How can I get independent JSON reference resolution between requests in ASP.NET Core? - asp.net-core

Question

I am attempting to add a custom IReferenceResolver implementation to an ASP.NET Core 2.2 MVC API application to reduce data in a JSON payload. However the reference resolutions are being shared between different requests.
It appears that a single instance of the ReferenceResolver is shared between requests. I want the references to be resolved independent of other requests, as different users of my won't have this shared reference context.
This is my ConfigureServices method in Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc()
.SetCompatibilityVersion(CompatibilityVersion.Version_2_2)
.AddJsonOptions(opts =>
{
opts.SerializerSettings.ReferenceResolverProvider = () => new ThingReferenceResolver();
});
}
This is my controller implementation along with my custom IReferenceResolver
[Route("api/[controller]")]
[ApiController]
public class ValuesController : ControllerBase
{
[HttpGet("")]
public ActionResult<ThingsResponse> Get()
{
return new ThingsResponse
{
MainThing = new Thing { Id = "foo" },
Things = new List<Thing>
{
new Thing { Id = "foo" },
new Thing { Id = "bar" }
}
};
}
}
public class ThingsResponse
{
[JsonProperty(IsReference = true)]
public Thing MainThing { get; set; }
[JsonProperty(ItemIsReference = true)]
public List<Thing> Things { get; set; }
}
public class Thing
{
public string Id { get; set; }
}
public class ThingReferenceResolver : IReferenceResolver
{
private readonly IDictionary<string, Thing> _idReference = new Dictionary<string, Thing>();
public void AddReference(object context, string reference, object value)
{
_idReference[reference] = (Thing)value;
}
public string GetReference(object context, object value)
{
var thing = (Thing)value;
_idReference[thing.Id] = thing;
return thing.Id.ToString();
}
public bool IsReferenced(object context, object value)
{
var thing = (Thing)value;
return _idReference.ContainsKey(thing.Id);
}
public object ResolveReference(object context, string reference)
{
_idReference.TryGetValue(reference, out Thing thing);
return thing;
}
}
On my first request I get the following response:
{
"mainThing": {
"$id": "foo",
"id": "foo"
},
"things": [
{
"$ref": "foo"
},
{
"$id": "bar",
"id": "bar"
}
]
}
On my second request I get the following response:
{
"mainThing": {
"$ref": "foo"
},
"things": [
{
"$ref": "foo"
},
{
"$ref": "bar"
}
]
}
I want my second request to look like my first request i.e. repeatable outputs.

Answer 1

You get different results for the second request because MVC creates one serializer and caches it, which then caches references if you have reference tracking on like you do.
I think if you return a JsonResult with new serializer settings in each result then you won't have this problem:
new JsonResult(yourData, new JsonSerializerSettings { ... })

Answer 2

One option I have come up with is to bypass configuring the JSON serializer that MVC provides and create my own for the request in question.
[HttpGet("")]
public ActionResult<ThingsResponse> Get()
{
var serializerSettings = JsonSerializerSettingsProvider.CreateSerializerSettings();
serializerSettings.ReferenceResolverProvider = () => new ThingReferenceResolver();
return new JsonResult(
new ThingsResponse
{
MainThing = new Thing { Id = "foo" },
Things = new List<Thing>
{
new Thing { Id = "foo" },
new Thing { Id = "bar" }
}
},
serializerSettings
);
}
In my specific scenario this is OK, because I do not have many endpoints that this would need to be configured for.
This means the following code from the example Startup.cs is not needed to solve my problem (as I define it per request)
.AddJsonOptions(opts =>
{
opts.SerializerSettings.ReferenceResolverProvider = () => new ThingReferenceResolver();
});
I think I will settle on this option for my circumstances, but would love to know if there are better ways to implement it.