GreenDao教程(3)：一对一，一对多，多对多

1. 前言

• 主要介绍GreenDao 一对一，一对多，多对多应用
• 这部分还是有些坑的，注意看示例代码中注释即可避开
• 本文资料来源网络公开资源，并根据个人实践见解纯手打整理，如有错误请随时指出。
• 本文主要用于个人积累及分享，文中可能引用其他技术大牛文章（仅引用链接不转载），如有侵权请告知必妥善处理。

2. 一对一

2.1. 注解

@ToOne(joinProperty = "childId")

2.2. 示例

• 这里举一个简单的例子，用户对象UserBean和用户其他信息对象OtherUserInfoBean，每个用户都对应一个用户其他信息
• 查看以下代码和注释，可以清楚的了解一对一如何使用（自动注入代码可以适当忽略）
• 以下代码主要包括实体类定义（UserBean.java、OtherUserInfoBean.java），insert一组数据，delete一组数据3个部分

2.2.1. 实体类定义

以下示例为rebuild之后的代码

• UserBean.java

@Entity
public class UserBean {
    @Id
    //必须使用包装类对象类型Long，而非基本类型long
    private Long id;
    @NotNull
    private String name;
    private int age;
    private String province;
    private boolean isMale;
    private String idCard;

    //ToOne注解使用的joinProperty = "otherUserInfoId"指的是UserBean中自定义的这个otherUserInfoId
    private Long otherUserInfoId;

    //在insert时，将otherUserInfoId同一对一关联的OtherUserInfoBean的主键id绑定
    @ToOne(joinProperty = "otherUserInfoId")
    private OtherUserInfoBean otherUserInfoBean;

    //-------------------------------自动注入代码部分---开始
    @Generated(hash = 4979683)
    private transient Long otherUserInfoBean__resolvedKey;
    /**
     * Used for active entity operations.
     */
    @Generated(hash = 83707551)
    private transient UserBeanDao myDao;
    /**
     * Used to resolve relations
     */
    @Generated(hash = 2040040024)
    private transient DaoSession daoSession;


    @Generated(hash = 359442482)
    public UserBean(Long id, @NotNull String name, int age, String province,
                    boolean isMale, String idCard, Long otherUserInfoId) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.province = province;
        this.isMale = isMale;
        this.idCard = idCard;
        this.otherUserInfoId = otherUserInfoId;
    }

    @Generated(hash = 1203313951)
    public UserBean() {
    }

    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#refresh(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 1942392019)
    public void refresh() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.refresh(this);
    }

    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#update(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 713229351)
    public void update() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.update(this);
    }

    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#delete(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 128553479)
    public void delete() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.delete(this);
    }

    /**
     * called by internal mechanisms, do not call yourself.
     */
    @Generated(hash = 1952804343)
    public void setOtherUserInfoBean(OtherUserInfoBean otherUserInfoBean) {
        synchronized (this) {
            this.otherUserInfoBean = otherUserInfoBean;
            otherUserInfoId = otherUserInfoBean == null ? null : otherUserInfoBean.getId();
            otherUserInfoBean__resolvedKey = otherUserInfoId;
        }
    }

    /**
     * To-one relationship, resolved on first access.
     */
    @Generated(hash = 1275005484)
    public OtherUserInfoBean getOtherUserInfoBean() {
        Long __key = this.otherUserInfoId;
        if (otherUserInfoBean__resolvedKey == null || !otherUserInfoBean__resolvedKey.equals(__key)) {
            final DaoSession daoSession = this.daoSession;
            if (daoSession == null) {
                throw new DaoException("Entity is detached from DAO context");
            }
            OtherUserInfoBeanDao targetDao = daoSession.getOtherUserInfoBeanDao();
            OtherUserInfoBean otherUserInfoBeanNew = targetDao.load(__key);
            synchronized (this) {
                otherUserInfoBean = otherUserInfoBeanNew;
                otherUserInfoBean__resolvedKey = __key;
            }
        }
        return otherUserInfoBean;
    }

    public Long getOtherUserInfoId() {
        return this.otherUserInfoId;
    }

    public void setOtherUserInfoId(Long otherUserInfoId) {
        this.otherUserInfoId = otherUserInfoId;
    }

    public String getIdCard() {
        return this.idCard;
    }

    public void setIdCard(String idCard) {
        this.idCard = idCard;
    }

    public boolean getIsMale() {
        return this.isMale;
    }

    public void setIsMale(boolean isMale) {
        this.isMale = isMale;
    }

    public String getProvince() {
        return this.province;
    }

    public void setProvince(String province) {
        this.province = province;
    }

    public int getAge() {
        return this.age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Long getId() {
        return this.id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    /** called by internal mechanisms, do not call yourself. */
    @Generated(hash = 1491512534)
    public void __setDaoSession(DaoSession daoSession) {
        this.daoSession = daoSession;
        myDao = daoSession != null ? daoSession.getUserBeanDao() : null;
    }
    //-------------------------------自动注入代码部分---结束

    @Override
    public String toString() {
        //toString UserBean一对一关联的otherUserInfoBean时，
        //不能直接使用变量otherUserInfoBean，需要调用自动注入生成的getOtherUserInfoBean()获取关联对象
        return "UserBean{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", province='" + province + '\'' +
                ", isMale=" + isMale +
                ", idCard='" + idCard + '\'' +
                ", otherUserInfoId=" + otherUserInfoId +
                ", otherUserInfoBean=" + (getOtherUserInfoBean() == null ? "null" : getOtherUserInfoBean().toString()) +
                '}';
    }

• OtherUserInfoBean.java

@Entity
public class OtherUserInfoBean {
    @Id
    //必须使用包装类对象类型Long，而非基本类型long
    private Long id;
    private String address;
    private String tel;
    private Date birthday;

    //-------------------------------自动注入代码部分---开始
    public Date getBirthday() {
        return this.birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getTel() {
        return this.tel;
    }

    public void setTel(String tel) {
        this.tel = tel;
    }

    public String getAddress() {
        return this.address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public Long getId() {
        return this.id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    @Generated(hash = 647485055)
    public OtherUserInfoBean(Long id, String address, String tel, Date birthday) {
        this.id = id;
        this.address = address;
        this.tel = tel;
        this.birthday = birthday;
    }

    @Generated(hash = 59605238)
    public OtherUserInfoBean() {
    }
    //-------------------------------自动注入代码部分---结束

    @Override
    public String toString() {
        return "OtherUserInfoBean{" +
                "id=" + id +
                ", address='" + address + '\'' +
                ", tel='" + tel + '\'' +
                ", birthday=" + birthday +
                '}';
    }

2.2.2. insert一组数据

以下代码，其中GreenDaoUtil是获取DaoSession的一个单例工具工具类。获取DaoSession可以通过自己的方式获取，但请保持单例。

UserBean user = new UserBean();
user.setAge((int) (Math.random() * 100 + 10));
user.setIdCard((int) (Math.random() * 10000) + "123456789");
if (Math.random() * 100 > 50) {
    user.setIsMale(true);
} else {
    user.setIsMale(false);
}
user.setName("李看啥" + (int) (Math.random() * 1000));
user.setProvince("shanhaijing");
Long otherUserInfoId = (long) (Math.random() * 1000);

//只setOtherUserInfoId，不setOtherUserInfoBean
user.setOtherUserInfoId(otherUserInfoId);

//insert user
GreenDaoUtil.getDaoSession(activity).getUserBeanDao().insert(user);


OtherUserInfoBean otherUserInfoBean = new OtherUserInfoBean();

//主键id使用user的otherUserInfoId
otherUserInfoBean.setId(otherUserInfoId);

otherUserInfoBean.setTel(String.valueOf((i + 100) * 19 + Math.random() * 100));
otherUserInfoBean.setAddress("dongshanjing");
Date date = new Date();
date.setTime((long) (System.currentTimeMillis() - Math.random() * 2000000000));
otherUserInfoBean.setBirthday(date);

//insert otherUserInfoBean
GreenDaoUtil.getDaoSession(activity).getOtherUserInfoBeanDao().insert(otherUserInfoBean);

2.2.3. delete一组数据

• 以下代码，其中GreenDaoUtil是获取DaoSession的一个单例工具类。DaoSession可以通过自己的方式获取，但请保持单例。
• 之所以把简单的delete拿出来说，是因为，delete任意一组一对一关联数据其中一个一部分（比如只delete userBean，不delete otherUserInfoBean），另一部分不受影响

GreenDaoUtil.getDaoSession(activity).getUserBeanDao().deleteByKey(user.getId());

2.3. 结语（一对一）

• 关于id的绑定，注意以上示例代码注释
• 关于删除数据，并没有关联删除

3. 一对多

3.1. 注解

@ToMany(referencedJoinProperty = "parentId")

3.2. 示例

• 举例，LeaderBean和MemberBean，每个leader可能对应多个member
• 查看以下代码和注释，可以清楚的了解一对多如何使用（自动注入代码可以适当忽略）
• 以下代码主要包括实体类定义（LeaderBean.java、MemberBean.java），insert一组数据2个部分

3.2.1. 实体类定义

以下示例为rebuild之后的代码

• LeaderBean.java

/**
 * 一对多
 * Created by songyuan on 2017/3/31.
 */
@Entity
public class LeaderBean {
    @Id
    private Long id;
    private String name;

    //此处的leaderId是在MemberBean中定义的一个变量（请看下面的MemberBean.java）
    @ToMany(referencedJoinProperty = "leaderId")
    private List memberBeanList;

    //-------------------------------自动注入代码部分---开始
    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#refresh(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 1942392019)
    public void refresh() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.refresh(this);
    }

    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#update(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 713229351)
    public void update() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.update(this);
    }

    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#delete(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 128553479)
    public void delete() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.delete(this);
    }

    /**
     * Resets a to-many relationship, making the next get call to query for a fresh result.
     */
    @Generated(hash = 73665005)
    public synchronized void resetMemberBeanList() {
        memberBeanList = null;
    }

    /**
     * To-many relationship, resolved on first access (and after reset).
     * Changes to to-many relations are not persisted, make changes to the target entity.
     */
    @Generated(hash = 1515955432)
    public List getMemberBeanList() {
        if (memberBeanList == null) {
            final DaoSession daoSession = this.daoSession;
            if (daoSession == null) {
                throw new DaoException("Entity is detached from DAO context");
            }
            MemberBeanDao targetDao = daoSession.getMemberBeanDao();
            List memberBeanListNew = targetDao._queryLeaderBean_MemberBeanList(id);
            synchronized (this) {
                if (memberBeanList == null) {
                    memberBeanList = memberBeanListNew;
                }
            }
        }
        return memberBeanList;
    }

    /**
     * Used for active entity operations.
     */
    @Generated(hash = 703242250)
    private transient LeaderBeanDao myDao;
    /**
     * Used to resolve relations
     */
    @Generated(hash = 2040040024)
    private transient DaoSession daoSession;

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Long getId() {
        return this.id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    @Generated(hash = 590590377)
    public LeaderBean(Long id, String name) {
        this.id = id;
        this.name = name;
    }

    @Generated(hash = 1761610276)
    public LeaderBean() {
    }

    /** called by internal mechanisms, do not call yourself. */
    @Generated(hash = 1648395956)
    public void __setDaoSession(DaoSession daoSession) {
        this.daoSession = daoSession;
        myDao = daoSession != null ? daoSession.getLeaderBeanDao() : null;
    }

    //-------------------------------自动注入代码部分---结束
    @Override
    public String toString() {
        String memberBeanListStr = "";
        if (getMemberBeanList().size() > 0) {
            for (MemberBean memberBean : getMemberBeanList()) {
                memberBeanListStr = memberBeanListStr + memberBean.toString() + ";";
            }
        }else{
            memberBeanListStr = "null";
        }


        return "LeaderBean{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", memberBeanList=" + memberBeanListStr +
                '}';
    }
}

• MemberBean.java

/**
 * Created by songyuan on 2017/3/31.
 */
@Entity
public class MemberBean {
    @Id
    private Long id;

    //此处自定义leaderId，用于和LeaderBean对应
    private Long leaderId;

    private String name;

    //-------------------------------自动注入代码部分---开始
    public String getName() {
        return this.name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Long getLeaderId() {
        return this.leaderId;
    }
    public void setLeaderId(Long leaderId) {
        this.leaderId = leaderId;
    }
    public Long getId() {
        return this.id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    @Generated(hash = 1935793106)
    public MemberBean(Long id, Long leaderId, String name) {
        this.id = id;
        this.leaderId = leaderId;
        this.name = name;
    }
    @Generated(hash = 1592035565)
    public MemberBean() {
    }
    //-------------------------------自动注入代码部分---结束

    @Override
    public String toString() {
        return "MemberBean{" +
                "id=" + id +
                ", leaderId=" + leaderId +
                ", name='" + name + '\'' +
                '}';
    }
}

3.2.2. insert一组数据

for (int i = 0; i < 2; i++) {
    LeaderBean leader = new LeaderBean();
    leader.setName("张吃啥" + (int) (Math.random() * 1000));

    GreenDaoUtil.getDaoSession(activity).getLeaderBeanDao().insert(leader);

    for (int j = 0; j < 3; j++) {
        MemberBean memberBean = new MemberBean();

        //setLeaderId，值为其所属的leader的id（leaderBean保存完成后，缓存即可获取到数据库中生成的主键id）
        memberBean.setLeaderId(leader.getId());
        memberBean.setName("赵小" + (int) (Math.random() * 1000));

        GreenDaoUtil.getDaoSession(activity).getMemberBeanDao().insert(memberBean);
    }
}

3.3. 结语（一对多）

• 关于id的绑定，注意以上示例代码注释
• delete一个LeaderBean数据，对应的MemberBean数据不会被删除（同一对一的效果）

4. 多对多

4.1. 注解

@JoinEntity(entity = TeacherJoinStudentBean.class,
            sourceProperty = "tId",
            targetProperty = "sId")

4.2. 示例

• 举例，TeacherBean和StudentBean，每个teacher可能对应多个student，每个student也可能对应多个teacher，就如同大学的选修课
• 多对多的实现关键是一个关系绑定类（TeacherJoinStudentBean.java），这个类中只有变量teacherId和studentId，用来记录绑定的关系
• 查看以下代码和注释，可以清楚的了解多对多如何使用（自动注入代码可以适当忽略）
• 以下代码主要包括实体类定义（TeacherBean.java、StudentBean.java），绑定类定义（TeacherJoinStudentBean.java），insert一组数据3个部分

4.2.1. 实体类定义

以下示例为rebuild之后的代码

• TeacherBean.java

@Entity
public class TeacherBean {
    @Id
    private Long id;

    //entity指的是绑定类
    //sourceProperty填写绑定类中标示自身的id，此处为tId，指TeacherBean的id
    //targetProperty填写绑定类中标示关联类的id，此处为sId，指StudentBean的id
    @ToMany
    @JoinEntity(entity = TeacherJoinStudentBean.class,
            sourceProperty = "tId",
            targetProperty = "sId")
    private List studentBeanList;

    //-------------------------------自动注入代码部分---开始
    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#refresh(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 1942392019)
    public void refresh() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.refresh(this);
    }

    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#update(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 713229351)
    public void update() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.update(this);
    }

    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#delete(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 128553479)
    public void delete() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.delete(this);
    }

    /**
     * Resets a to-many relationship, making the next get call to query for a fresh result.
     */
    @Generated(hash = 747728825)
    public synchronized void resetStudentBeanList() {
        studentBeanList = null;
    }

    /**
     * To-many relationship, resolved on first access (and after reset).
     * Changes to to-many relations are not persisted, make changes to the target entity.
     */
    @Generated(hash = 767851859)
    public List getStudentBeanList() {
        if (studentBeanList == null) {
            final DaoSession daoSession = this.daoSession;
            if (daoSession == null) {
                throw new DaoException("Entity is detached from DAO context");
            }
            StudentBeanDao targetDao = daoSession.getStudentBeanDao();
            List studentBeanListNew = targetDao._queryTeacherBean_StudentBeanList(id);
            synchronized (this) {
                if (studentBeanList == null) {
                    studentBeanList = studentBeanListNew;
                }
            }
        }
        return studentBeanList;
    }

    /**
     * Used for active entity operations.
     */
    @Generated(hash = 121856788)
    private transient TeacherBeanDao myDao;
    /**
     * Used to resolve relations
     */
    @Generated(hash = 2040040024)
    private transient DaoSession daoSession;

    public Long getId() {
        return this.id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    @Generated(hash = 121852154)
    public TeacherBean(Long id) {
        this.id = id;
    }

    @Generated(hash = 1376380279)
    public TeacherBean() {
    }

    /** called by internal mechanisms, do not call yourself. */
    @Generated(hash = 1588249045)
    public void __setDaoSession(DaoSession daoSession) {
        this.daoSession = daoSession;
        myDao = daoSession != null ? daoSession.getTeacherBeanDao() : null;
    }
    //-------------------------------自动注入代码部分---结束

    @Override
    public String toString() {
        return "TeacherBean{" +
                "id=" + id +
                ", studentBeanList=" + (getStudentBeanList().size() == 0 ? "null" : getStudentBeanListStr()) +
                '}';
    }

    private String getStudentBeanListStr() {
        String studentBeanListStr = "";
        for (StudentBean studentBean : getStudentBeanList()) {
            studentBeanListStr = studentBeanListStr + studentBean.toStringStudentBeanOnly() + ";";
        }
        return studentBeanListStr;
    }

    /**
     * 用于student打印时调用
     * 仅打印TeacherBean的属性，不打印关联的student,否则死循环StackOverflowError
     *
     * @return
     */
    public String toStringTeacherBeanOnly() {
        return "TeacherBean{" +
                "id=" + id +
                '}';
    }
}

• StudentBean.java

@Entity
public class StudentBean {
    @Id
    private Long id;

    //entity指的是绑定类
    //sourceProperty填写绑定类中标示自身的id，此处为sId，指StudentBean的id
    //targetProperty填写绑定类中标示关联类的id，此处为tId，指TeacherBean的id
    @ToMany
    @JoinEntity(entity = TeacherJoinStudentBean.class,
            sourceProperty = "sId",
            targetProperty = "tId")
    private List teacherBeanList;

    //-------------------------------自动注入代码部分---开始
    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#refresh(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 1942392019)
    public void refresh() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.refresh(this);
    }

    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#update(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 713229351)
    public void update() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.update(this);
    }

    /**
     * Convenient call for {@link org.greenrobot.greendao.AbstractDao#delete(Object)}.
     * Entity must attached to an entity context.
     */
    @Generated(hash = 128553479)
    public void delete() {
        if (myDao == null) {
            throw new DaoException("Entity is detached from DAO context");
        }
        myDao.delete(this);
    }

    /**
     * Resets a to-many relationship, making the next get call to query for a fresh result.
     */
    @Generated(hash = 832141143)
    public synchronized void resetTeacherBeanList() {
        teacherBeanList = null;
    }

    /**
     * To-many relationship, resolved on first access (and after reset).
     * Changes to to-many relations are not persisted, make changes to the target entity.
     */
    @Generated(hash = 299074847)
    public List getTeacherBeanList() {
        if (teacherBeanList == null) {
            final DaoSession daoSession = this.daoSession;
            if (daoSession == null) {
                throw new DaoException("Entity is detached from DAO context");
            }
            TeacherBeanDao targetDao = daoSession.getTeacherBeanDao();
            List teacherBeanListNew = targetDao._queryStudentBean_TeacherBeanList(id);
            synchronized (this) {
                if (teacherBeanList == null) {
                    teacherBeanList = teacherBeanListNew;
                }
            }
        }
        return teacherBeanList;
    }

    /**
     * Used for active entity operations.
     */
    @Generated(hash = 1251043925)
    private transient StudentBeanDao myDao;
    /**
     * Used to resolve relations
     */
    @Generated(hash = 2040040024)
    private transient DaoSession daoSession;

    public Long getId() {
        return this.id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    @Generated(hash = 881285408)
    public StudentBean(Long id) {
        this.id = id;
    }

    @Generated(hash = 2097171990)
    public StudentBean() {
    }

    /** called by internal mechanisms, do not call yourself. */
    @Generated(hash = 2072577263)
    public void __setDaoSession(DaoSession daoSession) {
        this.daoSession = daoSession;
        myDao = daoSession != null ? daoSession.getStudentBeanDao() : null;
    }
    //-------------------------------自动注入代码部分---结束

    @Override
    public String toString() {
        String teacherBeanListStr = "";
        if (getTeacherBeanList().size() > 0) {
            for (TeacherBean teacherBean : getTeacherBeanList()) {
                teacherBeanListStr = teacherBeanListStr + teacherBean.toStringTeacherBeanOnly() + ";";
            }
        } else {
            teacherBeanListStr = "null";
        }

        return "StudentBean{" +
                "id=" + id +
                ", teacherBeanList=" + (getTeacherBeanList().size() == 0 ? "null" : getTeacherBeanListStr()) +
                '}';
    }

    private String getTeacherBeanListStr() {
        String teacherBeanListStr = "";
        for (TeacherBean teacherBean : getTeacherBeanList()) {
            teacherBeanListStr = teacherBeanListStr + teacherBean.toStringTeacherBeanOnly() + ";";
        }
        return teacherBeanListStr;
    }

    /**
     * 用于teacher打印时调用
     * 仅打印StudentBean的属性，不打印关联的teacher,否则死循环StackOverflowError
     *
     * @return
     */
    public String toStringStudentBeanOnly() {
        return "StudentBean{" +
                "id=" + id +
                '}';
    }
}

4.2.2. 绑定类定义

• TeacherJoinStudentBean.java

绑定类，包含teacher的id和student的id

@Entity
public class TeacherJoinStudentBean {
    @Id
    private Long id;
    private Long tId;
    private Long sId;

    //-------------------------------自动注入代码部分---开始
    public Long getSId() {
        return this.sId;
    }
    public void setSId(Long sId) {
        this.sId = sId;
    }
    public Long getTId() {
        return this.tId;
    }
    public void setTId(Long tId) {
        this.tId = tId;
    }
    public Long getId() {
        return this.id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    @Generated(hash = 998000662)
    public TeacherJoinStudentBean(Long id, Long tId, Long sId) {
        this.id = id;
        this.tId = tId;
        this.sId = sId;
    }
    @Generated(hash = 1542025906)
    public TeacherJoinStudentBean() {
    }
    //-------------------------------自动注入代码部分---结束
}

4.2.3. insert一组数据

//2个教师和3个学生的关系
//教师1，带学生1、2
//教师2，带学生1、3
//学生1，选修教师1和教师2的课

List teacherList = new ArrayList();
for (long i = 1; i < 3; i++) {
    TeacherBean teacherBean = new TeacherBean();
    teacherBean.setId(i);
    teacherList.add(teacherBean);
}
GreenDaoUtil.getDaoSession(activity).getTeacherBeanDao().insertInTx(teacherList);

List studentList = new ArrayList();
for (long j = 1; j < 4; j++) {
    StudentBean studentBean = new StudentBean();
    studentBean.setId(j);
    studentList.add(studentBean);
}
GreenDaoUtil.getDaoSession(activity).getStudentBeanDao().insertInTx(studentList);

List teacherJoinStudentList = new ArrayList();
//教师1带学生1、2
TeacherJoinStudentBean teacherJoinStudentBean1 = new TeacherJoinStudentBean(null,1l,1l);
teacherJoinStudentList.add(teacherJoinStudentBean1);

TeacherJoinStudentBean teacherJoinStudentBean2 = new TeacherJoinStudentBean(null,1l,2l);
teacherJoinStudentList.add(teacherJoinStudentBean2);

//教师2带学生1、3
TeacherJoinStudentBean teacherJoinStudentBean3 = new TeacherJoinStudentBean(null,2l,1l);
teacherJoinStudentList.add(teacherJoinStudentBean3);

TeacherJoinStudentBean teacherJoinStudentBean4 = new TeacherJoinStudentBean(null,2l,3l);
teacherJoinStudentList.add(teacherJoinStudentBean4);

GreenDaoUtil.getDaoSession(activity).getTeacherJoinStudentBeanDao().insertInTx(teacherJoinStudentList);

4.3. 结语（多对多）

• 关于id的绑定，注意以上示例代码注释
• 说实话多对多比较坑，感觉没什么使用的必要，可能我还没遇到能用到的项目，如果你有好的例子，欢迎留言链接