Question

在Custom bridge table in playframework ebean中有一个例子，说明如何使用@EmbeddedId在Java中使用Ebean映射模型。但Scala语言没有这样的例子。

假设我们在Scala中有以下3级模型：

学生班：

class Student (aId: Int, fName: String, lName: String) { 

    val id:Int=aId
    val firstName:String=fName
    val lastName:String=lName   
    var enrollments:java.util.List[Enrollment]
}

课程类：

class Course (aId: Int, aName: String) { 

    val id:Int=aId
    val name:String=aName
    var enrollments:java.util.List[Enrollment]
}

报名课程：

class Enrollment (aDesc: String, aStudent: Student, aCourse: Course) { 

    val description:String=aDesc
    val enrollmentId:EnrollmentId
    val student:Student = aStudent
    val course:Course = aCourse
}

如何在PlayFramework中使用Ebean将此模型映射到数据库？

Answer 1

这可以通过以下方式完成：

学生班：

@Entity
class Student (aId: Int, fName: String, lName: String) { 

    @Id
    val id:Int=aId

    @Column(name="first_name")
    val firstName:String=fName

    @Column(name="last_name")
    val lastName:String=lName

    @OneToMany(mappedBy="student")
    var enrollments:java.util.List[Enrollment] = _
}

课程类：

@Entity
class Course (aId: Int, aName: String) { 

    @Id
    val id:Int=aId

    @Column(name="name")
    val name:String=aName

    @OneToMany(mappedBy="course")
    var enrollments:java.util.List[Enrollment] = _
}

报名课程：

@Entity
class Enrollment (aDesc: String, aStudent: Student, aCourse: Course) { 

    @Column(name="name")
    val description:String=aDesc

    @EmbeddedId
    val enrollmentId:EnrollmentId = new EnrollmentId(aStudent.id, aCourse.id)

    @ManyToOne
    @JoinColumn(name = "student_id", insertable = false, updatable = false)
    val student:Student = aStudent

    @ManyToOne 
    @JoinColumn(name="course_id", insertable = false, updatable = false)
    val course:Course = aCourse
}

EnrollmentId类：

@Embeddable
class EnrollmentId (aStudentId: Int, aCourseId: Int) { 

    val student_id:Int = aStudentId

    val course_id:Int = aCourseId

    override def hashCode(): Int = student_id + course_id

    override def equals(that: Any): Boolean = {
        that match {
            case e: EnrollmentId => this.student_id == e.student_id && this.course_id == e.course_id 
            case _ => false
        }
    }
}

此代码中最重要的是从Enrollment到Student的关系以两种方式映射：

as @ManyToone relation
作为复合键的列

但是这种关系只能通过复合键保存。 @ManyToOne关系具有@JoinColumn属性＆＃39;可插入＆＃39;和'可更新的＆＃39;设置为false，这就是为什么不以这种方式保存它。

如何使用Scala在Ebean中映射@EmbeddedId

1 个答案: