Web APi OData V4 Issue "The entity '' does not have a key defined

Question

When I run the following sample it is throwing the following exception...

Additional information: The entity 'TestEntity' does not have a key defined.

I have configured the key using code first entity context... modelBuilder.Entity<TestEntity>().HasKey(t => t.EntityID);

What is the issue? why is OData V4 not using the configured key?

namespace WebApplication2
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API configuration and services

            // Web API routes
            config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );

            config.MapODataServiceRoute("odata", "odata", model: GetEDMModel());

        }

        private static IEdmModel GetEDMModel()
        {
            ODataModelBuilder builder = new ODataConventionModelBuilder();
            builder.EntitySet<TestEntity>("TestEntities");             
            return builder.GetEdmModel();
        }
    }


    public class TestEntity
    {
        public int EntityID { get; set; }
        public string Name { get; set; }
    }

    public partial class TestContext1 : DbContext
    {

        public TestContext1() : base("DB")
        {
        }
        public DbSet<TestEntity> Entities { get; set; }        
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<TestEntity>().HasKey(t => t.EntityID);

        }
    }

}

Abduce

Answer 1

You defined the key for the database mapping of Entity Framework but not for the OData mapping.

Try this:

 private static IEdmModel GetEDMModel()
 {
       ODataModelBuilder builder = new ODataConventionModelBuilder();
       var entitySet = builder.EntitySet<TestEntity>("TestEntities");
       entitySet.EntityType.HasKey(entity => entity.EntityID)
       return builder.GetEdmModel();
 }

Or try adding a [Key] Attribute to your TestEntity to tell OData (and Entity Framework at the same time) what Property is the key.

Like so:

using System.ComponentModel.DataAnnotations;

public class TestEntity
{
    [Key]
    public int EntityID { get; set; }
    public string Name { get; set; }
}

Sheley

In the Code first context already I mapped/configured the key. why we have to configure one more time. Moreover, same code works with OData v3 version "Microsoft.AspNet.WebApi.OData" but this is not working with "Microsoft.AspNet.OData" – Abduce

The one you configured is for Entity Framework mapping. Possibly OData requires a different mapping. You might also be able to circumvent this by adding a [Key] attribute above the EntityID property – Sheley

modelBuilder.Entity<TestEntity>().HasKey(t => t.EntityID) is nothing but [Key] attribute. But why it is working with [Key] attribute. Moreover this is supported feature in previous version. – Abduce

Possible OData is checking the [Key] attribute once you define the entity on the ODataModelBuilder. So when the attribute is not defined you'd have to tell the OData Model otherwise what to use as the Key for the entity. OData doesn't know about Entity Framework (you could put anything else as a data provider behind OData). And i'm just assuming. I'm afraid you'd have to verify it yourself. – Sheley

@Sheley your first suggestion - adding the HasKey - worked for me. Thanks! – Robomb

Answer 2

I came here from google and ran into this error, here is an example of what my class looked like

public class TestEntity
{
    [Key]
    public int EntityID { get; }//<-- missing set
    public string Name { get; set; }
}

only after I added the set to my [key] property did it get resolved. Here is the end result

public class TestEntity
{
    [Key]
    public int EntityID { get; set; }//<--- added set
    public string Name { get; set; }
}

Frigging

Same here although my setter was set to internal as it was auto-generated by the IDE. I changed to public. – Bruxelles

Answer 3

if the class name is TestEntity and the id field is EntityID this is the problem change the class name to Entity or the field name to Id or TestEntityId this worked for me ,you can check this link for more solutions if this wasn't the case.

Burgher

This seems specific to Entity Framework, not OData. – Wace