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))]
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;
}
I am writing a Cmdlet and need to pass object structures into an API client that may contain PSObjects. Currently, these serialise as a JSON string containing CLIXML. Instead, I need it to be treated like an object (including the NoteProperties in PSObject.Properties as properties, and recursively serialising their values).
I tried writing my own JsonConverter but for some reason it only gets called for the top level object, not for nested PSObjects:
public class PSObjectJsonConverter : JsonConverter {
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) {
if (value is PSObject) {
JObject obj = new JObject();
foreach (var prop in ((PSObject)value).Properties) {
obj.Add(new JProperty(prop.Name, value));
}
obj.WriteTo(writer);
} else {
JToken token = JToken.FromObject(value);
token.WriteTo(writer);
}
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) {
throw new NotImplementedException();
}
public override bool CanRead {
get { return false; }
}
public override bool CanConvert(Type objectType) {
return true;
}
}
Additionally, I am using serializing to camel case using CamelCasePropertyNamesContractResolver. Is there a way to make the converter respect that?
The following converter should correctly serialize recursively nested objects of type PSObject:
public class PSObjectJsonConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return typeof(PSObject).IsAssignableFrom(objectType);
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var psObj = (PSObject)value;
writer.WriteStartObject();
foreach (var prop in psObj.Properties)
{
//Probably we shouldn't try to serialize a property that can't be read.
//https://learn.microsoft.com/en-us/dotnet/api/system.management.automation.pspropertyinfo.isgettable?view=powershellsdk-1.1.0#System_Management_Automation_PSPropertyInfo_IsGettable
if (!prop.IsGettable)
continue;
writer.WritePropertyName(prop.Name);
serializer.Serialize(writer, prop.Value);
}
writer.WriteEndObject();
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
throw new NotImplementedException();
}
public override bool CanRead { get { return false; } }
}
Notes:
In WriteJson you serialize the incoming object value as the value of each property. Surely you meant prop.Value.
By only returning true from CanConvert() when the incoming object type is of type PSObject, you avoid the need to implement default serialization for non-PSObject types in WriteJson().
When you call JToken.FromObject(value) you are not using the incoming JsonSerializer serializer. Thus, any JsonSerializerSettings (including converters) will be lost. In theory you could use JToken.FromObject(Object, JsonSerializer) instead, which would preserve settings, but if you did, you would encounter the bug described in JSON.Net throws StackOverflowException when using [JsonConvert()]. Luckily, since we now return false from CanConvert when default serialization is required, this is no longer necessary.
There is no need to construct an intermediate JObject. You can write directly to the JsonWriter, which will be somewhat more performant.
Update: Additionally, I am using serializing to camel case using CamelCasePropertyNamesContractResolver. Is there a way to make the converter respect that?
Once you introduce a custom JsonConverter for your type, you need to do everything manually, including remapping of property names. Here's a version of WriteJson() that handles this by using DefaultContractResolver.NamingStrategy:
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var psObj = (PSObject)value;
writer.WriteStartObject();
var resolver = serializer.ContractResolver as DefaultContractResolver;
var strategy = (resolver == null ? null : resolver.NamingStrategy) ?? new DefaultNamingStrategy();
foreach (var prop in psObj.Properties)
{
//Probably we shouldn't try to serialize a property that can't be read.
//https://learn.microsoft.com/en-us/dotnet/api/system.management.automation.pspropertyinfo.isgettable?view=powershellsdk-1.1.0#System_Management_Automation_PSPropertyInfo_IsGettable
if (!prop.IsGettable)
continue;
writer.WritePropertyName(strategy.GetPropertyName(prop.Name, false));
serializer.Serialize(writer, prop.Value);
}
writer.WriteEndObject();
}
Note that naming strategies were introduced in Json.NET 9.0.1 so if you are using an earlier version you will need to create your own camel case name mapper such as the one shown in this answer.
In my ASP.NET web service I need all my dates to be serialized to JSON as numbers which represent a number of milliseconds passed since 1970 please. I'm using Newtonsoft.Json serializer. What do I need to do to set it up this way?
UPDATE:
the available documentation (http://www.newtonsoft.com/json/help/html/DatesInJSON.htm) only mentions serializing a single object with custom settings, what i am looking for is the default serialization settings that would govern serialization of any object
Off the top of my head I would get the ticks of the 1970 date subtract it from the ticks of the current date then divide by 10000 since there are 10000 ticks in a milisecond. This will give you a number which should be easier to serialize. You could make this an extension method of DateTime. Ticks on MSDN:
DateTime.Ticks
Have a look at this excellent blog post on creating your own DateTime converter to deal with your requirement. Example actually shows you creating UnixDateTimeConverter.
I'm not sure if this is the easiest way, but you can create a custom converter for DateTimes, then a custom JsonMediaTypeFormatter which uses that converter.
// This class overrides conversion for DateTime values
public class MyDateConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return objectType == typeof(DateTime);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
throw new NotImplementedException();
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
// Your algorithm here
var customValue = ((DateTime)value).Ticks;
writer.WriteValue(customValue);
}
}
// This formatter will create serializers with the above converter injected
public class MyJsonFormatter : JsonMediaTypeFormatter
{
public override JsonSerializer CreateJsonSerializer()
{
var serializer = base.CreateJsonSerializer();
serializer.Converters.Add(new MyDateConverter());
return serializer;
}
}
// Inside your WebApi config code, replace the default formatter with your custom one
var defaultJsonFormatter = config.Formatters.OfType<JsonMediaTypeFormatter>().First();
config.Formatters.Remove(defaultJsonFormatter);
config.Formatters.Insert(0, new MyJsonFormatter());
here is what worked:
public class MyConverter: JsonConverter
{
public override bool CanConvert(Type type)
{
return (type == typeof(DateTime) || type == typeof(DateTime?));
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
return new NotSupportedException("An attempt to read a date using a write-only converter from DateTime -> number of milliseconds since 1970.");
}
static readonly long ticksTo1970 = new DateTime(1970, 1, 1).Ticks;
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
if (value is DateTime)
{
var date = (DateTime)value;
var unixDateSpan = new TimeSpan(date.Ticks - ticksTo1970);
var milliseconds = (long)unixDateSpan.TotalMilliseconds;
writer.WriteValue(milliseconds);
}
else
{
throw new NotSupportedException("A value of unexpected type where a DateTime value is expected.");
}
}
}
public class BaseApiController : ApiController
{
[NonAction]
protected JsonResult<T> MyJson<T>(T data)
{
var result = this.Json(data);
result.SerializerSettings.Converters.Insert(0, new MyConverter());
return result;
}
}
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.
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>());
}