How do you read a simple value out of some json using System.Text.Json?

问题

I have this json

{"id":"48e86841-f62c-42c9-ae20-b54ba8c35d6d"}

How do I get the 48e86841-f62c-42c9-ae20-b54ba8c35d6d out of it? All examples I can find show to do something like

var o = System.Text.Json.JsonSerializer.Deserialize<some-type>(json);
o.id // <- here's the ID!

But I don't have a type that fits this definition and I don't want to create one. I've tried deserializing to dynamic but I was unable to get that working.

var result = System.Text.Json.JsonSerializer.Deserialize<dynamic>(json);
result.id // <-- An exception of type 'Microsoft.CSharp.RuntimeBinder.RuntimeBinderException' occurred in System.Linq.Expressions.dll but was not handled in user code: ''System.Text.Json.JsonElement' does not contain a definition for 'id''

Can anyone give any suggestions?

edit:

I just figured out I can do this:

Guid id = System.Text.Json.JsonDocument.Parse(json).RootElement.GetProperty("id").GetGuid();

This does work - but is there a better way?

回答1:

you can deserialize to a Dictionary:

var dict = System.Text.Json.JsonSerializer.Deserialize<Dictionary<string, string>>(json)

Or just deserialize to Object which will yield a JsonElement that you can call GetProperty on.

回答2:

I've recently migrated a project from ASP.NET Core 2.2 to 3, and I'm having this inconvenience. In our team we value lean dependencies, so we are trying to avoid including Newtonsoft.JSON back and try using System.Text.Json. We also decided not to use a ton of POCO objects just for JSON serialization, because our backend models are more complex than needed for Web APIs. Also, because of nontrivial behaviour encapsulation, the backend models cannot be easily used to serialize/deserialize JSON strings.

I understand that System.Text.Json is supposed to be faster than Newtonsoft.JSON, but I believe this has a lot to do with ser/deser from/to specific POCO classes. Anyway, speed was not on our list of pros/cons for this decision, so YMMV.

Long story short, for the time being I wrote a small dynamic object wrapper that unpacks the JsonElements from System.Text.Json and tries to convert/cast as best as possible. The typical usage is to read the request body as a dynamic object. Again, I'm pretty sure this approach kills any speed gains, but that was not a concern for our use case.

This is the class:

    public class ReflectionDynamicObject : DynamicObject {
        public JsonElement RealObject { get; set; }

        public override bool TryGetMember (GetMemberBinder binder, out object result) {
            // Get the property value
            var srcData = RealObject.GetProperty (binder.Name);

            result = null;

            switch (srcData.ValueKind) {
                case JsonValueKind.Null:
                    result = null;
                    break;
                case JsonValueKind.Number:
                    result = srcData.GetDouble ();
                    break;
                case JsonValueKind.False:
                    result = false;
                    break;
                case JsonValueKind.True:
                    result = true;
                    break;
                case JsonValueKind.Undefined:
                    result = null;
                    break;
                case JsonValueKind.String:
                    result = srcData.GetString ();
                    break;
                case JsonValueKind.Object:
                    result = new ReflectionDynamicObject {
                        RealObject = srcData
                    };
                    break;
                case JsonValueKind.Array:
                    result = srcData.EnumerateArray ()
                        .Select (o => new ReflectionDynamicObject { RealObject = o })
                        .ToArray ();
                    break;
            }

            // Always return true; other exceptions may have already been thrown if needed
            return true;
        }
    }

and this is an example usage, to parse the request body - one part is in a base class for all my WebAPI controllers, that exposes the body as a dynamic object:

    [ApiController]
    public class WebControllerBase : Controller {

        // Other stuff - omitted

        protected async Task<dynamic> JsonBody () {
            var result = await JsonDocument.ParseAsync (Request.Body);
            return new ReflectionDynamicObject {
                RealObject = result.RootElement
            };
        }
    }

and can be used in the actual controller like this:

//[...]
    [HttpPost ("")]
    public async Task<ActionResult> Post () {
        var body = await JsonBody ();
        var name = (string) body.Name;
        //[...]
    }
//[...]

If needed, you can integrate parsing for GUIDs or other specific data types as needed - while we all wait for some official / framework-sanctioned solution.

回答3:

update to .NET Core 3.1 to support

public static dynamic FromJson(this string json, JsonSerializerOptions options = null)
    {
        if (string.IsNullOrEmpty(json))
            return null;

        try
        {
            return JsonSerializer.Deserialize<ExpandoObject>(json, options);
        }
        catch
        {
            return null;
        }
    }

来源：https://stackoverflow.com/questions/57700678/how-do-you-read-a-simple-value-out-of-some-json-using-system-text-json

标签

.net-core

system.text.json