Entity Framework one to many using fluent API

Question

public class Parent
{
    public int ParentId { get; set; }
    public string Name { get; set; }
}

public class Child
{
    public int ChildId { get; set; }
    public string Name { get; set; }
    public Parent Parent { get; set; }
    public int ParentId { get; set; }
}

One parent can have many children. One child can have one parent. (Yeah, I know, couldn't come up with a better example.)

How do you write this using the fluent API?

Note that the Parent does not have a List<Child> Children. That is intentional and part of the problem.

I found this 2 seconds ago http://stackoverflow.com/q/36520955/687549 it seem there's an overload I must have missed. — PussInBoots, Oct 27 '16 at 20:45

Rafael Marques · Answer 1 · 2016-10-28T13:51:49.590

Here is a complete console application with the configuration you need:

class Program
{
    static void Main(string[] args)
    {
        var ctx = new TesteContext();
        ctx.Database.CreateIfNotExists();

        Console.ReadKey();
    }
}

public class Parent
{
    public int ParentId { get; set; }
    public string Name { get; set; }
}

public class Child
{
    public int ChildId { get; set; }
    public string Name { get; set; }
    public int ParentId { get; set; }
    public virtual Parent Parent { get; set; }
}

public class ParentConfiguration : EntityTypeConfiguration<Parent>
{
    public ParentConfiguration()
    {
        HasKey(x => x.ParentId);
    }
}

public class ChildConfiguration : EntityTypeConfiguration<Child>
{
    public ChildConfiguration()
    {
        HasKey(x => x.ChildId);

        HasRequired(x => x.Parent)
            .WithMany()
            .HasForeignKey(x => x.ParentId)
            .WillCascadeOnDelete(false);
    }
}

public class TesteContext : DbContext
{
    public DbSet<Parent> Parents { get; set; }
    public DbSet<Child> Childs { get; set; }

    public TesteContext() : base("Teste_123")
    {

    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Configurations.Add(new ParentConfiguration());
        modelBuilder.Configurations.Add(new ChildConfiguration());
    }
}

And add the connection string to you app.config: (Replacing the database, etc)

<connectionStrings>
  <add name="Teste_123" connectionString="Data Source=.\SQLEXPRESS;Initial Catalog=Teste_123;Integrated Security=True;MultipleActiveResultSets=true;" providerName="System.Data.SqlClient" />
</connectionStrings>

With navigation property and without EntityTypeConfiguration

Just run the code:

class Program
{
    static void Main(string[] args)
    {
        var ctx = new TesteContext();
        ctx.Database.CreateIfNotExists();

        Console.ReadKey();
    }
}

public class Parent
{
    public int ParentId { get; set; }
    public string Name { get; set; }
}

public class Child
{
    public int ChildId { get; set; }
    public string Name { get; set; }
    public int ParentId { get; set; }
    public Parent Parent { get; set; }
}

public class TesteContext : DbContext
{
    public DbSet<Parent> Parents { get; set; }
    public DbSet<Child> Childs { get; set; }

    public TesteContext() : base("Teste_123")
    {
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Child>()
            .HasRequired(x => x.Parent)
            .WithMany();
    }
}

Without navigation property

You can add a migration:

enable-migrations

With the code below:

public class Parent
{
    public int ParentId { get; set; }
    public string Name { get; set; }
}

public class Child
{
    public int ChildId { get; set; }
    public string Name { get; set; }
    public int ParentId { get; set; }
}

public class ParentConfiguration : EntityTypeConfiguration<Parent>
{
    public ParentConfiguration()
    {
        HasKey(x => x.ParentId);
    }
}

public class ChildConfiguration : EntityTypeConfiguration<Child>
{
    public ChildConfiguration()
    {
        HasKey(x => x.ChildId);
    }
}

public class TesteContext : DbContext
{
    public DbSet<Parent> Parents { get; set; }
    public DbSet<Child> Childs { get; set; }

    public TesteContext() : base("Teste_123")
    {

    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Configurations.Add(new ParentConfiguration());
        modelBuilder.Configurations.Add(new ChildConfiguration());
    }
}

If you add a migration:

Add-Migration FirstMigration

You will get the code below:

public partial class FirstMigration : DbMigration
{
    public override void Up()
    {
        CreateTable(
            "dbo.Children",
            c => new
                {
                    ChildId = c.Int(nullable: false, identity: true),
                    Name = c.String(),
                    ParentId = c.Int(nullable: false),
                })
            .PrimaryKey(t => t.ChildId);

        CreateTable(
            "dbo.Parents",
            c => new
                {
                    ParentId = c.Int(nullable: false, identity: true),
                    Name = c.String(),
                })
            .PrimaryKey(t => t.ParentId);
    }

    public override void Down()
    {
        DropTable("dbo.Parents");
        DropTable("dbo.Children");
    }
}

Just add manually on the up method:

AddForeignKey("dbo.Children", "ParentId", "dbo.Parents", "ParentId", cascadeDelete: false);

And you'll get:

public partial class FirstMigration : DbMigration
{
    public override void Up()
    {
        CreateTable(
            "dbo.Children",
            c => new
                {
                    ChildId = c.Int(nullable: false, identity: true),
                    Name = c.String(),
                    ParentId = c.Int(nullable: false),
                })
            .PrimaryKey(t => t.ChildId);

        CreateTable(
            "dbo.Parents",
            c => new
                {
                    ParentId = c.Int(nullable: false, identity: true),
                    Name = c.String(),
                })
            .PrimaryKey(t => t.ParentId);

        AddForeignKey("dbo.Children", "ParentId", "dbo.Parents", "ParentId", cascadeDelete: false);
    }

    public override void Down()
    {
        DropTable("dbo.Parents");
        DropTable("dbo.Children");
    }
}

Now, when you run update-database, you'll get what you want:

I only needed the .WithMany() part but +1 for the complete example. Might help others in the future. I will create a new answer tho since I want to keep it short and simple. The EntityTypeConfiguration is nice, keeps things nice and tidy but I don't need it in my app at the moment, maybe in future versions. Also, lazy loading (virtual) should be used with caution. — PussInBoots, Oct 27 '16 at 21:18
As far as I know, you can't map a relation between objects without at least one navigation property. You can try to do manually with migrations... — Rafael Marques, Oct 28 '16 at 12:54
I changed the answer, adding an example with migrations. Hope it will help ;) — Rafael Marques, Oct 28 '16 at 13:25
These are not needed: modelBuilder.Entity() .HasKey(x => x.ParentId); modelBuilder.Entity() .HasKey(x => x.ChildId); EF will take care of the primary key automatically by convention. — PussInBoots, Oct 28 '16 at 13:33
This one's not needed either: .HasForeignKey(x => x.ParentId) EF knows this by convention. — PussInBoots, Oct 28 '16 at 13:36
Also, you don't need to add cascadeDelete manually. .WillCascadeOnDelete(false) will take care of that. I believe you ran the Add-Migration command twice. And the second time you forgot the -force flag to update the migration c# code. — PussInBoots, Oct 28 '16 at 13:40
You are right, but I usually like to make explicit what I want. I'll edit removing the unnecessary code :D — Rafael Marques, Oct 28 '16 at 13:47

score 0 · Answer 2 · answered Oct 27 '16 at 21:26

0

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Child>()
            .HasRequired(c => c.Parent)
            .WithMany();
}

answered Oct 27 '16 at 21:26

PussInBoots

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Stormhashe · Answer 3 · 2016-10-27T20:49:36.853

-2

Here:

public partial class Parent {
    public virtual int ParentId 
    public virtual string Name
}

public class Child {
    public virtual int ChildId 
    public virtual string Name
    public virtual Parent Parent
}

and on your mappings, do:

public partial class ChildMap : ClassMap<Child> {
        public ChildMap(){
            Table("[child]");
            LazyLoad();
            Id(x => x.ChildId ).GeneratedBy.Identity().Column("ChildId ");
            Map(x => x.Name).Column("Name");
            References(x => x.Parent).Column("ParentId").Not.Nullable();
        }
    }

public partial class ParentMap : ClassMap<Parent> {
        public ParentMap(){
            Table("[parent]");
            LazyLoad();
            Id(x => x.ParentId).GeneratedBy.Identity().Column("ParentId");
            Map(x => x.Name).Column("Name");
        }
    }

This mapping is done in nhibernate, but it maps just the same as entity.

Edit: Also, if you want to access all childs of one parent, you should add the List to parent entity, and map it with HasMany on the parent mapping

edited Oct 27 '16 at 20:49

answered Oct 27 '16 at 20:45

Stormhashe

704
6
16

Wow. Didn't expect an NHibernate example as an answer. Interesting. The API looks flexible but a little bit too much code for my taste compared to EF. – PussInBoots Oct 27 '16 at 20:49
You have answered an EF question with an NHibernate example, The code is quite different for EF – undefined Oct 27 '16 at 20:49
Just the sintax is different, but the logic is exact the same. – Stormhashe Oct 27 '16 at 20:50
I just had a nhibernate example lying around on one of my projects, seemed a lot of work to convert it to EF. The logic of declaring the relations on both of them are very similar, just the sintax is different – Stormhashe Oct 27 '16 at 20:51

Entity Framework one to many using fluent API

3 Answers3

With navigation property and without EntityTypeConfiguration

Without navigation property