Using JsonConvert.DeserializeObject to deserialize Json to a C# POCO class
C#JsonSerializationjson.netPocoC# Problem Overview
Here is my simple User POCO class:
/// <summary>
/// The User class represents a Coderwall User.
/// </summary>
public class User
{
/// <summary>
/// A User's username. eg: "sergiotapia, mrkibbles, matumbo"
/// </summary>
public string Username { get; set; }
/// <summary>
/// A User's name. eg: "Sergio Tapia, John Cosack, Lucy McMillan"
/// </summary>
public string Name { get; set; }
/// <summary>
/// A User's location. eh: "Bolivia, USA, France, Italy"
/// </summary>
public string Location { get; set; }
public int Endorsements { get; set; } //Todo.
public string Team { get; set; } //Todo.
/// <summary>
/// A collection of the User's linked accounts.
/// </summary>
public List<Account> Accounts { get; set; }
/// <summary>
/// A collection of the User's awarded badges.
/// </summary>
public List<Badge> Badges { get; set; }
}
And the method I'm using to deserialize a JSON response into a User object (this actual JSON call is here):
private User LoadUserFromJson(string response)
{
var outObject = JsonConvert.DeserializeObject<User>(response);
return outObject;
}
This fires an exception:
> Cannot deserialize the current JSON object (e.g. {"name":"value"})
> into type
> 'System.Collections.Generic.List`1[CoderwallDotNet.Api.Models.Account]'
> because the type requires a JSON array (e.g. [1,2,3]) to deserialize
> correctly.
>
> To fix this error either change the JSON to a JSON array
> (e.g. [1,2,3]) or change the deserialized type so that it is a normal
> .NET type (e.g. not a primitive type like integer, not a collection
> type like an array or List
Having never worked with this DeserializeObject method before, I'm kind of stuck here.
I've made sure that the property names in the POCO class are the same as the names in the JSON response.
What can I try to deserialize JSON into this POCO class?
C# Solutions
Solution 1 - C#
Here is a working example.
Keypoints are:
- Declaration of
Accounts - Use of
JsonPropertyattribute
.
using (WebClient wc = new WebClient())
{
var json = wc.DownloadString("http://coderwall.com/mdeiters.json");
var user = JsonConvert.DeserializeObject<User>(json);
}
-
public class User
{
/// <summary>
/// A User's username. eg: "sergiotapia, mrkibbles, matumbo"
/// </summary>
[JsonProperty("username")]
public string Username { get; set; }
/// <summary>
/// A User's name. eg: "Sergio Tapia, John Cosack, Lucy McMillan"
/// </summary>
[JsonProperty("name")]
public string Name { get; set; }
/// <summary>
/// A User's location. eh: "Bolivia, USA, France, Italy"
/// </summary>
[JsonProperty("location")]
public string Location { get; set; }
[JsonProperty("endorsements")]
public int Endorsements { get; set; } //Todo.
[JsonProperty("team")]
public string Team { get; set; } //Todo.
/// <summary>
/// A collection of the User's linked accounts.
/// </summary>
[JsonProperty("accounts")]
public Account Accounts { get; set; }
/// <summary>
/// A collection of the User's awarded badges.
/// </summary>
[JsonProperty("badges")]
public List<Badge> Badges { get; set; }
}
public class Account
{
public string github;
}
public class Badge
{
[JsonProperty("name")]
public string Name;
[JsonProperty("description")]
public string Description;
[JsonProperty("created")]
public string Created;
[JsonProperty("badge")]
public string BadgeUrl;
}
Solution 2 - C#
Another, and more streamlined, approach to deserializing a camel-cased JSON string to a pascal-cased POCO object is to use the CamelCasePropertyNamesContractResolver.
It's part of the Newtonsoft.Json.Serialization namespace. This approach assumes that the only difference between the JSON object and the POCO lies in the casing of the property names. If the property names are spelled differently, then you'll need to resort to using JsonProperty attributes to map property names.
using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;
. . .
private User LoadUserFromJson(string response)
{
JsonSerializerSettings serSettings = new JsonSerializerSettings();
serSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();
User outObject = JsonConvert.DeserializeObject<User>(jsonValue, serSettings);
return outObject;
}
Solution 3 - C#
You could create a JsonConverter. See here for an example thats similar to your question.
Solution 4 - C#
The accounts property is defined like this:
"accounts":{"github":"sergiotapia"}
Your POCO states this:
public List<Account> Accounts { get; set; }
Try using this Json:
"accounts":[{"github":"sergiotapia"}]
An array of items (which is going to be mapped to the list) is always enclosed in square brackets.
Edit: The Account Poco will be something like this:
class Account {
public string github { get; set; }
}
and maybe other properties.
Edit 2: To not have an array use the property as follows:
public Account Accounts { get; set; }
with something like the sample class I've posted in the first edit.
Solution 5 - C#
Along the lines of the accepted answer, if you have a JSON text sample you can plug it in to this converter, select your options and generate the C# code.
If you don't know the type at runtime, this topic looks like it would fit.
Solution 6 - C#
to fix this error either change the JSON to a JSON array (e.g. [1,2,3]) or change the
deserialized type so that it is a normal .NET type (e.g. not a primitive type like
integer, not a collection type like an array or List) that can be deserialized from a
JSON object.`
The whole message indicates that it is possible to serialize to a List object, but the input must be a JSON list. This means that your JSON must contain
"accounts" : [{<AccountObjectData}, {<AccountObjectData>}...],
Where AccountObject data is JSON representing your Account object or your Badge object
What it seems to be getting currently is
"accounts":{"github":"sergiotapia"}
Where accounts is a JSON object (denoted by curly braces), not an array of JSON objects (arrays are denoted by brackets), which is what you want. Try
"accounts" : [{"github":"sergiotapia"}]
Solution 7 - C#
That's not exactly what I had in mind. What do you do if you have a generic type to only be known at runtime?
public MyDTO toObject() {
try {
var methodInfo = MethodBase.GetCurrentMethod();
if (methodInfo.DeclaringType != null) {
var fullName = methodInfo.DeclaringType.FullName + "." + this.dtoName;
Type type = Type.GetType(fullName);
if (type != null) {
var obj = JsonConvert.DeserializeObject(payload);
//var obj = JsonConvert.DeserializeObject<type.MemberType.GetType()>(payload); // <--- type ?????
...
}
}
// Example for java.. Convert this to C#
return JSONUtil.fromJSON(payload, Class.forName(dtoName, false, getClass().getClassLoader()));
} catch (Exception ex) {
throw new ReflectInsightException(MethodBase.GetCurrentMethod().Name, ex);
}
}
Solution 8 - C#
May be late but using QuickType is the easiest way to do that:
Solution 9 - C#
For anyone having this problem i was not seeing the json value properly. https://jsonutils.com/ there you can check the classes that should be generated and return ONLY ONE of those classes once you read the json in your code.
For example i needed a booklist object so my code should only read one
res = await response.Content.ReadAsAsync<BookList>();
Where booklist looks something like
public class BookList
{
[JsonProperty("data")]
public IList<Datum> Data { get; set; }
}
And in that list have smaller book clasess that the converter named Datum (just books)
public class Datum
{
[JsonProperty("id")]
public string Id { get; set; }
[JsonProperty("isbn")]
public string Isbn { get; set; }
}
Again, if you have doubts https://jsonutils.com/