在playframework ebean的自定义桥梁桌 [英] Custom bridge table in playframework ebean

问题描述

我没有成功尝试创建桥表，将解决两个@ManyToMany关系。但是此表必须包含其他字段。例如：

I am unsuccessfuly trying to create bridge table that would resolve two @ManyToMany relations. However this table have to contain additional field. For example:

Course: -course_id - pk

Student: -student_id -pk

Bridge: -(course_id, student_id) - pk
        -additional_field

我的学生类看起来像这样：

My student class looks like this:

@Entity
public class Student extends Model {

    @Id
    @OneToMany
    public List<Bridge> student_id;
}

课程类别基本一样。

桥接表格如下：

@Entity
public class Bridge extends Model{

    @EmbeddedId 
    public compound_key student_course;

    public String additional_field;

    @Embeddable
    public class compound_key{

        @ManyToOne
        public Student student_id;

        @ManyToOne
        public Student course_id;

    }

}

帮助。

推荐答案

我找到了以下解决方案。这是一个在Bridge中没有复合键的解决方案。我在Bridge类中添加了正常的@Id字段，并且关系与Student和Course是正常关系。
此解决方案在数据库的bridge表中包含一个附加的id字段。

I have found the following solution. This is a solution without a composite key in Bridge. I added normal @Id field in Bridge class and relations to Student and Course are normal relations. This solution contains an additional 'id' field in the 'bridge' table in the database.

这是代码：

Student.java：

Student.java:

@Entity
public class Student extends Model {

    @Id
    public Integer id;

    @OneToMany(mappedBy="student")
    public List<Bridge> bridges;

    public static Finder<Integer,Student> find = new Finder<Integer,Student>(
        Integer.class, Student.class
    ); 
}

Course.java：

Course.java:

@Entity
public class Course extends Model {

    @Id
    public Integer id;

    @OneToMany(mappedBy="course")
    public List<Bridge> bridges;

    public static Finder<Integer,Course> find = new Finder<Integer,Course>(
        Integer.class, Course.class
    ); 
}

Bridge.java：

Bridge.java:

@Entity
public class Bridge extends Model {

    @Id
    public Integer id;

    @ManyToOne public Student student;

    @ManyToOne public Course course;

    public String additional_field;

    public static Finder<Integer,Bridge> find = new Finder<Integer,Bridge>(
        Integer.class, Bridge.class
    ); 
}

EDIT

经过多次尝试，我在Bridge类中找到了带有复合键的解决方案。课程学生和课程与以前的解决方案相同。

After many attempts I have found solution with composite key in Bridge class. Classes Student and Course are the same as in previous solution.

Bridge.java更改为以下内容：

Bridge.java changed to following:

@Entity
public class Bridge extends Model {

    Bridge() {
        bridgeId = new BridgeId();      
    }

    @EmbeddedId
    protected BridgeId bridgeId;

    @ManyToOne
    @JoinColumn(name = "student_id", insertable = false, updatable = false)
    private Student student;

    @ManyToOne 
    @JoinColumn(name="course_id", insertable = false, updatable = false)
    private Course course;

    public String additional_field;

    public Student getStudent() {
        return student;
    }

    public void setStudent(Student aStudent) {
        student=aStudent;
        bridgeId.student_id = aStudent.id;
    }

    public Course getCourse() {
        return course;
    }

    public void setCourse(Course aCourse){
        course=aCourse;
        bridgeId.course_id = aCourse.id;
    }
}

还有额外的BridgeId.java:

And there is additional BridgeId.java:

@Embeddable
public class BridgeId implements Serializable
{
    public Integer student_id;

    public Integer course_id;

    public int hashCode() {
        return student_id + course_id;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) 
            return true;
        BridgeId b = (BridgeId)obj;
        if(b==null)
            return false;
        if (b.student_id == student_id && b.course_id == course_id) {
            return true;
        }
        return false;
    }
}

在此代码中更重要的是： p>

What is more important in this code is:

1. 嵌入式ID的字段映射到与ManyToOne关系相同的列。


2. student_id和course_id值的值从嵌入式ID而不是关系中插入。这是因为关系的属性可插入和可更新设置为false。


3. 我必须为student和course字段添加getter和setters。在设置我更新嵌入键的字段。

上面的解决方案有几个解决方法。但我不能找到更容易和更清洁的一个。

Above solution has several workarounds. But I wasn't ableto find easier and cleaner one.

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