使用Fluent配置表关系

转载MS官方文档:https://msdn.microsoft.com/zh-cn/data/jj591620

Configuring Relationships with the Fluent API

在EFCodeFirst Entity类写完后, 关系代码写在DBConetx类文件中

配置一：

1对0/1对1关系----Configuring a Required-to-Optional Relationship (One-to–Zero-or-One)

　　个人理解:单向关联??强弱关联??(Required有强引用,需要的意思,Optional有弱引用,可选的意思)

　　下代码分别:  配置主键; 配置主键及外键

// Configure the primary key for the OfficeAssignment
modelBuilder.Entity<OfficeAssignment>()
    .HasKey(t => t.InstructorID); 
 
// Map one-to-zero or one relationship
modelBuilder.Entity<OfficeAssignment>()
    .HasRequired(t => t.Instructor)
    .WithOptional(t => t.OfficeAssignment);

配置二：

1对1关系----Configuring a Relationship Where Both Ends Are Required (One-to-One)

　　个人理解:双向关联,但不确定这里的 Required/Optianal 是什么意思

　　HasRequired --- WithRequiredPrincipa or WithRequiredDependent  (both ends of the relationship are required)

　　HasOptianal --- WithOptionalPrincipal or WithOptionalDependent    (both ends of the relationship are required)

// Configure the primary key for the OfficeAssignment
modelBuilder.Entity<OfficeAssignment>()
    .HasKey(t => t.InstructorID); 
 
modelBuilder.Entity<Instructor>()
    .HasRequired(t => t.OfficeAssignment)
    .WithRequiredPrincipal(t => t.Instructor);

配置三：

多对多----Configuring a Many-to-Many Relationship

　　文中说明:CourseInstructor table is created with Course_CourseID and Instructor_InstructorID columns

modelBuilder.Entity<Course>()
    .HasMany(t => t.Instructors)
    .WithMany(t => t.Courses)

　　文中说明:generates the CourseInstructor table with CourseID and InstructorID columns

modelBuilder.Entity<Course>()
    .HasMany(t => t.Instructors)
    .WithMany(t => t.Courses)
    .Map(m =>
    {
        m.ToTable("CourseInstructor");
        m.MapLeftKey("CourseID");
        m.MapRightKey("InstructorID");
    });

疑问

配置四：

配置导航属性----Configuring a Relationship with One Navigation Property

　　区别:   与配置一相比,少了WitOptional(t=>tofficeAssignment)

　　　　　 与配置二相比,WithRequiredPrincipal() 中少了t => t.Instructor

　　官方说明:if want a one-to-one relationship between Instructor and OfficeAssignment, where you have a navigation property on only the Instructor type

// Configure the primary Key for the OfficeAssignment
modelBuilder.Entity<OfficeAssignment>()
    .HasKey(t => t.InstructorID); 
 
modelBuilder.Entity<Instructor>()
    .HasRequired(t => t.OfficeAssignment)
    .WithRequiredPrincipal();

配置五：

级联删除----Cascade Delete