前面介紹了ormlite操作單張表以及多表之間的一對多（多對一）的關係（請參考android對象關係映射框架ormlite學習之單表操作和android關係映射框架ormlite學習之OneToMany），但是我們還經常會遇到多對多的數據庫表關係，在處理多對多的關係表時，ormlite官方給出的解決方案是通過建立第三張關聯表來解決的。這裏通過這個解決方案來解決我們最後一個關於多對多關係。
我假設的場景是項目（Project）和用戶(User)，即一個用戶參與多個項目，而一個項目又由多個人員進行開發，構成多對多的關係。同樣的對於中間重要的方法類註釋在代碼中。首先同樣給出運行效果圖：
實體用戶類User.java
@DatabaseTable(tableName = "tb_user")
public class User {
//這裏用一個常量來設置屬性的名字，這樣我們在中就可以直接使用該名字
public final static String ID_FIELD_NAME = "user_id";
//用戶編號
@DatabaseField(generatedId=true,columnName=ID_FIELD_NAME)
private int userId;
//用戶名
@DatabaseField
private String userName;
public User() {
//提供無參構造函數，這樣查詢的時候可以返回查詢出來的對象
}
public User( int userId,String userName) {
this.userId = userId;
this.userName = userName;
}
get/set方法
}/**
* 項目類（假設一個用戶參與多個項目，一個項目又由多個用戶參與負責）
* @author leox
*
*/
@DatabaseTable(tableName="tb_project")
public class Project {
public final static String ID_FIELD_NAME = "project_id";
//項目編號
@DatabaseField(generatedId=true,columnName=ID_FIELD_NAME)
private int projectId;
//項目名
@DatabaseField
private String projectName;
public Project() {}
public Project(int projectId, String projectName) {
this.projectId = projectId;
this.projectName = projectName;
}
get/set方法
}
/**
* 用戶項目關聯類
*（用ormlite實現ManyToMany需要在數據庫中建立一張關聯表）
* @author leox
*
*/
@DatabaseTable(tableName="tb_user_project")
public class UserProject {
public final static String USER_ID_FIELD_NAME = "user_id";
public final static String PROJECT_ID_FIELD_NAME = "project_id";
//用戶項目編號
@DatabaseField(generatedId=true)
private int id;
//關聯用戶表
@DatabaseField(foreign = true,columnName=USER_ID_FIELD_NAME)
private User user;
//關聯項目表
@DatabaseField(foreign = true,columnName=PROJECT_ID_FIELD_NAME)
private Project project;
public UserProject(){}
public UserProject(int id, User user, Project project) {
this.id = id;
this.user = user;
this.project = project;
}
get/set方法
}public class DatabaseHelper extends OrmLiteSqliteOpenHelper{
// 數據庫名稱
private static final String DATABASE_NAME = "helloAndroid.db";
// 數據庫version
private static final int DATABASE_VERSION = 1;
private PreparedQuery<Project> projectsForUserQuery = null;
private PreparedQuery<User> usersForProjectQuery = null;
/**
* 包含兩個泛型:
* 第一個泛型表DAO操作的類
* 第二個表示操作類的主鍵類型
*/
private RuntimeExceptionDao<User, Integer> simpleRuntimeUserDao = null;
private RuntimeExceptionDao<Project, Integer> simpleRuntimeProjectDao = null;
private RuntimeExceptionDao<UserProject, Integer> simpleRuntimeUserProjectDao = null;
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase sqliteDatabase, ConnectionSource connectionSource) {
try {
Log.i(DatabaseHelper.class.getName(), "onCreate");
//創建用戶、項目、用戶項目關聯三張表
TableUtils.createTable(connectionSource, UserProject.class);
TableUtils.createTable(connectionSource, User.class);
TableUtils.createTable(connectionSource, Project.class);
} catch (SQLException e) {
Log.e(DatabaseHelper.class.getName(), "Can't create database", e);
throw new RuntimeException(e);
}
}
/**
* 插入一條用戶數據
*/
public void insert(User user){
RuntimeExceptionDao<User, Integer> dao = getSimpleDataUserDao();
//通過實體對象創建在數據庫中創建一條數據，成功返回1，說明插入了一條數據
Log.i("test", "dao = " + dao+" user= "+user);
int returnValue = dao.create(user);
Log.i("test", "插入數據後返回值："+returnValue);
}
/**
* 查詢所有的用戶信息
* @return
*/
public List<User> findAllUser(){
RuntimeExceptionDao<User, Integer> dao = getSimpleDataUserDao();
return dao.queryForAll();
}
public RuntimeExceptionDao<User, Integer> getSimpleDataUserDao() {
if (simpleRuntimeUserDao == null) {
simpleRuntimeUserDao = getRuntimeExceptionDao(User.class);
}
Log.i("test", "simpleRuntimeDao ======= "+simpleRuntimeUserDao);
return simpleRuntimeUserDao;
}
/**
* 這個方法在你的應用升級以及它有一個更高的版本號時調用。所以需要你調整各種數據來適應新的版本
*/
@Override
public void onUpgrade(SQLiteDatabase sqliteDatabase, ConnectionSource connectionSource, int oldVersion,
int newVersion) {
Log.i("test", "更新....");
try {
Log.i(DatabaseHelper.class.getName(), "onUpgrade");
//刪掉舊版本的數據
TableUtils.dropTable(connectionSource, User.class, true);
TableUtils.dropTable(connectionSource, UserProject.class, true);
//創建一個新的版本
onCreate(sqliteDatabase, connectionSource);
} catch (SQLException e) {
Log.e(DatabaseHelper.class.getName(), "Can't drop databases", e);
throw new RuntimeException(e);
}
}
/***************************************以下爲用戶項目關聯操作******************************************/
public RuntimeExceptionDao<UserProject, Integer> getSimpleDataUserProjectDao() {
if (simpleRuntimeUserProjectDao == null) {
simpleRuntimeUserProjectDao = getRuntimeExceptionDao(UserProject.class);
}
Log.i("test", "simpleRuntimeDaodeptdept ======= "+simpleRuntimeUserProjectDao);
return simpleRuntimeUserProjectDao;
}
/**
* 插入一條用戶項目關聯數據
*/
public void insertDept(UserProject dept){
RuntimeExceptionDao<UserProject, Integer> dao = getSimpleDataUserProjectDao();
//通過實體對象創建在數據庫中創建一條數據，成功返回1，說明插入了一條數據
int returnValue = dao.create(dept);
Log.i("test", "插入數據後返回值："+returnValue);
}
/****************以下爲對項目的操作*********************/
public RuntimeExceptionDao<Project, Integer> getSimpleDataProjectDao() {
if (simpleRuntimeProjectDao == null) {
simpleRuntimeProjectDao = getRuntimeExceptionDao(Project.class);
}
Log.i("test", "simpleRuntimeDaodeptdept ======= "+simpleRuntimeProjectDao);
return simpleRuntimeProjectDao;
}
public Project findByDeptId(int projectId){
RuntimeExceptionDao<Project, Integer> dao = getSimpleDataProjectDao();
return dao.queryForId(projectId);
}
/**
* 插入一條項目數據
*/
public void insertProject(Project project){
RuntimeExceptionDao<Project, Integer> dao = getSimpleDataProjectDao();
//通過實體對象創建在數據庫中創建一條數據，成功返回1，說明插入了一條數據
int returnValue = dao.create(project);
Log.i("test", "插入數據後返回值："+returnValue);
}
public List<Project> lookupProjectsForUser(User user) throws SQLException {
RuntimeExceptionDao<Project, Integer> dao = getSimpleDataProjectDao();
if (projectsForUserQuery == null) {
projectsForUserQuery = makePostsForUserQuery();
}
projectsForUserQuery.setArgumentHolderValue(0, user);
return dao.query(projectsForUserQuery);
}
/**
* 查詢某個用戶所對應的項目
*/
private PreparedQuery<Project> makePostsForUserQuery() throws SQLException {
RuntimeExceptionDao<UserProject, Integer> userProjectDao = getSimpleDataUserProjectDao();
RuntimeExceptionDao<Project, Integer> projectDao = getSimpleDataProjectDao();
//創建一個內關聯查詢用戶項目表
QueryBuilder<UserProject, Integer> userProject = userProjectDao.queryBuilder();
//查詢關聯表tb_user_project時返回“project_id”如果沒有該語句，即返回該表所有字段，相當於“select * from 表名”
//拼成sql語句：select project_id from tb_user_project
userProject.selectColumns(UserProject.PROJECT_ID_FIELD_NAME);
//這相當於一個可變的參數，相當於SQL語句中的“？”,這個參數會在後面的操作中指明
SelectArg userSelectArg = new SelectArg();
//設置條件語句（where user_id=?）
userProject.where().eq(UserProject.USER_ID_FIELD_NAME, userSelectArg);
//創建外部查詢項目表
QueryBuilder<Project, Integer> postQb = projectDao.queryBuilder();
//設置查詢條件（where project_id in()）;
postQb.where().in(Project.ID_FIELD_NAME, userProject);
/**
* 這裏返回時完整的sql語句爲
* "SELECT * FROM `tb_project`
* WHERE `project_id` IN (
* SELECT `project_id` FROM `tb_user_project` WHERE `user_id` = ?
* ) "
*/
return postQb.prepare();
}
public List<User> lookupUsersForProject(Project project) throws SQLException {
RuntimeExceptionDao<User, Integer> dao = getSimpleDataUserDao();
if (usersForProjectQuery == null) {
usersForProjectQuery = makeUsersForProjectQuery();
}
usersForProjectQuery.setArgumentHolderValue(0, project);
return dao.query(usersForProjectQuery);
}
/**
* 查詢某個項目的所有負責人
*/
private PreparedQuery<User> makeUsersForProjectQuery() throws SQLException {
RuntimeExceptionDao<UserProject, Integer> userProjectDao = getSimpleDataUserProjectDao();
RuntimeExceptionDao<User, Integer> userDao = getSimpleDataUserDao();
QueryBuilder<UserProject, Integer> userProject = userProjectDao.queryBuilder();
userProject.selectColumns(UserProject.USER_ID_FIELD_NAME);
SelectArg userSelectArg = new SelectArg();
userProject.where().eq(UserProject.PROJECT_ID_FIELD_NAME, userSelectArg);
QueryBuilder<User, Integer> postQb = userDao.queryBuilder();
postQb.where().in(User.ID_FIELD_NAME, userProject);
return postQb.prepare();
}
}
public class MainActivity extends Activity {
Button button1;//數據初始化按鈕
Button button2;//顯示某人蔘與的項目
Button button3;//顯示某項目參與的人員
TextView textView;//用來顯示查詢到的用戶信息
DatabaseHelper helper = new DatabaseHelper(this);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
button1 = (Button)this.findViewById(R.id.main_btn_inputinfo);
button2 = (Button)this.findViewById(R.id.main_project_show);
button3 = (Button)this.findViewById(R.id.main_user_show);
textView = (TextView)this.findViewById(R.id.main_show_user);
//點擊註冊按鈕跳轉到註冊頁面
button1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
//創建第一個用戶
User user1 = new User();
user1.setUserName("張三");
helper.insert(user1);
//創建第一個項目
Project project1 = new Project();
project1.setProjectName("項目一");
helper.insertProject(project1);
//將用戶一和項目一關聯起來
UserProject up1 = new UserProject();
up1.setProject(project1);
up1.setUser(user1);
helper.insertDept(up1);
//創建第二個項目
Project project2 = new Project();
project2.setProjectName("項目二");
helper.insertProject(project2);
//將用戶一和項目二關聯起來(即用戶一參與了項目一和項目二)
UserProject up2 = new UserProject();
up2.setProject(project2);
up2.setUser(user1);
helper.insertDept(up2);
//創建第二個用戶
User user2 = new User();
user2.setUserName("李四");
helper.insert(user2);
//將用戶二和項目二關聯起來(即項目二由用戶一和用戶二共同開發)
UserProject up3 = new UserProject();
up3.setProject(project2);
up3.setUser(user2);
helper.insertDept(up3);
Toast.makeText(MainActivity.this, "初始化成功！", Toast.LENGTH_LONG);
}
});
//點擊顯示某個人負責的項目按鈕時的操作（將前面添加的用戶一所對應的項目顯示出來）
button2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
List<User> users = helper.findAllUser();
if(users.size()>0){
String str = users.get(0).getUserName()+" 參與的項目：";
try {
List<Project> proList = helper.lookupProjectsForUser(users.get(0));
if(proList.size()>0){
for(Project p:proList){
//Log.i("test", "項目名："+p.getProjectName());
str+=p.getProjectName()+",";
}
}
textView.setText(str);
} catch (SQLException e) {
e.printStackTrace();
}
}
}
});
//點擊顯示某項目負責人按鈕時的操作（將項目二的負責人信息顯示出來）
button3.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Project project = helper.findByDeptId(2);
if(project!=null){
String str = project.getProjectName()+" 參與的人員有：";
try {
List<User> userList = helper.lookupUsersForProject(project);
if(userList.size()>0){
for(User u:userList){
//Log.i("test", "項目名："+p.getProjectName());
str+=u.getUserName()+",";
}
}
textView.setText(str);
} catch (SQLException e) {
e.printStackTrace();
}
}
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}