Question

我想添加一个表来定义权限对象，而不是可以应用于许多模型。为此，我创建了一个Permission类：

public class Permission
{
    [Key]
    int PermissionID {get; set;}
    string User {get; set;}
    bool Read {get; set;}
    bool Write {get; set;}
}

然后其他对象类可以有一个Permission列表：

public class ObjectModel1
{
    [Key]
    int idObject1 {get; set;}
    ... Other properties ...
    public virtual ICollection<Permission> Permission {get; set;}
}

public class ObjectModel2
{
    [Key]
    int idObject2 {get; set;}
    ... Other properties ...
    public virtual ICollection<Permission> Permission {get; set;}
}

如何在不在每个对象的Permission类中定义外键的情况下，在Permission和其他Object类之间获得多对多的关系？

Answer 1

多对多关系将在两个实体之间有一个外部参照表：

// because Permission has a collection to ObjectModel1 and ObjectModel1 has a collection
// to permission, it is treated as a many to many relationship with an implicit
// xref between the tables. The xref will contain a foreign key to each entity that is
// also a composite primary key
public class Permission
{
    [Key]
    int PermissionID {get; set;}
    string User {get; set;}
    bool Read {get; set;}
    bool Write {get; set;}

    public virtual ICollection<ObjectModel1> ObjectModel1s { get; set; }
    public virtual ICollection<ObjectModel2> ObjectModel2s { get; set; }
}

public class ObjectModel1
{
    [Key]
    int idObject1 {get; set;}
    ... Other properties ...
    public virtual ICollection<Permission> Permission {get; set;}
}

public class ObjectModel2
{
    [Key]
    int idObject2 {get; set;}
    ... Other properties ...
    public virtual ICollection<Permission> Permission {get; set;}
}

实体框架将创建一个类似于PermissionObjectModel1的表，该表具有带有两个外键的复合主键（一个用于Permission，一个用于ObjectModel1）。它将为具有类似键的ObjectModel2创建另一个表。 Permission本身不存在外键。

如果您不希望获得导航属性，那么我认为您需要使用Fluent API：

public class MyDbContext : DbContext
{
    public DbSet<Permission> Permissions { get; set; }
    public DbSet<ObjectModel1> ObjectModel1s { get; set; }
    public DbSet<ObjectModel2> ObjectModel2s { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<ObjectModel1>()
            .HasMany(many => many.Permissions)
            .WithMany() // dont want navigation property on Permission
            .Map(xref => xref.MapLeftKey("ObjectModel1Id")
                             .MapRightKey("PermissionId")
                             .ToTable("ObjectModel1PermissionXref"));

        modelBuilder.Entity<ObjectModel2>()
            .HasMany(many => many.Permissions)
            .WithMany() // dont want navigation property on Permission
            .Map(xref => xref.MapLeftKey("ObjectModel2Id")
                             .MapRightKey("PermissionId")
                             .ToTable("ObjectModel2PermissionXref"));
    }
}

类似于上面代码的东西仍然会给你多对多的关系，但导航属性不会在Permission上定义。

实体框架多对多关系的实体框架

1 个答案: