使用Fluent配置表关系

时间:2022-11-21 22:17:14

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