Question

When running my first asp.net mvc application I got this error
I thought that entity framework automatically would create the keys of column names that end with Id? isnt it correct?

As you can see the ApplicantPositionID would be a table with 2 columns as primary key because it would relate to Applicants and also to Position.

One or more validation errors were detected during model generation:

System.Data.Edm.EdmEntityType: : EntityType 'ApplicantImage' has no key defined. Define the key for this EntityType.
System.Data.Edm.EdmEntityType: : EntityType 'ApplicationPositionHistory' has no key defined. Define the key for this EntityType.
System.Data.Edm.EdmEntitySet: EntityType: EntitySet �ApplicantsPositions� is based on type �ApplicantPosition� that has no keys defined.
System.Data.Edm.EdmEntitySet: EntityType: EntitySet �ApplicantImages� is based on type �ApplicantImage� that has no keys defined.
System.Data.Edm.EdmEntitySet: EntityType: EntitySet �ApplicationsPositionHistory� is based on type �ApplicationPositionHistory� that has no keys defined.

The error is thrown in this line:

public ActionResult Index()
        {
            return View(db.Positions.ToList());
        }

And my model is the following one:

namespace HRRazorForms.Models
{



    public class Position
    {
        public int PositionID { get; set; }
        [StringLength(20, MinimumLength=3)]
        public string name { get; set; }
        public int yearsExperienceRequired { get; set; }
        public virtual ICollection<ApplicantPosition> applicantPosition { get; set; }
    }

    public class Applicant
    {
        public int ApplicantId { get; set; }
        [StringLength(20, MinimumLength = 3)]
        public string name { get; set; }
        public string telephone { get; set; }
        public string skypeuser { get; set; }
        public ApplicantImage photo { get; set; }
        public virtual ICollection<ApplicantPosition> applicantPosition { get; set; }

    }

    public class ApplicantPosition
    {
        public int ApplicantID { get; set; }
        public int PositionID { get; set; }
        public virtual Position Position { get; set; }
        public virtual Applicant Applicant { get; set; }
        public DateTime appliedDate { get; set; }
        public int StatusValue { get; set; }

        public Status Status
        {
            get { return (Status)StatusValue; }
            set { StatusValue = (int)value; }
        }

        //[NotMapped]
        //public int numberOfApplicantsApplied
        //{
        //    get
        //    {
        //        int query =
        //             (from ap in Position
        //              where ap.Status == (int)Status.Applied
        //              select ap
        //                  ).Count();
        //        return query;
        //    }
        //}
    }




    public class ApplicantImage
    {
        public int ApplicantId { get; private set; }
        public byte[] Image { get; set; }
    }

    public class Address
    {
        [StringLength(20, MinimumLength = 3)]
        public string Country { get; set; }
        [StringLength(20, MinimumLength = 3)]
        public string City { get; set; }
        [StringLength(20, MinimumLength = 3)]
        public string AddressLine1 { get; set; }
        public string AddressLine2 { get; set; }    
    }



    public class ApplicationPositionHistory
    {
        public ApplicantPosition applicantPosition { get; set; }
        public Status oldStatus { get; set; }
        public Status newStatus { get; set; }
        [StringLength(500, MinimumLength = 10)]
        public string comments { get; set; }
        public DateTime dateModified { get; set; }
    }

    public enum Status
    {
        Applied,
        AcceptedByHR,
        AcceptedByTechnicalDepartment,
        InterviewedByHR,
        InterviewedByTechnicalDepartment,
        InterviewedByGeneralManager,
        AcceptedByGeneralManager,
        NotAccepted
    }



}

Answer 1

EF Code First can only infer that a property is a primary key if the property is called Id or <class name>Id (or if it is annotated with the Key attribute).
So you need to extend your e.g. ApplicantImage with an ApplicantImageId or Id property etc.

Edit: An artice about the coneventions: Conventions for Code First