Question

I have the following Classes and am using EF 4.2 Code First

public class PartAttribute
{
    public Part Part { get; set; }

    public PartAttributeType PartAttributeType { get; set; }

    [Timestamp]
    public byte[] Time { get; set; }

    [Required]
    public string Value { get; set; }
}

public class Part
{
    public Guid Id { get; set; }

    [Required]
    public PartType PartType { get; set; }

    [Required]
    public string SerialNumber { get; set; }

    public string Description { get; set; }

    public ICollection<Team> SelectedTeams { get; set; }
}

public class PartAttributeType
{
    public Guid Id { get; set; }

    [Required]
    public PartType PartType { get; set; }

    [Required]
    public string Name { get; set; }

    public string Description { get; set; }
}

When I build my model it creates the three tables and the relationships between the tables as I would like/expect them. I am trying to create a composite key on the PartAttribute table between the Part, PartAttributeType, and the time and I can’t seem to figure it out. When I try to add
modelBuilder.Entity<PartAttribute>().HasKey(c => new { c.Part, c.PartAttributeType, c.Time });
I get an error saying Part is not a scalar type (which it is not).

Answer 1

You need to introduce foreign key properties which can act as primary keys at the same time:

public class PartAttribute
{
    public Guid PartId { get; set; }
    public Guid PartAttributeTypeId { get; set; }

    public Part Part { get; set; }

    public PartAttributeType PartAttributeType { get; set; }

    [Timestamp]
    public byte[] Time { get; set; }

    [Required]
    public string Value { get; set; }
}

Then your mapping:

modelBuilder.Entity<PartAttribute>()
    .HasKey(c => new { c.PartId, c.PartAttributeTypeId, c.Time });

EF should be able to recognize the new properties as the foreign keys for your two navigation properties due to the naming convention.