OData Response is an Array instead of an Object

Question

This is my url(for demonstration purpose) "https://example.com/api/Foo?$apply=groupby((bar)). and I get the response as an array.

[
    {
        "bar": "abc"
    },
    {
        "bar": "efg"
    },
    {
        "bar": "hij"
    }
]

instead of

{
    "@odata.context": "https://example.com/api/$metadata#Foo",
    "value": [
        {
            "bar": "abc"
        },
        {
            "bar": "efg"
        },
        {
            "bar": "hij"
        }
    ]
}

What is the cause of this and how can I overcome this?

There was another question similar to this. however, that didn't solve my problem

Answer 1

Maybe the issue is that your action is using the IActionResult interface instead of the ActionResult class. This causes a problem when using the $apply parameter, which leads to the metadata being excluded from the response. You also must remove the Ok() method on the return. If you're using EF and returning a IQueryable don't use ActionResult class and just put IEnumerable/IQueryable as signature of your method.

Try changing your code from

public IActionResult Get()

to (if you're using collections)

public ActionResult<IEnumerable<YourData>> Get() => _yourCollection.ToList();

or directly (if you're using EF)

public IQueryable<YourData> Get() => _yourContext.DataSet;

For more information, you can visit this link:

https://github.com/OData/AspNetCoreOData/issues/181.

Answer 2

I ran into the same issue, everything worked except it returned an array instead of the odata object. The fix ended up being changing the base class of my controller from ControllerBase to ODataController.

[ApiController]
[Route("odata")]
public class MyController: ControllerBase 

vs

[ApiController]
[Route("odata")]
public class MyController: ODataController

I figured out the mistake thanks to Jason Pan's answer, but I wanted to call out specifically what the issue ended up being. I don't have enough reputation to just leave a comment.

Answer 3

Please check the project is webapi. Please refer my code below, it works for me.

WeatherForecastController.cs

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.OData.Query;
using Microsoft.AspNetCore.OData.Routing.Controllers;

namespace WebApplication2.Controllers
{
    [ApiController]
    [Route("odata/[Controller]")]
    public class WeatherForecastController : ODataController
    {
        private static readonly string[] Summaries = new[]
        {
        "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
    };

        private readonly ILogger<WeatherForecastController> _logger;

        public WeatherForecastController(ILogger<WeatherForecastController> logger)
        {
            _logger = logger;
        }


        [EnableQuery]
        public IEnumerable<WeatherForecast> Get()
        {
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Id = index,
                Date = DateTime.Now.AddDays(index),
                TemperatureC = Random.Shared.Next(-20, 55),
                Summary = Summaries[Random.Shared.Next(Summaries.Length)]
            })
            .ToArray();
        }
    }
}

Program.cs

using Microsoft.AspNetCore.OData;
using Microsoft.OData.Edm;
using Microsoft.OData.ModelBuilder;

namespace WebApplication2
{
    public class Program
    {
        public static void Main(string[] args)
        {
            static IEdmModel GetEdmModel()
            {
                ODataConventionModelBuilder builder = new();
                builder.EntitySet<WeatherForecast>(nameof(WeatherForecast));
                return builder.GetEdmModel();
            }

            var builder = WebApplication.CreateBuilder(args);

            // Add services to the container.

            //builder.Services.AddControllers();
            builder.Services.AddControllers().AddOData(options => options.EnableQueryFeatures().AddRouteComponents("odata", GetEdmModel()).Filter().Select().Expand());
            // Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
            builder.Services.AddEndpointsApiExplorer();
            builder.Services.AddSwaggerGen();

            var app = builder.Build();

            // Configure the HTTP request pipeline.
            if (app.Environment.IsDevelopment())
            {
                app.UseSwagger();
                app.UseSwaggerUI();
            }

            app.UseHttpsRedirection();

            app.UseAuthorization();


            app.MapControllers();

            app.Run();
        }
    }
}

WeatherForecast Model

using System.ComponentModel.DataAnnotations;

namespace WebApplication2
{
    public class WeatherForecast
    {
        [Key]
        public int Id { get; set; }
        public DateTime Date { get; set; }

        public int TemperatureC { get; set; }

        public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);

        public string? Summary { get; set; }
    }
}

Test Result