I have three tables like this
Table1 Student
DepID --pk
StudentID --pk
StudentName
StudentEmail

Table 2 LinkStudentCourses
DepID--pk
StudentID--pk
CourseID--pk

Table3 Courses
1.DepID--pk
2.CourseID--pk
3.CourseName
4.CourseLevel

My requirement is to get all the courses enrolled by student, I mean getting all the corresponding data from courses table based on studentID form student table

So my approach here is using many-to-many relation
I have three different classes and xml mappings
here is how I linked them through many-to many in Student xml file

<class name="com.syn.model.Student" table="Student" entity-name="student_courses">
<composite-id name="id" class="com.syn.model.StudentId">
<key-property name = "depID" column="DepID" />
<key-property name = "studentID" column="StudentID" />
</composite-id>
<property name="studentName" column="StudentName" />
<property name="studentEmail" column="StudentEmail" />
<set name="studentCourses" table="LinkStudentCourses" inverse="true">
<key not-null="true" update="false" >
<column name="DepID" />
<column name="StudentID" />
</key>
<many-to-many entity-name="courses">
<column name="DepID" />
<column name="CourseID" />
</many-to-many>
</set>
</class>

Here is the LinkStudentCourses xml mapping

<class name="com.syn.model.LinkStudentCourses" table="LinkStudentCourses" entity-name="link_student_courses">
<composite-id name="id" class="com.syn.model.LinkStudentCoursesId">
<key-property name = "depID" column="DepID" />
<key-property name = "studentID" column="StudentID" />
<key-property name = "courseID" column="CourseID" />
</composite-id>
</class>

Here is the Course table hbm

<class name="com.syn.model.Courses" table="Courses" entity-name="courses">
<composite-id name="id" class="com.syn.model.CoursesId">
<key-property name = "depID" column="DepID" />
<key-property name = "courseID" column="CourseID" />
</composite-id>
<property name="courseName" column="CourseName" />
<property name="courseLevel" column="CourseLevel" />
</class>

here is the error tomcat throwing when I run this
Repeated column in mapping for collection: student_courses.courses column: DepID

How can I solve this problem...