Entity Type Has No Key Defined

While working on Entity Framework we face lot of problems. This article discusses and provides the solutions of a common error: ModelValidationException, Entity Type Has No Key Defined; one or more validation errors were detected during model generation.

Generally this type of errors occurred when we try to add a Controller in the project.

ModelValidationException
System.Data.Entity.EdmEntityType: EntityType “MyClass” has no key defined. Define the key for this EntityType

Some possible reasons and solutions are given bellow:

Reason 1:
Key is missing. All Entity Framework Model needs a key.

public class Customer
{
 public string CustomerName { get; set; }
}

Solution: Include a key. That means just use the code
public int ID {get;set;}

Reason 2:
Class name is not equal to ID member name.

public class CustomerClass
{
 public int CustomerID {get;set;}
}

Solution: Change CustomerID to ID, or change CustomerClass to Customer

Reason 3:
Member does not have getter/setter – it needs to be a property. If this isn’t the Key, you may see a NotSupportedException instead:
The specified type member ‘<name>’ is not supported in LINQ to Entities.
Only initializers, entity members, and entity navigation properties are supported.

public class Customer
{
 public int CustomerID;
}

Solution: add {get;set;}
public int CustomerID {get;set;};

Reason 4:
The ID member is not public

public class Customer
{
 protected int ID {get;set;};
}

Solution: Member must be public.
public int ID {get;set;};

Reason 5:
There is confusion in Entity Framework. Multiple ID is present.

public class Customer
{
 public int anID { get; set; }
 public int anotherID { get; set; }
}

Solution: Just add [Key] to give Entity Framework a hint to clarify what is the primary key. You may include the namespace System.ComponentModel.DataAnnotations;

public class Customer
 {
 [Key]
 public int anID { get; set; }
 public int anotherID { get; set; }
 }

That’s all about the error entity type has no key defined.