CODEWITHSUNDEEP
c#asp.net-coreodata
leadfollowmove
leadfollowmove

Reputation: 79

OData ASP.Net Core Get Related Entities

I've got an OData Beta + ASP.Net Core + EF project. I'm trying to work out the OData controller functions and I'm getting an error trying to return the related entities:

Models / Customer.cs

public class Customer
{
    public int Id { get; set; }
    public string Standing { get; set; }

    public List<Person> People { get; set; }
    public List<Address> Addresses { get; set; }
}

CustomersController.cs

using System.Linq;
using Microsoft.AspNetCore.Mvc;
using Bookings_Server.EF;
using Bookings_Server.OData.Models;
using Microsoft.AspNet.OData;
using Microsoft.AspNet.OData.Routing;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using Microsoft.AspNetCore.Http;

namespace Bookings_Server.OData.Controllers
{
    [Produces("application/json")]
    [ODataRoutePrefix("customers")]
    public class CustomersController : ODataController
    {
        private readonly DataContext _context;

        public CustomersController(DataContext context)
        {
            _context = context;
        }

[EnableQuery]
[ODataRoute("({key})/people")]
public IQueryable<Customer> GetPeople([FromODataUri] int key)
{
    var result = _context.Customers.Where(m => m.Id == key).Select(m => m.People).ToList();
    return (result);
}
}

I'm getting an intellisense error under the result variable (within the return) stating:

Cannot implicitly convert type 'System.Collections.Generic.List<System.Collections.Generic.List<Bookings_Server.OData.Models.Person>>' to 'System.Linq.IQueryable<Bookings_Server.OData.Models.Customer>'. An explicit conversion exists (are you missing a cast?)

I've been looking at other OData V4 examples but they all throw implicit convert errors (assuming this is the difference of working on Aps.Net Core).

Upvotes: 0

Views: 2152

Answers (2)

leadfollowmove
leadfollowmove

Reputation: 79

Okay. With some help I managed to solve this issue. I didn't realise the [OdataRoute] is case sensitive and it was picking up People in my model and was having an issue with the fact it was people in my controller.

Changed this and everything started working as @camilo proposed.

Upvotes: 0

Camilo Terevinto
Camilo Terevinto

Reputation: 32068

First of all: you need to understand the difference between an IQueryable<T>, which represents a (normally) database query, with an IEnumerable<T>, which represents an in-memory collection or data source. So:

// WRONG
public IQueryable<Customer> GetPeople([FromODataUri] int key)

// CORRECT
public IEnumerable<Customer> GetPeople([FromODataUri] int key)

You should never return to outside your application an Entity Framework query.

Second, you want to include data from related entities, not select that data. So:

// WRONG
return _context.Customers
    .Where(m => m.Id == key)
    .Select(m => m.People) // "only give me People data"
    .ToList();

// CORRECT
return _context.Customers
    .Where(m => m.Id == key)
    .Include(m => m.People) // "give me Customer WITH People data"
    .ToList();

Mix these constructs and you end up with:

[EnableQuery]
[ODataRoute("customers({key})/people")]
public IEnumerable<Customer> GetPeople([FromODataUri] int key)
{
    return _context.Customers
        .Where(m => m.Id == key)
        .Include(m => m.People)
        .ToList();
}

One more thing to note, is that you should always use the asynchronous versions of Entity Framework Core's data access methods:

[EnableQuery]
[ODataRoute("customers({key})/people")]
public async Task<IEnumerable<Customer>> GetPeople([FromODataUri] int key)
{
    return await _context.Customers
        .Where(m => m.Id == key)
        .Include(m => m.People)
        .ToListAsync();
}

As a last comment, you should prefer returning the built-in IActionResult that allows you to easily change the response without having to throw exceptions:

[EnableQuery]
[ODataRoute("customers({key})/people")]
public async Task<IActionResult> GetPeople([FromODataUri] int key)
{
    var customers = await _context.Customers
        .Where(m => m.Id == key)
        .Include(m => m.People)
        .ToListAsync();

    // this is only an example
    if (!customers.Any())
    {
        return NotFound();
    }

    return Ok(customers);
}

Upvotes: 2

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