Entity Framework Relationship 汇总

关键词汇解释

required / optional	必须 / 可空
principal / dependent	表示哪个是主键表 / 表示哪个是外键表
hasrequired / withrequired	has表示的是正向的关系，则with表示的是反向关系

数据加载

如果用virtual关键字，则标识为该属性会懒加载(第一次用的时候加载)
如果不用virtual关键字，则需要用include主动标识立即加载
可以关闭懒加载：this.Configuration.LazyLoadingEnabled = false;

一对一或一对零关系

public class user
{
    public int id { get; set; }
    public string code { get; set; }
    public string name { get; set; }
}
public class dep
{
    public int id { get; set; }
    public virtual user user { get; set; }
}
public class MyContext : DbContext
{
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<dep>()
            .HasRequired(d => d.user)
            .WithOptional();
    }
}

说明：dep里user不能为空，user里不包含dep的导航

如果改为：

modelBuilder.Entity<dep>()
                .HasRequired(d => d.user)
                .WithRequiredDependent();

则：两边都不能为空

多对多关系

public class user
{
   public int id { get; set; }
   public string code { get; set; }
   public string name { get; set; }
   public virtual ICollection<dep> Deps { get; set; }
}
public class dep
{
   public int id { get; set; }
   public virtual ICollection<user> Users { get; set; }
}
public class MyContext : DbContext
{
   protected override void OnModelCreating(DbModelBuilder modelBuilder)
   {
       modelBuilder.Entity<dep>()
           .HasMany(d => d.Users)
           .WithMany(user => user.Deps);
   }
}

这个简单，不解释

一对多关系

public class user
{
   public int id { get; set; }
   public string code { get; set; }
   public string name { get; set; }
   public int DepId { get; set; }
   public virtual dep Dep { get; set; }
}
public class dep
{
   public int id { get; set; }
   public virtual ICollection<user> Users { get; set; }
}
public class MyContext : DbContext
{
   protected override void OnModelCreating(DbModelBuilder modelBuilder)
   {
       modelBuilder.Entity<user>()
           .HasRequired(u => u.Dep)
           .WithMany(d => d.Users)
           .HasForeignKey(u => u.DepId)
           .WillCascadeOnDelete(false);
   }
}

说明：dep里包含多个user,user里包含一个dep,显示指定外键列为DepId(如果不指定，自动生成的数据库里外键列为Dep_id);

WillCascadeOnDelete(false)表示不级联删除

组合外键

public class user
{
  public int id { get; set; }
  public string code { get; set; }
  public string name { get; set; }
  public int DepId { get; set; }
  public string DepCode { get; set; }
  public virtual dep Dep { get; set; }
}
public class dep
{
  public int id { get; set; }
  public string code { get; set; }
  public virtual ICollection<user> Users { get; set; }
}
public class MyContext : DbContext
{
  protected override void OnModelCreating(DbModelBuilder modelBuilder)
  {
      modelBuilder.Entity<dep>().HasKey(d => new { d.id, d.code });

      modelBuilder.Entity<user>()
          .HasRequired(c => c.Dep)
          .WithMany(d => d.Users)
          .HasForeignKey(d => new { d.DepId, d.DepCode });

  }
}

简单不解释

重命名外键列

modelBuilder.Entity<user>()
                .HasRequired(c => c.Dep)
                .WithMany(t => t.Users)
                .Map(m => m.MapKey("NewUserID"));