简便数据库——ORMLite框架

时间:2022-01-15 20:49:22

一、创建DataBase

//使用 Singleton 避免產生多個實例(instance),要注意 thread safe 這邊使用雙重鎖定(Double-checked locking)
使用 TableUtils 類別建立及刪除表格 //第一步继承 OrmLiteSqliteOpenHelper
public class DatabaseHelper extends OrmLiteSqliteOpenHelper { //版本号
private static final int DATABASE_VERSION = 1;
//版本名
private static final String DATABASE_NAME = "Demo";
//单例
private static DatabaseHelper instance; private DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
} //运用单例,加上双层线程锁,避免多创建DataBase
public static synchronized DatabaseHelper getHelper(Context context) {
context = context.getApplicationContext();
if (instance == null) {
synchronized (DatabaseHelper.class) {
if (instance == null)
instance = new DatabaseHelper(context);
}
}
return instance;
} //删除并重新创建
@Override
public void onUpgrade(SQLiteDatabase database, ConnectionSource connectionSource, int oldVersion, int newVersion) {
try {
TableUtils.dropTable(connectionSource, User.class, true);
TableUtils.dropTable(connectionSource, Group.class, true);
onCreate(database, connectionSource);
} catch (SQLException e) {
e.printStackTrace();
}
} //创建 表格
@Override
public void onCreate(SQLiteDatabase database, ConnectionSource connectionSource) {
try {
TableUtils.createTable(connectionSource, User.class);
TableUtils.createTable(connectionSource, Group.class);
} catch (SQLException e) {
e.printStackTrace();
}
}
}

DataBaseHelper

二、创建相应的JavaBean

public class User {
//注意事项:一定要加上@DatabaseField 说明这是表中的字段,这语句就是sql语句中设定主键,外键之类的。。。
@DatabaseField(generatedId = true)
private int id;
@DatabaseField
private String name;
@DatabaseField
private String psd; public int getId() {
return id;
} public void setId(int id) {
this.id = id;
} public String getName() {
return name;
} public void setName(String name) {
this.name = name;
} public String getPsd() {
return psd;
} public void setPsd(String psd) {
this.psd = psd;
}
}

User

三、创建对DataBase的操作(这里创建操作的泛型,就是所有Dao类型都能使用)

//承接DatBaseHelper
....
//参数是Class类型
private HashMap<String,RuntimeExceptionDao> mRuntimeDaos = new HashMap<>(); public RuntimeExceptionDao getRuntimeDao(Class bean){ RuntimeExceptionDao dao = null;
String className = bean.getSimpleName();
//防止重新创建Dao
if (mRuntimeDaos.containsKey(className)){
dao = mRuntimeDaos.get(className);
}
else {
//重要的地方,如何创建Dao
dao = super.getRuntimeExceptionDao(bean);
}
return dao;
}

DataBase

四、创建对应的Dao(处理JavaBean与DataBase之间的操作)

public class UserDao {
private RuntimeExceptionDao mRuntimeDao;
//构造方法中获取Dao,用来操作数据库
public UserDao(Context context) {
DataBaseHelper dataBaseHelper = DataBaseHelper.getHelper(context);
mRuntimeDao = dataBaseHelper.getRuntimeDao(User.class);
}
//添加一个User到数据库
public void createUser(User user){
mRuntimeDao.createOrUpdate(user);
}
//从数据库中检索id为?的user
public List<User> queryUser(int id){
List<User> user = null;
try {
user = mRuntimeDao.queryBuilder().where().eq("id",id).query();
} catch (SQLException e) {
e.printStackTrace();
}
return user;
}
//清除数据库
public void clear(){
mRuntimeDao.delete(mRuntimeDao.queryForAll());
}
}

UserDao

五、ORMLite外键引用

创建一个Article类,需要知道这个Article所属的User,那么该怎么办。一般的方法,就是放入这个User的id,但是OrmLite可以放入整个User,这才是正确的面向对象程序。

所以要这么写:

public class Article {
@DatabaseField(generatedId = true)
private int id;
@DatabaseField
private String title;
@DatabaseField
private String content;
//声明这列为外键,不同于常规的数据库 外键设置的是User的id,这里直接将User设定为外键
@DatabaseField(canBeNull = true,foreign = true,columnName = "user_id")
private User user; public String getContent() {
return content;
} public void setContent(String content) {
this.content = content;
} public int getId() {
return id;
} public void setId(int id) {
this.id = id;
} public String getTitle() {
return title;
} public void setTitle(String title) {
this.title = title;
} public User getUser() {
return user;
} public void setUser(User user) {
this.user = user;
}
}

Article

public class ArticleDao {
private RuntimeExceptionDao mRuntimeDao;
private DataBaseHelper mDataBaseHelper;
//构造方法中获取Dao,用来操作数据库
public ArticleDao(Context context) {
mDataBaseHelper = DataBaseHelper.getHelper(context);
mRuntimeDao = mDataBaseHelper.getRuntimeDao(Article.class);
}
//添加一个Article到数据库
public void createUser(Article article){
mRuntimeDao.createOrUpdate(article);
}
//从数据库中检索id为?的Article,经过测试发现 只能获取到User的id,其他内容都是无法获取的
public Article queryArticle(int id){
Article article = null;
article = (Article) mRuntimeDao.queryForId(id);
return article;
}
//所以需要用该方法
public Article getArticleWithUser(int id){
Article article = queryArticle(id);
//获取到的article并没有User这个对象的内容,需要经过这一层赋值。
mDataBaseHelper.getRuntimeDao(User.class).refresh(article.getUser());
return article;
}
//根据user对象获取全部的Article
public List<Article> getArticles(int userId){
List<Article> articles = null;
try {
//发现userId的赋值跟int赋值一样
articles = mRuntimeDao.queryBuilder().where().eq("user_id",userId).query();
} catch (SQLException e) {
e.printStackTrace();
}
return articles;
}
//清除数据库
public void clear(){
mRuntimeDao.delete(mRuntimeDao.queryForAll());
}

ArticleDao

2、在user属性的注解上:@DatabaseField(canBeNull = true, foreign = true, columnName = "user_id", foreignAutoRefresh = true)

添加foreignAutoRefresh =true,这样;当调用queryForId时,拿到Article对象则直接携带了user;

六:关联一个集合

每个User关联一个或多个Article,如果我在User中声明一个Collection<Article> articles,我能否在查询User的时候,一并能够获取到articles的值呢?

在User中添加如下属性,且注解如下:

@ForeignCollectionField
private Collection<Article> articles;

测试代码

User user = new UserDao(getContext()).get(1);
L.e(user.getName());
if (user.getArticles() != null)
for (Article article : user.getArticles())
{
L.e(article.toString());
}

User关联多个Article

注:id的自增是从1开始的 0 0