I'm using the official Mongo C# Driver, and RestSharp to call a Rest Api with Json.NET to perform my serialization/deserialization. Say I have a Person class as follows, which I'd like to POST & GET:
public class Person
{
[JsonProperty("_id"),JsonConverter(typeof(ObjectIdConverter))]
public ObjectId Id {get;set;}
public string Name {get;set;}
}
I create a new Person object:
var person = new Person{Id = ObjectId.GenerateId(),Name='Joe Bloggs'};
POST it, and on the server I see the following which is correct:
{ _id: 52498b56904ee108c99fbe88, name: 'Joe Bloggs'}
The problem, is when I perform a GET the ObjectId I get on the client is {0000000000000...}
i.e. not the {5249.....} I'd expect. The raw response is showing the correct value, but once I deserialize I loose it.
The ObjectIdConverter code is :
public class ObjectIdConverter : JsonConverter
{
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
serializer.Serialize(writer, value.ToString());
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
var objectId = (ObjectId)existingValue; // at this point existingValue is {000...}
return objectId;
}
public override bool CanConvert(Type objectType)
{
return (objectType == typeof (ObjectId));
}
}
Any help would be appreciated.
You are implementing the ReadJson method of the converter incorrectly. The existingValue parameter does not give you the deserialized value read from the JSON, it gives you the existing value of the object that you will be replacing. In most cases this will be null or empty. What you need to do is use the reader to get the value from the JSON, convert it as needed, then return the converted value.
Assuming your ObjectId class has a constructor that accepts a hex string, here is how you would implement the ReadJson method:
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
JToken token = JToken.Load(reader);
return new ObjectId(token.ToObject<string>());
}
Related
I am trying to deserialize the following JSON (which validates on https://jsonlint.com/):
{"pandoc-api-version":[1,22],"meta":{"title":{"t":"MetaBlocks","c":[{"t":"Para","c":[{"t":"Str","c":"Dynamic"},{"t":"Space"},{"t":"Str","c":"Language"},{"t":"Space"},{"t":"Str","c":"Runtime"}]},{"t":"Para","c":[]}]}},"blocks":[{"t":"Para","c":[{"t":"Strong","c":[{"t":"Str","c":"Bill"},{"t":"Space"},{"t":"Str","c":"Chiles"},{"t":"Space"},{"t":"Str","c":"and"},{"t":"Space"},{"t":"Str","c":"Alex"},{"t":"Space"},{"t":"Str","c":"Turner"}]}]},{"t":"Para","c":[{"t":"Emph","c":[{"t":"Strong","c":[{"t":"Str","c":"Reading"},{"t":"Space"},{"t":"Str","c":"this"},{"t":"Space"},{"t":"Str","c":"Document:"}]}]}]}]}
into the following classes:
internal record TagContent(string T, OneOf<TagContent[], string>? C);
internal class RawPandoc {
[JsonProperty] public int[] PandocApiVersion = default!;
[JsonProperty] public Dictionary<string, TagContent> Meta = default!;
[JsonProperty] public TagContent[] Blocks = default!;
}
using the following code:
var settings = new JsonSerializerSettings {
ContractResolver = new DefaultContractResolver { NamingStrategy = new KebabCaseNamingStrategy() },
Converters = new JsonConverter[] { new OneOfJsonConverter() }
};
var pandoc = JsonConvert.DeserializeObject<RawPandoc>(s, settings);
and I get the following error:
Unexpected token when deserializing object: StartObject. Path 'meta.title.c[0]', line 1, position 69.
How can I resolve this?
For completeness, here is the current and incomplete code for OneOfJsonConverter. OneOf is a library for union types in C#:
using OneOf;
namespace PandocFilters {
public class OneOfJsonConverter : JsonConverter {
public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer) {
if (value is IOneOf of) {
value = of.Value;
}
serializer.Serialize(writer, value);
}
public override object? ReadJson(JsonReader reader, Type objectType, object? existingValue, JsonSerializer serializer) {
if (reader.Value is null) { return null; }
// TODO not implemented yet
return reader.Value;
}
public override bool CanConvert(Type objectType) => objectType.UnderlyingIfNullable().GetInterfaces().Contains(typeof(IOneOf));
}
}
Problem is you are not advancing the reader in your ReadJson implementation. You declared your converter can handle IOneOf objects, and so JSON.NET expects your converter to actually read and handle it, however it does nothing as of now. So ReadJson is called (at the start of first array in json which should be deserialized to OneOf), and then after it returns - reader position is still where it was before (at start of array), which is not what JSON.NET expects. Then it fails trying to continue reading next object, because its assumptions are violated. So, just implement ReadJson, and meanwhile you can advance a reader for example like that:
public override object? ReadJson(JsonReader reader, Type objectType, object? existingValue, JsonSerializer serializer) {
// advance reader as expected
var eitherStringOrArray = JObject.ReadFrom(reader);
return reader.Value;
}
Using json.net this test fails by default:
JsonConvert.DeserializeObject(
JsonConvert.SerializeObject(new object()),
typeof(object)
).ShouldBeOfType<object>(); // actual type is JObject
Is there a way to change this behavior, so it deserializes to the actual requested type?
You have a degenerate test case there. If you instruct Json.Net to deserialize into type object, you are telling it that the JSON could represent any possible object. So it will choose to use a JObject in that case, since you were not specific and a JObject can handle any JSON object. It is not expecting that you want to deserialize into a literal empty object instance, because that is not a very useful thing to do. If the JSON contained any data at all, you would not be able to access that data after the deserialization: object has no properties!
You can fix your test by creating an empty class Foo and using that in place of object:
JsonConvert.DeserializeObject(
JsonConvert.SerializeObject(new Foo()), typeof(Foo)
).ShouldBeOfType<Foo>();
If you really do need to force Json.Net to deserialize into an empty object instance whenever object is specified as the type, you can do it using a custom JsonConverter like this:
public class EmptyObjectConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return objectType == typeof(object);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
JToken token = JToken.Load(reader); // consume the JSON object from the reader
return token.Type == JTokenType.Null ? null : new object();
}
public override bool CanWrite
{
get { return false; }
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
Then pass an instance of the converter to JsonConvert.DeserializeObject():
JsonConvert.DeserializeObject(
JsonConvert.SerializeObject(new object()),
typeof(object),
new EmptyObjectConverter()
).ShouldBeOfType<object>();
Fiddle: https://dotnetfiddle.net/7xZ7tm
I'm using Json.NET to serialize validation data for data field. On the .NET side, validation data is a list of ValidationAttribute objects. However, I'd like to serialize them in a special form like this:
[
{ Type: 'Required', ErrorMessage: '{FieldName} is required' },
{ Type: 'RegularExpression', Pattern: '^\d+$', ErrorMessage: '...'
]
In an ideal solution I could simply intercept the object before serialization and, I could create a corresponding Dictionary<string, object> object to serialize instead of the original one.
Are there any solutions for this scenario?
You can implement your own JsonConverter class and convert your collection as you wish.
You just need to create you class and inherit it from JsonConverter
public class YourSerializer : 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)
{
throw new NotImplementedException();
}
public override bool CanConvert(Type objectType)
{
return typeof(YourClassName).IsAssignableFrom(objectType);
}
}
and then you need to decorate your class which will be serialized with the attribute (looks like it's not what you want)
[JsonConverter(typeof(YourSerializer))]
public class YourClassName
{
public string Name { get; set; }
public string Value { get; set; }
}
or, pass an instance of your serializer to Serialize methos:
string json = JsonConvert.SerializeObject(sourceObj, Formatting.Indented, new YourSerializer(typeof(yourClassName)));
Here is a few links:
http://www.newtonsoft.com/json/help/html/CustomJsonConverter.htm
http://blog.maskalik.com/asp-net/json-net-implement-custom-serialization/
Hope, it will help.
I’m using Json.net to deserialize json data received by Web API call. Some fields often have html-encoded characters like " or & How can I have this characters automatically decoded during deserialization?
I came to 2 possible solutions:
Calling System.Web.HttpUtility.HtmlDecode() in property setter like:
public string Title
{
set
{
title = System.Web.HttpUtility.HtmlDecode(value);
}
}
Writing custom JsonConverter that calls System.Web.HttpUtility.HtmlDecode() in ReadJson() method:
public class HtmlEncodingConverter : Newtonsoft.Json.JsonConverter
{
public override bool CanConvert(Type objectType)
{
return objectType == typeof(String);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
return System.Web.HttpUtility.HtmlDecode((string)reader.Value);
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
writer.WriteRawValue(System.Web.HttpUtility.HtmlEncode((string)value));
}
}
But is there any built-in solution that allows to perform html-decoding during json deserialization without additional code?
System.Net.WebUtility.HtmlDecode()
or
HttpUtility.HtmlDecode()
is the way to go, nothing built in regarding the JsonSerializer.
How can I customize the serialized output of ASP.NET Web API?
Let's say, I want all values in uppercase.
You have access to the JSON.NET serializer settings. With JSON.NET you can overide conversions using converters e.g. this datetime one.
You can also implement your own from inheritting from the abstract JsonConverter. See here for details.
For your example create the converter:
public class UpperCaseStringConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return objectType == typeof(string);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
return reader.Value.ToString();
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var outputValue = value as string;
writer.WriteValue(outputValue == null ? null : outputValue.ToUpper());
}
}
And then to register this globally add this config:
Registration example from here
JsonMediaTypeFormatter jsonFormatter = GlobalConfiguration.Configuration.Formatters.JsonFormatter;
JsonSerializerSettings jSettings = new Newtonsoft.Json.JsonSerializerSettings();
jSettings.Converters.Add(new UpperCaseStringConverter());
jsonFormatter.SerializerSettings = jSettings;
To add to a single property on a model just add the annotation:
[JsonConverter(typeof(UpperCaseStringConverter))]