EntityType 'Category' has no key defined. Define the key for this EntityType [duplicate]

Answer 1

You should add attribute [Key] before property CatId:

        using System.ComponentModel.DataAnnotations;

        public partial class Category
        {
            [Key]
            public int CatId { get; set; }
            public string CatName { get; set; }
            public string CatDescription { get; set; }
            public List<Product> Product { get; set; }
        }

The problem is that EF can work only when it knows primary key of table. By default EF recognize as primary key property with name Id. If your table has another primary key, you can mark it with attribute [Key] or set Key with fluent configuration.

Answer 2

I was able to solve this by adding a setter to my key property; I only had a getter before.

public int Id { get; set; }

Answer 3

Entity classes are auto generated..

Manual changes to those files will be overwritten if the code is regenerated.

You need to create a partial class with all your metadata

    [MetadataType(typeof(Category.CategoryMetadata))]
    public partial class Category
    {
        internal sealed class CategoryMetadata
        {
            [Key]
            public int CatId { get; set; }
            [Required]
            public string CatName { get; set; }
            public string CatDescription { get; set; }
            public List<Product> Product { get; set; }
        }
    }

Read more on MSDN

Answer 4

Just place [key] attribute on above id ..

[Table("employee")]

public class Employee
{ 

    [Key]

    public int Empno { set; get; }

    public string Empname { set; get; }      
}

Answer 5

Entity Framework uses a primary key field to create the primary key column on the generated table.

It uses convention to get this column with some variations:

• If the field is called id or any casing variance;
• If the field is called ClassNameId of any casing variance;

I may be missing some more conventions, but these are the most common cases.

If you don't have any field with this conventions you need to mark your desired primary key with the attribute [Key]:

[Key]
public int CatId { get; set; }

Answer 6

In my case I fixed this problem adding the right connectionString in the web.config/app.config file.

I had forgotten adding it and the DBContext was not able to communicate with the DB.

Hope it helps