NHibernate初学六之关联多对多关系

1：创建三张表T_Course、T_Student、T_Middle；其中一个学生可以对应多个课程，一个课程也可以对应多个学生，用T_Middle存放它们的关系内容；

CREATE TABLE [dbo].[T_Course](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [CourseName] [varchar](50) COLLATE Chinese_PRC_CI_AS NULL,
 CONSTRAINT [PK_T_Course] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]


CREATE TABLE [dbo].[T_Student](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [Name] [varchar](50) COLLATE Chinese_PRC_CI_AS NULL,
    [StudentNum] [varchar](50) COLLATE Chinese_PRC_CI_AS NULL,
 CONSTRAINT [PK_T_Student] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]


CREATE TABLE [dbo].[T_Middle](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [StudentID] [int] NULL,
    [CourseID] [int] NULL,
 CONSTRAINT [PK_T_Middle] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]

2：实体的代码，其中两个类中都有IList，中间关系类就不用创建的：

    public class CourseModel
    {
        public virtual int Id { get; set; }
        public virtual string Coursename { get; set; }
        public virtual IList Students { get; set; }
    }

    public class StudentModel
    {
        public virtual int Id { get; set; }
        public virtual string Name { get; set; }
        public virtual string Studentnum { get; set; }
        public virtual IList Courses { get; set; }
    }

3：XML映射文件的内容

3.1 CourseModel.hbm.xml文件的内容：

<?xml version="1.0" encoding="utf-8"?>
<hibernate-mapping assembly="Wujy.ModelLibrary" namespace="Wujy.ModelLibrary.Entity" xmlns="urn:nhibernate-mapping-2.2">
  <class name="CourseModel" table="T_Course" lazy="true" >
    <id name="Id" column="ID">
      <generator class="identity" />
    </id>
    <property name="Coursename">
      <column name="CourseName" sql-type="varchar" not-null="false" />
    </property>
    <bag name="Students" table="T_Middle" lazy="true" inverse="true">
      <key column="CourseID"></key>
      <many-to-many column="StudentID" class="StudentModel"></many-to-many>
    </bag>
  </class>
</hibernate-mapping>

3.2 StudentModel.hbm.xml文件的内容：

<?xml version="1.0" encoding="utf-8"?>
<hibernate-mapping assembly="Wujy.ModelLibrary" namespace="Wujy.ModelLibrary.Entity" xmlns="urn:nhibernate-mapping-2.2">
  <class name="StudentModel" table="T_Student" lazy="true" >
    <id name="Id" column="ID">
      <generator class="identity" />
    </id>
    <property name="Name">
      <column name="Name" sql-type="varchar" not-null="false" />
    </property>
    <property name="Studentnum">
      <column name="StudentNum" sql-type="varchar" not-null="false" />
    </property>
    <bag name="Courses" table="T_Middle" lazy="true" inverse="false">
      <key column="StudentID"></key>
      <many-to-many column="CourseID" class="CourseModel"></many-to-many>
    </bag>
  </class>
</hibernate-mapping>

注意：inverse：意思是反转，它指明类之间的关系由谁来进行维护。例如：班级(Class类)与学生(Student),班级-学生就是one-to-many,学生-班级就是many-to-one。它只能在 one-to-many中many的一方进行设置(当然，在many一方，可能是在<set>也可能是在<bag>也可能是在<array>中进行设置)，而对于one方，是不进行Inverse设置的。在NHibernate 社区，inverse默认值为false。

4: 主要代码如下

        protected void Button1_Click(object sender, EventArgs e)
        {
            CourseModel coursemodel = new CourseModel();
            StudentModel studentModel = new StudentModel();
            coursemodel.Coursename = "软件工程";
            int CID = CourseBll.NewAdd(coursemodel);
            
            studentModel.Name = "踏浪帅";
            studentModel.Studentnum = "20098991";
            studentModel.Courses = new List<CourseModel>();
            studentModel.Courses.Add(coursemodel);
            StudentBll.NewAdd(studentModel);
            
        }

        protected void Button2_Click(object sender, EventArgs e)
        {
            CourseModel coursemodel = new CourseModel();
            coursemodel.Coursename = "软件工程";
            CourseBll.Add(coursemodel);
        }

        protected void Button3_Click(object sender, EventArgs e)
        {
            StudentModel model = StudentBll.findById(1);
            StudentBll.Remove(model);
        }

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