JSON Circular Reference Loop Error running Raw SQL in Web API using EF Core

I had a complex stored procedure that I needed to run using EF core in a Web API project. I cannot use LINQ to represent this query. I have followed all best practices outlined here;

Everything worked great except raw sql endpoint. It started giving me “Circular Reference loop error”. To keep thing simple, I am returning DTO from endpoint not the entity.

Newtonsoft.Json.JsonSerializationException: Self referencing loop detected for property 'task' with type 'System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[System.Collections.Generic.IEnumerable`1[FM.Service.Shared.DTO.TranMasterViewDto],FM.Service.LedgerTranViewService+<GetTransactionForProjectActionAsync>d__4]'. Path 'stateMachine.<>t__builder'
......

Here is my configuration before and after the fix;

Newtonsoft Configuration in program.cs file before the fix;
}).AddNewtonsoftJson()

Newtonsoft Configuration in program.cs file after the fix;
}).AddNewtonsoftJson(
    options => 
    options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore)

The error is gone and I am getting this results.

{
    "stateMachine": {
        "<>1__state": 0,
        "<>t__builder": {},
        "projectActionID": "82ee5154-971a-ed11-90e6-00155d717606",
        "trackChanges": false,
        "<>4__this": {}
    },
    "context": {},
    "moveNextAction": {
        "method": {
            "name": "MoveNext",

Wait…This is not what I expected. Why I am getting Tasks result where I need to see my Dto results.

It turns out that I am not returning results from my Async method but the task;

public async Task<IActionResult> GetTransactionForProjectActionAsync(Guid projectActionId)
{
   return Ok(_service.LedgerTranViewService.GetTransactionForProjectActionAsync(projectActionId, trackChanges: false));
        }

Fixing the return type has solved all of my problems;

return Ok(_service.LedgerTranViewService.GetTransactionForProjectActionAsync(projectActionId, trackChanges: false).Result);
        }

[
    {
        "id": 20221,
        "projectActionID": "82ee5154-971a-ed11-90e6-00155d717606",        
        "tranMasterDetail": [
            {
                "tranMasterId": "9358b0c5-6d30-ed11-90e8-00155d717606",
                "ledgerID": "63302216-0946-ea11-ac82-f81654967f7a",
                "tranDescription": "Rent paid",
                "tranDate": "2022-01-03T00:00:00",
                "tranFlag": 0,
                "tranAmount": 1300.00
            }
        ]
    }
]

Remove Newtonsoft ReferenceLoopHandler from program.cs file.

}).AddNewtonsoftJson()

Hope this will help someone.

Reference

https://stackoverflow.com/questions/62985907/avoid-or-control-circular-references-in-entity-framework-core

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