Attilah Attilah - 2 months ago 9
C# Question

Entity Framework CodeFirst many to many relationship with additional information

I have the following model :

class Contract
{
string ContractID{get;set;}
ICollection<Part> Parts{get;set;}
}

class Part
{
string PartID{get;set;}
ICollection<Contract> Contracts{get;set;}
}


the problem is that the relationship between Part and Contract also contains the following additional information :

class ContractParts
{
Contract{get;set;}
Part{get;set;}
Date{get;set;} //additional info
Price{get;set;} //additional info
}


How would I write the Entity Context for this ?

Answer

In such case you must model your entities this way:

public class Contract
{
   public virtual string ContractId { get; set; }
   public virtual ICollection<ContractPart> ContractParts { get; set; }
}

public class Part
{
   public virtual string PartId { get;set; }
   public virtual ICollection<ContractPart> ContractParts { get; set; }
}

public class ContractPart
{ 
   public virtual string  ContractId { get; set; }
   public virtual string PartId { get; set; }
   public virtual Contract Contract { get; set; }
   public virtual Part Part { get; set; }
   public virtual string Date { get; set; } //additional info
   public virtual decimal Price { get; set; } //additional info
}

In derived context you must define:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
   modelBuilder.Entity<ContractPart>()
               .HasKey(cp => new { cp.ContractId, cp.PartId });

   modelBuilder.Entity<Contract>()
               .HasMany(c => c.ContractParts)
               .WithRequired()
               .HasForeignKey(cp => cp.ContractId);

   modelBuilder.Entity<Part>()
               .HasMany(p => p.ContractParts)
               .WithRequired()
               .HasForeignKey(cp => cp.PartId);  
}