EntityType 'x' has no key defined. Define the key for this EntityType

Question

I have this action which receives a parameter and i want to print out all the results ``` public ActionResult MusicaGenero(string genero) { //should return more than 30 rows var results = con.artista.Where(x=>x.genero==genero); return View(results); } ``` MusicaGenero have this ``` @model IEnumerable @{ ViewBag.Title = "MusicaGenero"; Layout = "~/Views/Shared/_Layout.cshtml"; }

Musica del genero de: @ViewBag.genero

@detallesMusica.artista
@detallesMusica.nombre
@detallesMusica.publicado
@detallesMusica.costo

``` How can but it throws an exception ``` System.Data.Entity.Edm.EdmEntityType: : EntityType 'album' has no key defined. Define the key for this EntityType. System.Data.Entity.Edm.EdmEntityType: : EntityType 'genero' has no key defined. Define the key for this EntityType. System.Data.Entity.Edm.EdmEntityType: : EntityType 'artista' has no…

Accepted Answer

As you can see, you are getting System.Data.Entity errors, and these, at least in this instance, have nothing to do with the code you've posted.

The Entity Framework needs some way of know what field it should define as the primary key. You can tell it how to do that in two ways.

You can define a property with the name 'Id' or append 'Id' to a property having the same name as the entity. For example, either of these would work

```
public class Album
{
  public string Id {get; set;}
  public string Name {get; set;}
}
public class Album
{
  public string AlbumId {get; set;}
  public string Name {get; set;}
}
```

EF would understand, based on the naming convention, to make the field `Id` or `AlbumId` the primary key.

The other thing you could do is use the `System.ComponentModel.DataAnnotations` `[Key]` attribute to define the key. For example, this would make the field `Name` the primary key for the table.

```
using System.ComponentModel.DataAnnotations;
//...
public class Album
{
  [Key]
  public string Name {get; set;}
}
```

EntityType 'x' has no key defined. Define the key for this EntityType

Solution

Problem