多级包含示例

场景

在领域驱动设计（DDD）中，多级包含是指一个领域实体包含其他领域实体的概念。下面是一个使用“班级”、“学生”和“教师”描述多级包含的例子：

解决方案

实体模型

 /// <summary>
 ///班级
 /// </summary>
 public class Class
 {
     /// <summary>
     ///班级ID
     /// </summary>
     private int _classId;

     /// <summary>
     ///编号
     /// </summary>
     private byte _number;

     /// <summary>
     ///学生
     /// </summary>
     private List<Student> _students;

     /// <summary>
     ///班级ID
     /// </summary>
     public int ClassId
     {
         get => _classId;
         set => _classId = value;
     }


     /// <summary>
     ///编号
     /// </summary>
     public byte Number
     {
         get => _number;
         set => _number = value;
     }

     /// <summary>
     ///学生
     /// </summary>
     public List<Student> Students
     {
         get => _students;
         set => _students = value;
     }
 }

 /// <summary>
 ///学生
 /// </summary>
 public class Student
 {
     /// <summary>
     ///班级ID
     /// </summary>
     private int _classId;

     /// <summary>
     ///学生姓名
     /// </summary>
     private string _name;

     /// <summary>
     ///学生ID
     /// </summary>
     private string _studentId;

     /// <summary>
     ///学生ID
     /// </summary>
     public string StudentId
     {
         get => _studentId;
         set => _studentId = value;
     }

     /// <summary>
     ///学生姓名
     /// </summary>
     public string Name
     {
         get => _name;
         set => _name = value;
     }

     /// <summary>
     ///班级ID
     /// </summary>
     public int ClassId
     {
         get => _classId;
         set => _classId = value;
     }
 }

 /// <summary>
 ///教师
 /// </summary>
 public class Teacher
 {
     /// <summary>
     ///教授班级
     /// </summary>
     private List<Class> _classes;

     /// <summary>
     ///姓名
     /// </summary>
     private string _name;

     /// <summary>
     ///教师ID
     /// </summary>
     private int _teacherId;

     /// <summary>
     ///教师ID
     /// </summary>
     public int TeacherId
     {
         get => _teacherId;
         set => _teacherId = value;
     }

     /// <summary>
     ///姓名
     /// </summary>
     public string Name
     {
         get => _name;
         set => _name = value;
     }

     /// <summary>
     ///教授班级
     /// </summary>
     public List<Class> Classes
     {
         get => _classes;
         set => _classes = value;
     }
 }

模型配置

  /// <summary>
 ///多级包含配置
 /// </summary>
 public class MultiIncludeConfiguration : MySqlContextConfigProvider
 {
     /// <summary>由派生类实现，获取数据库连接字符串。</summary>
     protected override string ConnectionString => Configuration.MySqlConnectionString;

     /// <summary>获取一个值，该值指示是否启用存储结构映射</summary>
     protected override bool EnableStructMapping => true;

     /// <summary>使用指定的建模器创建对象数据模型。</summary>
     /// <param name="modelBuilder"></param>
     protected override void CreateModel(ModelBuilder modelBuilder)
     {
         //配置班级实体型
         var classEntity = modelBuilder.Entity<Class>();
         //配置主键
         classEntity.HasKeyAttribute(p => p.ClassId).HasKeyIsSelfIncreased(true);

         //配置教师实体型
         var teacherEntity = modelBuilder.Entity<Teacher>();
         //配置主键
         teacherEntity.HasKeyAttribute(p => p.TeacherId).HasKeyIsSelfIncreased(true);

         //配置学生实体型
         var studentEntity = modelBuilder.Entity<Student>();
         //配置主键
         studentEntity.HasKeyAttribute(p => p.StudentId).HasKeyIsSelfIncreased(false);

         //隐式关联也可以独立映射 需要配置ToTable
         //配置教师与班级间的关联型
         var classTeacherAssociation = modelBuilder.Association<Class, Teacher>();
         //配置关联端 End1为Class 在关联表中Class的主键ClassId映射为ClassId
         classTeacherAssociation.AssociationEnd(p => p.End1).HasMapping("ClassId", "ClassId");
         //配置关联端 End2为Teacher 在关联表中Teacher的主键TeacherId映射为TeacherId
         classTeacherAssociation.AssociationEnd(p => p.End2).HasMapping("TeacherId", "TeacherId");
         //多对多 独立映射表
         classTeacherAssociation.ToTable("Teaching");

         //配置教师实体型中的关联引用 左端就是关联型上自己类型的这一端 即End2 右端即为另外一端End1
         teacherEntity.AssociationReference(p => p.Classes).HasLeftEnd("End2").HasRightEnd("End1");

         //配置班级和学生的关联型
         var classAssStudent = modelBuilder.Association<Class, Student>();
         //配置关联端 End1为Class 在关联表中Class的主键ClassId映射为ClassId
         classAssStudent.AssociationEnd(p => p.End1).HasMapping("ClassId", "ClassId");
         //配置关联端 End2为Student 在关联表中Teacher的主键StudentId映射为StudentId
         classAssStudent.AssociationEnd(p => p.End2).HasMapping("StudentId", "StudentId");
         //一对多 伴随表即可
         classAssStudent.ToTable("Student");

         //配置班级实体型中的关联引用 左端就是关联型上自己类型的这一端 即End1 右端即为另外一端End2
         classEntity.AssociationReference(p => p.Students).HasLeftEnd("End1").HasRightEnd("End2");
     }
 }