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.

Answer 1

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:

Answer 2

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

Answer 3

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