(true) },
};
var list = JsonConvert.DeserializeObject<List<Item>>(json, settings);
Notes:
The converter avoids the need to pre-load the entire JSON value into memory as a JToken hierarchy.
The converter does not apply to lists whose items are also serialized as collections, e.g. List<string []>
The Boolean canWrite argument passed to the constructor controls whether to re-serialize single-element lists as JSON values or as JSON arrays.
The converter's ReadJson() uses the existingValue if pre-allocated so as to support populating of get-only list members.
Secondly, here is a version that works with other generic collections such as ObservableCollection<T>:
public class SingleOrArrayCollectionConverter<TCollection, TItem> : JsonConverter
where TCollection : ICollection<TItem>
{
// Adapted from this answer https://stackoverflow.com/a/18997172
// to https://stackoverflow.com/questions/18994685/how-to-handle-both-a-single-item-and-an-array-for-the-same-property-using-json-n
// by Brian Rogers https://stackoverflow.com/users/10263/brian-rogers
readonly bool canWrite;
public SingleOrArrayCollectionConverter() : this(false) { }
public SingleOrArrayCollectionConverter(bool canWrite) { this.canWrite = canWrite; }
public override bool CanConvert(Type objectType)
{
return typeof(TCollection).IsAssignableFrom(objectType);
}
static void ValidateItemContract(IContractResolver resolver)
{
var itemContract = resolver.ResolveContract(typeof(TItem));
if (itemContract is JsonArrayContract)
throw new JsonSerializationException(string.Format("Item contract type {0} not supported.", itemContract));
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
ValidateItemContract(serializer.ContractResolver);
if (reader.MoveToContent().TokenType == JsonToken.Null)
return null;
var list = (ICollection<TItem>)(existingValue ?? serializer.ContractResolver.ResolveContract(objectType).DefaultCreator());
if (reader.TokenType == JsonToken.StartArray)
serializer.Populate(reader, list);
else
list.Add(serializer.Deserialize<TItem>(reader));
return list;
}
public override bool CanWrite { get { return canWrite; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
ValidateItemContract(serializer.ContractResolver);
var list = value as ICollection<TItem>;
if (list == null)
throw new JsonSerializationException(string.Format("Invalid type for {0}: {1}", GetType(), value.GetType()));
if (list.Count == 1)
{
foreach (var item in list)
{
serializer.Serialize(writer, item);
break;
}
}
else
{
writer.WriteStartArray();
foreach (var item in list)
serializer.Serialize(writer, item);
writer.WriteEndArray();
}
}
}
Then, if your model is using, say, an ObservableCollection<T> for some T, you could apply it as follows:
class Item
{
public string Email { get; set; }
public int Timestamp { get; set; }
public string Event { get; set; }
[JsonConverter(typeof(SingleOrArrayCollectionConverter<ObservableCollection<string>, string>))]
public ObservableCollection<string> Category { get; set; }
}
Notes:
In addition to the notes and restrictions for SingleOrArrayListConverter, the TCollection type must be read/write and have a parameterless constructor.
Demo fiddle with basic unit tests here.

To handle this you have to use a custom JsonConverter. But you probably already had that in mind.
You are just looking for a converter that you can use immediately. And this offers more than just a solution for the situation described.
I give an example with the question asked.
How to use my converter:
Place a JsonConverter Attribute above the property. JsonConverter(typeof(SafeCollectionConverter))
public class SendGridEvent
{
[JsonProperty("email")]
public string Email { get; set; }
[JsonProperty("timestamp")]
public long Timestamp { get; set; }
[JsonProperty("category"), JsonConverter(typeof(SafeCollectionConverter))]
public string[] Category { get; set; }
[JsonProperty("event")]
public string Event { get; set; }
}
And this is my converter:
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System;
namespace stackoverflow.question18994685
{
public class SafeCollectionConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return true;
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
//This not works for Populate (on existingValue)
return serializer.Deserialize<JToken>(reader).ToObjectCollectionSafe(objectType, serializer);
}
public override bool CanWrite => false;
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
}
And this converter uses the following class:
using System;
namespace Newtonsoft.Json.Linq
{
public static class SafeJsonConvertExtensions
{
public static object ToObjectCollectionSafe(this JToken jToken, Type objectType)
{
return ToObjectCollectionSafe(jToken, objectType, JsonSerializer.CreateDefault());
}
public static object ToObjectCollectionSafe(this JToken jToken, Type objectType, JsonSerializer jsonSerializer)
{
var expectArray = typeof(System.Collections.IEnumerable).IsAssignableFrom(objectType);
if (jToken is JArray jArray)
{
if (!expectArray)
{
//to object via singel
if (jArray.Count == 0)
return JValue.CreateNull().ToObject(objectType, jsonSerializer);
if (jArray.Count == 1)
return jArray.First.ToObject(objectType, jsonSerializer);
}
}
else if (expectArray)
{
//to object via JArray
return new JArray(jToken).ToObject(objectType, jsonSerializer);
}
return jToken.ToObject(objectType, jsonSerializer);
}
public static T ToObjectCollectionSafe<T>(this JToken jToken)
{
return (T)ToObjectCollectionSafe(jToken, typeof(T));
}
public static T ToObjectCollectionSafe<T>(this JToken jToken, JsonSerializer jsonSerializer)
{
return (T)ToObjectCollectionSafe(jToken, typeof(T), jsonSerializer);
}
}
}
What does it do exactly?
If you place the converter attribute the converter will be used for this property. You can use it on a normal object if you expect a json array with 1 or no result. Or you use it on an IEnumerable where you expect a json object or json array. (Know that an array -object[]- is an IEnumerable)
A disadvantage is that this converter can only be placed above a property because he thinks he can convert everything. And be warned. A string is also an IEnumerable.
And it offers more than an answer to the question:
If you search for something by id you know that you will get an array back with one or no result.
The ToObjectCollectionSafe<TResult>() method can handle that for you.
This is usable for Single Result vs Array using JSON.net
and handle both a single item and an array for the same property
and can convert an array to a single object.
I made this for REST requests on a server with a filter that returned one result in an array but wanted to get the result back as a single object in my code. And also for a OData result response with expanded result with one item in an array.
Have fun with it.

Just wanted to add to #dbc excellent response above on the SingleOrArrayCollectionConverter. I was able to modify it to use with a stream from an HTTP client. Here is a snippet (you will have to set up the requestUrl (string) and the httpClient (using System.Net.Http;).
public async Task<IList<T>> HttpRequest<T>(HttpClient httpClient, string requestedUrl, CancellationToken cancellationToken)
{
using (var request = new HttpRequestMessage(HttpMethod.Get, requestedUrl))
using (var httpResponseMessage = await httpClient.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, cancellationToken))
{
if (httpResponseMessage.IsSuccessStatusCode)
{
using var stream = await httpResponseMessage.Content.ReadAsStreamAsync();
using var streamReader = new StreamReader(stream);
using var jsonTextReader = new JsonTextReader(streamReader );
var settings = new JsonSerializerSettings
{
// Pass true if you want single-item lists to be reserialized as single items
Converters = { new SingleOrArrayCollectionConverter(true) },
};
var jsonSerializer = JsonSerializer.Create(settings);
return jsonSerializer.Deserialize<List<T>>(jsonTextReader);
}
I apologize if there are missing brackets or misspellings, it was not easy to paste code in here.

I had a very similar Problem.
My Json Request was completly unknown for me.
I only knew.
There will be an objectId in it and some anonym key value pairs AND arrays.
I used it for an EAV Model i did:
My JSON Request:
{objectId": 2,
"firstName": "Hans",
"email" :[ "a#b.de","a#c.de"],
"name": "Andre",
"something" :["232","123"]
}
My Class i defined:
[JsonConverter(typeof(AnonyObjectConverter))]
public class AnonymObject
{
public AnonymObject()
{
fields = new Dictionary<string, string>();
list = new List<string>();
}
public string objectid { get; set; }
public Dictionary<string, string> fields { get; set; }
public List<string> list { get; set; }
}
and now that i want to deserialize unknown attributes with its value and arrays in it my Converter looks like that:
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
AnonymObject anonym = existingValue as AnonymObject ?? new AnonymObject();
bool isList = false;
StringBuilder listValues = new StringBuilder();
while (reader.Read())
{
if (reader.TokenType == JsonToken.EndObject) continue;
if (isList)
{
while (reader.TokenType != JsonToken.EndArray)
{
listValues.Append(reader.Value.ToString() + ", ");
reader.Read();
}
anonym.list.Add(listValues.ToString());
isList = false;
continue;
}
var value = reader.Value.ToString();
switch (value.ToLower())
{
case "objectid":
anonym.objectid = reader.ReadAsString();
break;
default:
string val;
reader.Read();
if(reader.TokenType == JsonToken.StartArray)
{
isList = true;
val = "ValueDummyForEAV";
}
else
{
val = reader.Value.ToString();
}
try
{
anonym.fields.Add(value, val);
}
catch(ArgumentException e)
{
throw new ArgumentException("Multiple Attribute found");
}
break;
}
}
return anonym;
}
So now everytime i get an AnonymObject i can iterate through the Dictionary and everytime there is my Flag "ValueDummyForEAV" i switch to the list, read the first line and split the values. After that i delete the first entry from the list and go on with iteration from the Dictionary.
Maybe someone has the same problem and can use this :)
Regards
Andre

You can use a JSONConverterAttribute as found here: http://james.newtonking.com/projects/json/help/
Presuming you have a class that looks like
public class RootObject
{
public string email { get; set; }
public int timestamp { get; set; }
public string smtpid { get; set; }
public string #event { get; set; }
public string category[] { get; set; }
}
You'd decorate the category property as seen here:
[JsonConverter(typeof(SendGridCategoryConverter))]
public string category { get; set; }
public class SendGridCategoryConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return true; // add your own logic
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
// do work here to handle returning the array regardless of the number of objects in
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
// Left as an exercise to the reader :)
throw new NotImplementedException();
}
}

You don't need any custom converters, in this case I am usually creating a very simple JsonConstructor
public partial class Item
{
// ... all class properties
[JsonConstructor]
public Item(JToken category)
{
if (category.GetType().Name == "JArray")
Category = category.ToObject<List<string>>();
else
Category = new List<string> { category.ToString() };
}
public Item() { }
}
after this you can deserialize your json using common code
List<Item> items = JsonConvert.DeserializeObject<List<Item>>(json);

I found another solution that can handle the category as string or array by using object. This way I don´t need to mess up with the json serializer.
Please give it a look if you have the time and tell me what you think. https://github.com/MarcelloCarreira/sendgrid-csharp-eventwebhook
It´s based on the solution at https://sendgrid.com/blog/tracking-email-using-azure-sendgrid-event-webhook-part-1/ but I also added date conversion from timestamp, upgraded the variables to reflect current SendGrid model (and made categories work).
I also created a handler with basic auth as option. See the ashx files and the examples.
Thank you!

Newtonsoft JsonConverter to convert a string or object to object

I have a requirement for some deserialization I'm trying to handle where I could have these potential inputs:
{
"value": "a string"
}
-- or --
{
"value": {
"text": "a string"
// there are other properties, but for successful deserialization I only need text present
}
}
And I expect it to be able to successfully convert to the object, MyObject:
public class MyObject
{
[JsonProperty("text")
public string Text { get; set; }
}
So far this is what I have in my converter. This case works fine when it's a string (although not very efficient because I'm throwing an exception to catch a failed deserialization). However, when it's an object the reader throws an exception and I'm uncertain of how to handle it.
public class MyObjectConverter : JsonConverter
{
public override bool CanWrite { get => false; }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
public override bool CanConvert(Type objectType)
{
return objectType == typeof(string) || objectType == typeof(MyObject);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
var value = reader.Value?.ToString();
if (string.IsNullOrWhiteSpace(value))
{
return null;
}
try
{
return JObject.Parse(value).ToObject<MyObject>();
}
catch (Exception)
{
return new MyObject
{
Text = value
};
}
}
}
perhaps I'm there is already a nice way to do this that I'm unaware of? If not, how can I determine whether my input is a string or an object to be able to return the object I care about?
SOLUTION:
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (reader.TokenType == JsonToken.String)
{
return new MyObject
{
Text = reader.Value?.ToString()
};
}
else if (reader.TokenType == JsonToken.StartObject)
{
JObject obj = JObject.Load(reader);
return obj.ToObject<MyObject>();
}
else
{
return null;
}
}

Your Object isn't structured like the input your expecting. For the second case, MyObject would need to look like this:
// this is ugly
public class MyObject
{
public Value value{get;set;}
public class Value{
public string text {get;set;}
}
}
If you want to have just an object with a single Text property like you currently do, you could do something like this:
public override object ReadJson(JsonReader reader, Type objectType, object
existingValue, JsonSerializer serializer)
{
JObject obj = JObject.Load(reader);
var value = obj["value"];
if(value is JObject) // this will be true if the value property is a nested structure
return new MyObject(){Text=value["text"]}; // could also do value.ToObject<MyObject>() if you need more properties
else
return new MyObject(){Text=value};
}

Deserialize inconsistent JSON property

Hopefully someone can help me with the following inconsistency occurring in a large JSON file that I am attempting to deserialize using Newtonsoft.Json.
One of the properties of the object occasionally appears as:
"roles": [
{
"field1" : "value",
"field2" : "value"
}
]
While other times that same property appears as:
"roles": {
"roles": [
{
"field1" : "value",
"field2" : "value"
}
]
}
For reference, this property is implemented in its class as:
[JsonProperty("roles")]
public List<Role> Roles { get; set; }
What I need to happen is that whenever the second situation above occurs, the object contents are deserialized like the first situation. i.e. the "outer" object is discarded/ignored
I have managed to handle another inconsistency in this file when a separate property sometimes occurs as an object and sometimes as an array using the following approach in its class definition:
[JsonConverter(typeof(SingleValueArrayConverter<Address>))]
public List<Address> Location { get; set; }
And implemented as:
public class SingleValueArrayConverter<T> : JsonConverter
{
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
object retVal = new Object();
if (reader.TokenType == JsonToken.StartObject)
{
T instance = (T)serializer.Deserialize(reader, typeof(T));
retVal = new List<T>() { instance };
}
else if (reader.TokenType == JsonToken.StartArray)
{
retVal = serializer.Deserialize(reader, objectType);
}
return retVal;
}
public override bool CanConvert(Type objectType)
{
return true;
}
}
However, I am unable to work out this issue.
Can anyone help?

You can handle this inconsistency with a JsonConverter also. It will be a little different than the one you have, but the idea is very similar:
public class ArrayOrWrappedArrayConverter<T> : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return typeof(List<T>).IsAssignableFrom(objectType);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
JToken token = JToken.Load(reader);
if (token.Type == JTokenType.Array)
{
return CreateListFromJArray((JArray)token, serializer);
}
if (token.Type == JTokenType.Object)
{
JObject wrapper = (JObject)token;
JProperty prop = wrapper.Properties().FirstOrDefault();
if (prop.Value.Type == JTokenType.Array)
{
return CreateListFromJArray((JArray)prop.Value, serializer);
}
}
// If the JSON is not what we expect, just return an empty list.
// (Could return null or throw an exception here instead if desired.)
return new List<T>();
}
private List<T> CreateListFromJArray(JArray array, JsonSerializer serializer)
{
List<T> list = new List<T>();
serializer.Populate(array.CreateReader(), list);
return list;
}
public override bool CanWrite => false;
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
Then just add the converter to your Roles property and you should be good to go:
[JsonProperty("roles")]
[JsonConverter(typeof(ArrayOrWrappedArrayConverter<Role>))]
public List<Role> Roles { get; set; }
Working demo: https://dotnetfiddle.net/F6qgQB

the easiest way (not necessarily the cleanest) would be to manually alter the string before deserialising -
jsonString = jsonString.replace("\"roles\": {", "\"rolesContainer\": {");
jsonString = jsonString.replace("\"roles\":{", "\"rolesContainer\": {");
and then in your main code you would have both rolesContainer and roles as fields - and then merge them after
public List<Role> roles { get; set; }
public RoleContainer rolesContainer { get; set; }
public class RoleContainer {
Public List<Role> roles;
}
it's dirty, but it should work

How to fix InvalidCastException while using JsonConverter for an IList of Interfaces?

I am trying to create an abstraction layer for Json.NET deserialization using interfaces.
To achieve this I use custom JsonConverter which works just fine, until interfaces are introduced.
Following exception is thrown:
Unhandled Exception: Newtonsoft.Json.JsonSerializationException: Error
setting value to 'Items' on 'BatchList'. --->
System.InvalidCastException: Unable to cast object of type
'System.Collections.Generic.List1[BatchItems]' to type
'System.Collections.Generic.List`1[IBatchItems]
This is the setup to repro in a console app:
class Program
{
static void Main(string[] args)
{
var jsonBatch = #"{'items': [{'Id': 'name1','info': {'age': '20'}},{'Id': 'name2','info': {'age': '21'}}]}";
DeserializeAndPost(jsonBatch);
}
public static void DeserializeAndPost(string json)
{
IBatchList req;
req = JsonConvert.DeserializeObject<BatchList>(json);
Post(req);
}
public static void Post(IBatchList batchList)
{
Console.WriteLine(batchList.Items.FirstOrDefault().Id);
}
}
public interface IBatchList
{
List<IBatchItems> Items { get; set; }
}
public interface IBatchItems
{
string Id { get; set; }
JObject Info { get; set; }
}
[JsonObject(MemberSerialization.OptIn)]
public class BatchList : IBatchList
{
[JsonProperty(PropertyName = "Items", Required = Required.Always)]
[JsonConverter(typeof(SingleOrArrayConverter<BatchItems>))]
public List<IBatchItems> Items { get; set; }
}
[JsonObject]
public class BatchItems : IBatchItems
{
[JsonProperty(PropertyName = "Id", Required = Required.Always)]
public string Id { get; set; }
[JsonProperty(PropertyName = "Info", Required = Required.Always)]
public JObject Info { get; set; }
}
// JsonConverter
public class SingleOrArrayConverter<T> : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return (objectType == typeof(List<T>));
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
JToken token = JToken.Load(reader);
if (token.Type == JTokenType.Array)
{
return token.ToObject<List<T>>();
}
return new List<T> { token.ToObject<T>() };
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
List<T> list = (List<T>)value;
if (list.Count == 1)
{
value = list[0];
}
serializer.Serialize(writer, value);
}
public override bool CanWrite
{
get { return true; }
}
}
I expect the output to be deserialized JSON as I provide the type for the interface to be used for deserialization:
[JsonConverter(typeof(SingleOrArrayConverter<BatchItems>))]
to be used.
Instead, unhandled cast exception is being thrown.
Note that if I use instead SingleOrArrayConverter<IBatchItems>, I will get an exception
Newtonsoft.Json.JsonSerializationException: Could not create an instance of type
as the [JsonConverter(typeof(SingleOrArrayConverter<BatchItems>))] is meant to provide concrete type for the following interface: public List<IBatchItems> Items { get; set; }.

What you need to do is to combine the functionality of the following two converters:
SingleOrArrayConverter from this answer to How to handle both a single item and an array for the same property using JSON.net by Brian Rogers.
This converter handles the frequently-encountered case where a one-item collection is not serialized as a collection; you are already using this converter.
ConcreteConverter<IInterface, TConcrete> from this answer to How to deserialize collection of interfaces when concrete classes contains other interfaces.
This converter deserializes a declared interface (here IBatchItems) into a specified concrete type (here BatchItems). This is required because IList<T> is not covariant and thus an IList<BatchItems> cannot be assigned to a IList<IBatchItems> as you are currently trying to do.
The best way to combine these two converters is to adopt the decorator pattern and enhance SingleOrArrayConverter to encapsulate a converter for each of the list's items inside the list converter:
public class SingleOrArrayListItemConverter<TItem> : JsonConverter
{
// Adapted from the answers to https://stackoverflow.com/questions/18994685/how-to-handle-both-a-single-item-and-an-array-for-the-same-property-using-json-n
// By Brian Rogers, dbc et. al.
readonly JsonConverter itemConverter;
readonly bool canWrite;
public SingleOrArrayListItemConverter(Type itemConverterType) : this(itemConverterType, true) { }
public SingleOrArrayListItemConverter(Type itemConverterType, bool canWrite)
{
this.itemConverter = (JsonConverter)Activator.CreateInstance(itemConverterType);
this.canWrite = canWrite;
}
public override bool CanConvert(Type objectType)
{
return typeof(List<TItem>).IsAssignableFrom(objectType);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (reader.MoveToContent().TokenType == JsonToken.Null)
return null;
var contract = serializer.ContractResolver.ResolveContract(objectType);
var list = (ICollection<TItem>)(existingValue ?? contract.DefaultCreator());
if (reader.TokenType != JsonToken.StartArray)
{
list.Add(ReadItem(reader, serializer));
return list;
}
else
{
while (reader.ReadToContent())
{
switch (reader.TokenType)
{
case JsonToken.EndArray:
return list;
default:
list.Add(ReadItem(reader, serializer));
break;
}
}
// Should not come here.
throw new JsonSerializationException("Unclosed array at path: " + reader.Path);
}
}
TItem ReadItem(JsonReader reader, JsonSerializer serializer)
{
if (itemConverter.CanRead)
return (TItem)itemConverter.ReadJson(reader, typeof(TItem), default(TItem), serializer);
else
return serializer.Deserialize<TItem>(reader);
}
public override bool CanWrite { get { return canWrite; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var list = value as ICollection<TItem>;
if (list == null)
throw new JsonSerializationException(string.Format("Invalid type for {0}: {1}", GetType(), value.GetType()));
if (list.Count == 1)
{
foreach (var item in list)
WriteItem(writer, item, serializer);
}
else
{
writer.WriteStartArray();
foreach (var item in list)
WriteItem(writer, item, serializer);
writer.WriteEndArray();
}
}
void WriteItem(JsonWriter writer, TItem value, JsonSerializer serializer)
{
if (itemConverter.CanWrite)
itemConverter.WriteJson(writer, value, serializer);
else
serializer.Serialize(writer, value);
}
}
public class ConcreteConverter<IInterface, TConcrete> : JsonConverter where TConcrete : IInterface
{
//Taken from the answer to https://stackoverflow.com/questions/47939878/how-to-deserialize-collection-of-interfaces-when-concrete-classes-contains-other
// by dbc
public override bool CanConvert(Type objectType)
{
return typeof(IInterface) == objectType;
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
return serializer.Deserialize<TConcrete>(reader);
}
public override bool CanWrite { get { return false; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
public static partial class JsonExtensions
{
public static JsonReader MoveToContent(this JsonReader reader)
{
if (reader.TokenType == JsonToken.None)
reader.Read();
while (reader.TokenType == JsonToken.Comment && reader.Read())
;
return reader;
}
public static bool ReadToContent(this JsonReader reader)
{
if (!reader.Read())
return false;
while (reader.TokenType == JsonToken.Comment)
if (!reader.Read())
return false;
return true;
}
}
Then apply it as follows:
[JsonObject(MemberSerialization.OptIn)]
public class BatchList : IBatchList
{
[JsonProperty(PropertyName = "Items", Required = Required.Always)]
[JsonConverter(typeof(SingleOrArrayListItemConverter<IBatchItems>), typeof(ConcreteConverter<IBatchItems, BatchItems>))]
public List<IBatchItems> Items { get; set; }
}
Notes:
This version of SingleOrArrayListItemConverter<TItem> avoids pre-loading the entire array into a JToken hierarchy which may improve performance.
If IBatchItems later becomes polymorphic, you could replace ConcreteConverter with a converter that intelligently selects the concrete type to use based on the properties present as shown in e.g. the answers to Deserializing polymorphic json classes without type information using json.net and How to implement custom JsonConverter in JSON.NET to deserialize a List of base class objects?.
Demo fiddle here.

C# JsonConvert.DeserializeObject failing as JSON data sometimes contains an array and sometimes does not [duplicate]

I'm trying to fix my SendGridPlus library to deal with SendGrid events, but I'm having some trouble with the inconsistent treatment of categories in the API.
In the following example payload taken from the SendGrid API reference, you'll notice that the category property for each item can either be a single string or an array of strings.
[
{
"email": "john.doe#sendgrid.com",
"timestamp": 1337966815,
"category": [
"newuser",
"transactional"
],
"event": "open"
},
{
"email": "jane.doe#sendgrid.com",
"timestamp": 1337966815,
"category": "olduser",
"event": "open"
}
]
It seems my options to make JSON.NET like this are fixing the string before it comes in, or configuring JSON.NET to accept the incorrect data. I'd rather not do any string parsing if I can get away with it.
Is there any other way I can handle this using Json.Net?

The best way to handle this situation is to use a custom JsonConverter.
Before we get to the converter, we'll need to define a class to deserialize the data into. For the Categories property that can vary between a single item and an array, define it as a List<string> and mark it with a [JsonConverter] attribute so that JSON.Net will know to use the custom converter for that property. I would also recommend using [JsonProperty] attributes so that the member properties can be given meaningful names independent of what is defined in the JSON.
class Item
{
[JsonProperty("email")]
public string Email { get; set; }
[JsonProperty("timestamp")]
public int Timestamp { get; set; }
[JsonProperty("event")]
public string Event { get; set; }
[JsonProperty("category")]
[JsonConverter(typeof(SingleOrArrayConverter<string>))]
public List<string> Categories { get; set; }
}
Here is how I would implement the converter. Notice I've made the converter generic so that it can be used with strings or other types of objects as needed.
class SingleOrArrayConverter<T> : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return (objectType == typeof(List<T>));
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
JToken token = JToken.Load(reader);
if (token.Type == JTokenType.Array)
{
return token.ToObject<List<T>>();
}
return new List<T> { token.ToObject<T>() };
}
public override bool CanWrite
{
get { return false; }
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
Here is an short program demonstrating the converter in action with your sample data:
class Program
{
static void Main(string[] args)
{
string json = #"
[
{
""email"": ""john.doe#sendgrid.com"",
""timestamp"": 1337966815,
""category"": [
""newuser"",
""transactional""
],
""event"": ""open""
},
{
""email"": ""jane.doe#sendgrid.com"",
""timestamp"": 1337966815,
""category"": ""olduser"",
""event"": ""open""
}
]";
List<Item> list = JsonConvert.DeserializeObject<List<Item>>(json);
foreach (Item obj in list)
{
Console.WriteLine("email: " + obj.Email);
Console.WriteLine("timestamp: " + obj.Timestamp);
Console.WriteLine("event: " + obj.Event);
Console.WriteLine("categories: " + string.Join(", ", obj.Categories));
Console.WriteLine();
}
}
}
And finally, here is the output of the above:
email: john.doe#sendgrid.com
timestamp: 1337966815
event: open
categories: newuser, transactional
email: jane.doe#sendgrid.com
timestamp: 1337966815
event: open
categories: olduser
Fiddle: https://dotnetfiddle.net/lERrmu
EDIT
If you need to go the other way, i.e. serialize, while keeping the same format, you can implement the WriteJson() method of the converter as shown below. (Be sure to remove the CanWrite override or change it to return true, or else WriteJson() will never be called.)
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
List<T> list = (List<T>)value;
if (list.Count == 1)
{
value = list[0];
}
serializer.Serialize(writer, value);
}
Fiddle: https://dotnetfiddle.net/XG3eRy

I was working on this for ages, and thanks to Brian for his answer.
All I am adding is the vb.net answer!:
Public Class SingleValueArrayConverter(Of T)
sometimes-array-and-sometimes-object
Inherits JsonConverter
Public Overrides Sub WriteJson(writer As JsonWriter, value As Object, serializer As JsonSerializer)
Throw New NotImplementedException()
End Sub
Public Overrides Function ReadJson(reader As JsonReader, objectType As Type, existingValue As Object, serializer As JsonSerializer) As Object
Dim retVal As Object = New [Object]()
If reader.TokenType = JsonToken.StartObject Then
Dim instance As T = DirectCast(serializer.Deserialize(reader, GetType(T)), T)
retVal = New List(Of T)() From { _
instance _
}
ElseIf reader.TokenType = JsonToken.StartArray Then
retVal = serializer.Deserialize(reader, objectType)
End If
Return retVal
End Function
Public Overrides Function CanConvert(objectType As Type) As Boolean
Return False
End Function
End Class
then in your class:
<JsonProperty(PropertyName:="JsonName)> _
<JsonConverter(GetType(SingleValueArrayConverter(Of YourObject)))> _
Public Property YourLocalName As List(Of YourObject)
Hope this saves you some time

As a minor variation to the great answer by Brian Rogers, here are two tweaked versions of SingleOrArrayConverter<T>.
Firstly, here is a version that works for all List<T> for every type T that is not itself a collection:
public class SingleOrArrayListConverter : JsonConverter
{
// Adapted from this answer https://stackoverflow.com/a/18997172
// to https://stackoverflow.com/questions/18994685/how-to-handle-both-a-single-item-and-an-array-for-the-same-property-using-json-n
// by Brian Rogers https://stackoverflow.com/users/10263/brian-rogers
readonly bool canWrite;
readonly IContractResolver resolver;
public SingleOrArrayListConverter() : this(false) { }
public SingleOrArrayListConverter(bool canWrite) : this(canWrite, null) { }
public SingleOrArrayListConverter(bool canWrite, IContractResolver resolver)
{
this.canWrite = canWrite;
// Use the global default resolver if none is passed in.
this.resolver = resolver ?? new JsonSerializer().ContractResolver;
}
static bool CanConvert(Type objectType, IContractResolver resolver)
{
Type itemType;
JsonArrayContract contract;
return CanConvert(objectType, resolver, out itemType, out contract);
}
static bool CanConvert(Type objectType, IContractResolver resolver, out Type itemType, out JsonArrayContract contract)
{
if ((itemType = objectType.GetListItemType()) == null)
{
itemType = null;
contract = null;
return false;
}
// Ensure that [JsonObject] is not applied to the type.
if ((contract = resolver.ResolveContract(objectType) as JsonArrayContract) == null)
return false;
var itemContract = resolver.ResolveContract(itemType);
// Not implemented for jagged arrays.
if (itemContract is JsonArrayContract)
return false;
return true;
}
public override bool CanConvert(Type objectType) { return CanConvert(objectType, resolver); }
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
Type itemType;
JsonArrayContract contract;
if (!CanConvert(objectType, serializer.ContractResolver, out itemType, out contract))
throw new JsonSerializationException(string.Format("Invalid type for {0}: {1}", GetType(), objectType));
if (reader.MoveToContent().TokenType == JsonToken.Null)
return null;
var list = (IList)(existingValue ?? contract.DefaultCreator());
if (reader.TokenType == JsonToken.StartArray)
serializer.Populate(reader, list);
else
// Here we take advantage of the fact that List<T> implements IList to avoid having to use reflection to call the generic Add<T> method.
list.Add(serializer.Deserialize(reader, itemType));
return list;
}
public override bool CanWrite { get { return canWrite; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var list = value as ICollection;
if (list == null)
throw new JsonSerializationException(string.Format("Invalid type for {0}: {1}", GetType(), value.GetType()));
// Here we take advantage of the fact that List<T> implements IList to avoid having to use reflection to call the generic Count method.
if (list.Count == 1)
{
foreach (var item in list)
{
serializer.Serialize(writer, item);
break;
}
}
else
{
writer.WriteStartArray();
foreach (var item in list)
serializer.Serialize(writer, item);
writer.WriteEndArray();
}
}
}
public static partial class JsonExtensions
{
public static JsonReader MoveToContent(this JsonReader reader)
{
while ((reader.TokenType == JsonToken.Comment || reader.TokenType == JsonToken.None) && reader.Read())
;
return reader;
}
internal static Type GetListItemType(this Type type)
{
// Quick reject for performance
if (type.IsPrimitive || type.IsArray || type == typeof(string))
return null;
while (type != null)
{
if (type.IsGenericType)
{
var genType = type.GetGenericTypeDefinition();
if (genType == typeof(List<>))
return type.GetGenericArguments()[0];
}
type = type.BaseType;
}
return null;
}
}
It can be used as follows:
var settings = new JsonSerializerSettings
{
// Pass true if you want single-item lists to be reserialized as single items
Converters = { new SingleOrArrayListConverter(true) },
};
var list = JsonConvert.DeserializeObject<List<Item>>(json, settings);
Notes:
The converter avoids the need to pre-load the entire JSON value into memory as a JToken hierarchy.
The converter does not apply to lists whose items are also serialized as collections, e.g. List<string []>
The Boolean canWrite argument passed to the constructor controls whether to re-serialize single-element lists as JSON values or as JSON arrays.
The converter's ReadJson() uses the existingValue if pre-allocated so as to support populating of get-only list members.
Secondly, here is a version that works with other generic collections such as ObservableCollection<T>:
public class SingleOrArrayCollectionConverter<TCollection, TItem> : JsonConverter
where TCollection : ICollection<TItem>
{
// Adapted from this answer https://stackoverflow.com/a/18997172
// to https://stackoverflow.com/questions/18994685/how-to-handle-both-a-single-item-and-an-array-for-the-same-property-using-json-n
// by Brian Rogers https://stackoverflow.com/users/10263/brian-rogers
readonly bool canWrite;
public SingleOrArrayCollectionConverter() : this(false) { }
public SingleOrArrayCollectionConverter(bool canWrite) { this.canWrite = canWrite; }
public override bool CanConvert(Type objectType)
{
return typeof(TCollection).IsAssignableFrom(objectType);
}
static void ValidateItemContract(IContractResolver resolver)
{
var itemContract = resolver.ResolveContract(typeof(TItem));
if (itemContract is JsonArrayContract)
throw new JsonSerializationException(string.Format("Item contract type {0} not supported.", itemContract));
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
ValidateItemContract(serializer.ContractResolver);
if (reader.MoveToContent().TokenType == JsonToken.Null)
return null;
var list = (ICollection<TItem>)(existingValue ?? serializer.ContractResolver.ResolveContract(objectType).DefaultCreator());
if (reader.TokenType == JsonToken.StartArray)
serializer.Populate(reader, list);
else
list.Add(serializer.Deserialize<TItem>(reader));
return list;
}
public override bool CanWrite { get { return canWrite; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
ValidateItemContract(serializer.ContractResolver);
var list = value as ICollection<TItem>;
if (list == null)
throw new JsonSerializationException(string.Format("Invalid type for {0}: {1}", GetType(), value.GetType()));
if (list.Count == 1)
{
foreach (var item in list)
{
serializer.Serialize(writer, item);
break;
}
}
else
{
writer.WriteStartArray();
foreach (var item in list)
serializer.Serialize(writer, item);
writer.WriteEndArray();
}
}
}
Then, if your model is using, say, an ObservableCollection<T> for some T, you could apply it as follows:
class Item
{
public string Email { get; set; }
public int Timestamp { get; set; }
public string Event { get; set; }
[JsonConverter(typeof(SingleOrArrayCollectionConverter<ObservableCollection<string>, string>))]
public ObservableCollection<string> Category { get; set; }
}
Notes:
In addition to the notes and restrictions for SingleOrArrayListConverter, the TCollection type must be read/write and have a parameterless constructor.
Demo fiddle with basic unit tests here.

To handle this you have to use a custom JsonConverter. But you probably already had that in mind.
You are just looking for a converter that you can use immediately. And this offers more than just a solution for the situation described.
I give an example with the question asked.
How to use my converter:
Place a JsonConverter Attribute above the property. JsonConverter(typeof(SafeCollectionConverter))
public class SendGridEvent
{
[JsonProperty("email")]
public string Email { get; set; }
[JsonProperty("timestamp")]
public long Timestamp { get; set; }
[JsonProperty("category"), JsonConverter(typeof(SafeCollectionConverter))]
public string[] Category { get; set; }
[JsonProperty("event")]
public string Event { get; set; }
}
And this is my converter:
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System;
namespace stackoverflow.question18994685
{
public class SafeCollectionConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return true;
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
//This not works for Populate (on existingValue)
return serializer.Deserialize<JToken>(reader).ToObjectCollectionSafe(objectType, serializer);
}
public override bool CanWrite => false;
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
}
And this converter uses the following class:
using System;
namespace Newtonsoft.Json.Linq
{
public static class SafeJsonConvertExtensions
{
public static object ToObjectCollectionSafe(this JToken jToken, Type objectType)
{
return ToObjectCollectionSafe(jToken, objectType, JsonSerializer.CreateDefault());
}
public static object ToObjectCollectionSafe(this JToken jToken, Type objectType, JsonSerializer jsonSerializer)
{
var expectArray = typeof(System.Collections.IEnumerable).IsAssignableFrom(objectType);
if (jToken is JArray jArray)
{
if (!expectArray)
{
//to object via singel
if (jArray.Count == 0)
return JValue.CreateNull().ToObject(objectType, jsonSerializer);
if (jArray.Count == 1)
return jArray.First.ToObject(objectType, jsonSerializer);
}
}
else if (expectArray)
{
//to object via JArray
return new JArray(jToken).ToObject(objectType, jsonSerializer);
}
return jToken.ToObject(objectType, jsonSerializer);
}
public static T ToObjectCollectionSafe<T>(this JToken jToken)
{
return (T)ToObjectCollectionSafe(jToken, typeof(T));
}
public static T ToObjectCollectionSafe<T>(this JToken jToken, JsonSerializer jsonSerializer)
{
return (T)ToObjectCollectionSafe(jToken, typeof(T), jsonSerializer);
}
}
}
What does it do exactly?
If you place the converter attribute the converter will be used for this property. You can use it on a normal object if you expect a json array with 1 or no result. Or you use it on an IEnumerable where you expect a json object or json array. (Know that an array -object[]- is an IEnumerable)
A disadvantage is that this converter can only be placed above a property because he thinks he can convert everything. And be warned. A string is also an IEnumerable.
And it offers more than an answer to the question:
If you search for something by id you know that you will get an array back with one or no result.
The ToObjectCollectionSafe<TResult>() method can handle that for you.
This is usable for Single Result vs Array using JSON.net
and handle both a single item and an array for the same property
and can convert an array to a single object.
I made this for REST requests on a server with a filter that returned one result in an array but wanted to get the result back as a single object in my code. And also for a OData result response with expanded result with one item in an array.
Have fun with it.

Just wanted to add to #dbc excellent response above on the SingleOrArrayCollectionConverter. I was able to modify it to use with a stream from an HTTP client. Here is a snippet (you will have to set up the requestUrl (string) and the httpClient (using System.Net.Http;).
public async Task<IList<T>> HttpRequest<T>(HttpClient httpClient, string requestedUrl, CancellationToken cancellationToken)
{
using (var request = new HttpRequestMessage(HttpMethod.Get, requestedUrl))
using (var httpResponseMessage = await httpClient.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, cancellationToken))
{
if (httpResponseMessage.IsSuccessStatusCode)
{
using var stream = await httpResponseMessage.Content.ReadAsStreamAsync();
using var streamReader = new StreamReader(stream);
using var jsonTextReader = new JsonTextReader(streamReader );
var settings = new JsonSerializerSettings
{
// Pass true if you want single-item lists to be reserialized as single items
Converters = { new SingleOrArrayCollectionConverter(true) },
};
var jsonSerializer = JsonSerializer.Create(settings);
return jsonSerializer.Deserialize<List<T>>(jsonTextReader);
}
I apologize if there are missing brackets or misspellings, it was not easy to paste code in here.

I had a very similar Problem.
My Json Request was completly unknown for me.
I only knew.
There will be an objectId in it and some anonym key value pairs AND arrays.
I used it for an EAV Model i did:
My JSON Request:
{objectId": 2,
"firstName": "Hans",
"email" :[ "a#b.de","a#c.de"],
"name": "Andre",
"something" :["232","123"]
}
My Class i defined:
[JsonConverter(typeof(AnonyObjectConverter))]
public class AnonymObject
{
public AnonymObject()
{
fields = new Dictionary<string, string>();
list = new List<string>();
}
public string objectid { get; set; }
public Dictionary<string, string> fields { get; set; }
public List<string> list { get; set; }
}
and now that i want to deserialize unknown attributes with its value and arrays in it my Converter looks like that:
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
AnonymObject anonym = existingValue as AnonymObject ?? new AnonymObject();
bool isList = false;
StringBuilder listValues = new StringBuilder();
while (reader.Read())
{
if (reader.TokenType == JsonToken.EndObject) continue;
if (isList)
{
while (reader.TokenType != JsonToken.EndArray)
{
listValues.Append(reader.Value.ToString() + ", ");
reader.Read();
}
anonym.list.Add(listValues.ToString());
isList = false;
continue;
}
var value = reader.Value.ToString();
switch (value.ToLower())
{
case "objectid":
anonym.objectid = reader.ReadAsString();
break;
default:
string val;
reader.Read();
if(reader.TokenType == JsonToken.StartArray)
{
isList = true;
val = "ValueDummyForEAV";
}
else
{
val = reader.Value.ToString();
}
try
{
anonym.fields.Add(value, val);
}
catch(ArgumentException e)
{
throw new ArgumentException("Multiple Attribute found");
}
break;
}
}
return anonym;
}
So now everytime i get an AnonymObject i can iterate through the Dictionary and everytime there is my Flag "ValueDummyForEAV" i switch to the list, read the first line and split the values. After that i delete the first entry from the list and go on with iteration from the Dictionary.
Maybe someone has the same problem and can use this :)
Regards
Andre

You can use a JSONConverterAttribute as found here: http://james.newtonking.com/projects/json/help/
Presuming you have a class that looks like
public class RootObject
{
public string email { get; set; }
public int timestamp { get; set; }
public string smtpid { get; set; }
public string #event { get; set; }
public string category[] { get; set; }
}
You'd decorate the category property as seen here:
[JsonConverter(typeof(SendGridCategoryConverter))]
public string category { get; set; }
public class SendGridCategoryConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return true; // add your own logic
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
// do work here to handle returning the array regardless of the number of objects in
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
// Left as an exercise to the reader :)
throw new NotImplementedException();
}
}

You don't need any custom converters, in this case I am usually creating a very simple JsonConstructor
public partial class Item
{
// ... all class properties
[JsonConstructor]
public Item(JToken category)
{
if (category.GetType().Name == "JArray")
Category = category.ToObject<List<string>>();
else
Category = new List<string> { category.ToString() };
}
public Item() { }
}
after this you can deserialize your json using common code
List<Item> items = JsonConvert.DeserializeObject<List<Item>>(json);

I found another solution that can handle the category as string or array by using object. This way I don´t need to mess up with the json serializer.
Please give it a look if you have the time and tell me what you think. https://github.com/MarcelloCarreira/sendgrid-csharp-eventwebhook
It´s based on the solution at https://sendgrid.com/blog/tracking-email-using-azure-sendgrid-event-webhook-part-1/ but I also added date conversion from timestamp, upgraded the variables to reflect current SendGrid model (and made categories work).
I also created a handler with basic auth as option. See the ashx files and the examples.
Thank you!