Mapping composite keys using EF code first

Question

Sql server table   SomeId PK varchar 50  not null  OtherId PK int not null   How should I map this in EF 6 code first   public class MyTable        Key      public string SomeId   get  set          Key      public int OtherId   get  set        I ve seen some examples where you have to set the order for each column  is that required   Is there official documentation on this somewhere

User · Answer

I thought I would add to this question as it is the top google search result.

As has been noted in the comments, in EF Core there is no support for using annotations (Key attribute) and it must be done with fluent.

As I was working on a large migration from EF6 to EF Core this was unsavoury and so I tried to hack it by using Reflection to look for the Key attribute and then apply it during OnModelCreating

// get all composite keys (entity decorated by more than 1 [Key] attribute
foreach (var entity in modelBuilder.Model.GetEntityTypes()
    .Where(t => 
        t.ClrType.GetProperties()
            .Count(p => p.CustomAttributes.Any(a => a.AttributeType == typeof(KeyAttribute))) > 1))
{
    // get the keys in the appropriate order
    var orderedKeys = entity.ClrType
        .GetProperties()
        .Where(p => p.CustomAttributes.Any(a => a.AttributeType == typeof(KeyAttribute)))
        .OrderBy(p => 
            p.CustomAttributes.Single(x => x.AttributeType == typeof(ColumnAttribute))?
                .NamedArguments?.Single(y => y.MemberName == nameof(ColumnAttribute.Order))
                .TypedValue.Value ?? 0)
        .Select(x => x.Name)
        .ToArray();

    // apply the keys to the model builder
    modelBuilder.Entity(entity.ClrType).HasKey(orderedKeys);
}

I haven't fully tested this in all situations, but it works in my basic tests. Hope this helps someone

User · Answer

You definitely need to put in the column order  otherwise how is SQL Server supposed to know which one goes first  Here s what you would need to do in your code   public class MyTable      Key  Column Order   0     public string SomeId   get  set        Key  Column Order   1     public int OtherId   get  set        You can also look at this SO question  If you want official documentation  I would recommend looking at the official EF website  Hope this helps   EDIT  I just found a blog post from Julie Lerman with links to all kinds of EF 6 goodness  You can find whatever you need here

User · Answer

For Mapping Composite primary key using Entity framework we can use two approaches   1  By Overriding the OnModelCreating   Method   For ex  I have the model class named VehicleFeature as shown below   public class VehicleFeature       public int VehicleId   get  set        public int FeatureId get set       public Vehicle Vehicle get set       public Feature Feature get set       The Code in my DBContext would be like    public class VegaDbContext   DbContext       public DbSet lt Make gt  Makes get set        public DbSet lt Feature gt  Features get set       public VegaDbContext DbContextOptions lt VegaDbContext gt  options  base options                                         we override the OnModelCreating method here      protected override void OnModelCreating ModelBuilder modelBuilder                modelBuilder Entity lt VehicleFeature gt    HasKey vf  gt  new  vf VehicleId  vf FeatureId              2  By Data Annotations   public class VehicleFeature        DatabaseGenerated DatabaseGeneratedOption Identity          Key      public int VehicleId   get  set         DatabaseGenerated DatabaseGeneratedOption Identity           Key      public int FeatureId get set       public Vehicle Vehicle get set       public Feature Feature get set       Please refer the below links for the more information   1  https   msdn microsoft com en-us library jj591617 v vs 113  aspx  2  How to add a composite unique key using EF 6 Fluent Api

User · Answer

Through Configuration  you can do this   Model1       int fk one      int fk two    Model2       int pk one      int pk two      then in the context config  public class MyContext   DbContext       protected override void OnModelCreating DbModelBuilder modelBuilder                modelBuilder Entity lt Model1 gt                 HasRequired e   gt  e Model2               WithMany e   gt  e Model1s               HasForeignKey e   gt  new   e fk one  e fk two                 WillCascadeOnDelete false

[c#] Mapping composite keys using EF code first

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