使用流畅API的一对多实体框架

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; }
}

一位父母可以生很多孩子。 一个孩子可以有一个父母。 （是的，我知道，无法提出更好的例子。）

您如何使用流畅的API编写此代码？

请注意， Parent没有List<Child> Children 。 这是有意的，也是问题的一部分。

Answer 1

这是具有所需配置的完整控制台应用程序：

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());
    }
}

并将connection string添加到您的app.config ：（替换数据库等）

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

---

• 有导航属性，没有EntityTypeConfiguration

只需运行代码：

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();
    }
}

---

• 没有导航属性

您可以添加迁移：

enable-migrations

使用以下代码：

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());
    }
}

如果添加迁移：

Add-Migration FirstMigration

您将获得以下代码：

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");
    }
}

只需手动添加up方法：

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

您会得到：

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");
    }
}

现在，当您运行update-database ，您将获得所需的内容：

Answer 2

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

Answer 3

这里：

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
}

然后在您的映射上执行以下操作：

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");
        }
    }

该映射是在nhibernate中完成的，但它与实体的映射相同。

编辑：此外，如果要访问一个父级的所有子级，则应将List添加到父级实体，并在父级映射上使用HasMany对其进行映射