1、数据库升级
原理:创建临时表-->删除原表-->创建新表-->复制临时表数据到新表并删除临时表;这样就实现数据库表的更新了
新建一个数据库更新辅助类 MigrationHelper
public class MigrationHelper {
private static final String CONVERSION_CLASS_NOT_FOUND_EXCEPTION = "MIGRATION HELPER - CLASS DOESN'T MATCH WITH THE CURRENT PARAMETERS";
private static MigrationHelper instance;
public static MigrationHelper getInstance() {
if (instance == null) {
instance = new MigrationHelper();
}
return instance;
}
public void migrate(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
generateTempTables(db, daoClasses);
DaoMaster.dropAllTables(db, true);
DaoMaster.createAllTables(db, false);
restoreData(db, daoClasses);
}
/**
* 生成临时列表
*
* @param db
* @param daoClasses
*/
private void generateTempTables(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
for (int i = 0; i < daoClasses.length; i++) {
DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);
String divider = "";
String tableName = daoConfig.tablename;
String tempTableName = daoConfig.tablename.concat("_TEMP");
ArrayList<String> properties = new ArrayList<>();
StringBuilder createTableStringBuilder = new StringBuilder();
createTableStringBuilder.append("CREATE TABLE ").append(tempTableName).append(" (");
for (int j = 0; j < daoConfig.properties.length; j++) {
String columnName = daoConfig.properties[j].columnName;
if (getColumns(db, tableName).contains(columnName)) {
properties.add(columnName);
String type = null;
try {
type = getTypeByClass(daoConfig.properties[j].type);
} catch (Exception exception) {
exception.printStackTrace();
}
createTableStringBuilder.append(divider).append(columnName).append(" ").append(type);
if (daoConfig.properties[j].primaryKey) {
createTableStringBuilder.append(" PRIMARY KEY");
}
divider = ",";
}
}
createTableStringBuilder.append(");");
db.execSQL(createTableStringBuilder.toString());
StringBuilder insertTableStringBuilder = new StringBuilder();
insertTableStringBuilder.append("INSERT INTO ").append(tempTableName).append(" (");
insertTableStringBuilder.append(TextUtils.join(",", properties));
insertTableStringBuilder.append(") SELECT ");
insertTableStringBuilder.append(TextUtils.join(",", properties));
insertTableStringBuilder.append(" FROM ").append(tableName).append(";");
db.execSQL(insertTableStringBuilder.toString());
}
}
/**
* 存储新的数据库表 以及数据
*
* @param db
* @param daoClasses
*/
private void restoreData(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
for (int i = 0; i < daoClasses.length; i++) {
DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);
String tableName = daoConfig.tablename;
String tempTableName = daoConfig.tablename.concat("_TEMP");
ArrayList<String> properties = new ArrayList();
for (int j = 0; j < daoConfig.properties.length; j++) {
String columnName = daoConfig.properties[j].columnName;
if (getColumns(db, tempTableName).contains(columnName)) {
properties.add(columnName);
}
}
StringBuilder insertTableStringBuilder = new StringBuilder();
insertTableStringBuilder.append("INSERT INTO ").append(tableName).append(" (");
insertTableStringBuilder.append(TextUtils.join(",", properties));
insertTableStringBuilder.append(") SELECT ");
insertTableStringBuilder.append(TextUtils.join(",", properties));
insertTableStringBuilder.append(" FROM ").append(tempTableName).append(";");
StringBuilder dropTableStringBuilder = new StringBuilder();
dropTableStringBuilder.append("DROP TABLE ").append(tempTableName);
db.execSQL(insertTableStringBuilder.toString());
db.execSQL(dropTableStringBuilder.toString());
}
}
private String getTypeByClass(Class<?> type) throws Exception {
if (type.equals(String.class)) {
return "TEXT";
}
if (type.equals(Long.class) || type.equals(Integer.class) || type.equals(long.class)) {
return "INTEGER";
}
if (type.equals(Boolean.class)) {
return "BOOLEAN";
}
Exception exception = new Exception(CONVERSION_CLASS_NOT_FOUND_EXCEPTION.concat(" - Class: ").concat(type.toString()));
exception.printStackTrace();
throw exception;
}
private List<String> getColumns(Database db, String tableName) {
List<String> columns = new ArrayList<>();
Cursor cursor = null;
try {
cursor = db.rawQuery("SELECT * FROM " + tableName + " limit 1", null);
if (cursor != null) {
columns = new ArrayList<>(Arrays.asList(cursor.getColumnNames()));
}
} catch (Exception e) {
Log.v(tableName, e.getMessage(), e);
e.printStackTrace();
} finally {
if (cursor != null)
cursor.close();
}
return columns;
}
}
新建一个MyOpenHelper类:
public class MyOpenHelper extends DaoMaster.OpenHelper {
public MyOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
super(context, name, factory);
}
/**
* 数据库升级
* @param db
* @param oldVersion
* @param newVersion
*/
@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
//操作数据库的更新 有几个表升级都可以传入到下面
Log.i("version", oldVersion + "---先前和更新之后的版本---" + newVersion);
if (oldVersion < newVersion) {
Log.i("version", oldVersion + "---先前和更新之后的版本---" + newVersion);
MigrationHelper.getInstance().migrate(db, BookDao.class);
//更改过的实体类(新增的不用加) 更新UserDao文件 可以添加多个 XXDao.class 文件
// MigrationHelper.getInstance().migrate(db, UserDao.class,XXDao.class);
}
//MigrationHelper.getInstance().migrate(db,StudentDao.class);
}
}
同时DBManager中的getDaoMaster方法要更换成:
/**
* 获取DaoMaster
*
* 判断是否存在数据库,如果没有则创建数据库
* @param context
* @return
*/
public static DaoMaster getDaoMaster(Context context) {
if (null == mDaoMaster) {
synchronized (DbManager.class) {
if (null == mDaoMaster) {
MyOpenHelper helper = new MyOpenHelper(context,DB_NAME,null);
mDaoMaster = new DaoMaster(helper.getWritableDatabase());
}
}
}
return mDaoMaster;
}
测试一下,在Book类中增加一个属性publishHouse,将build.gradle里面schemaVersion改为 2 ,运行后查看数据库可以看到增加了新字段,同时旧数据依然存在。
2、检测表字段是否存在
private boolean hasColumn(SQLiteDatabase db, String tableName, String column) {
if (TextUtils.isEmpty(tableName) || TextUtils.isEmpty(column)) {
return false;
}
Cursor cursor = null;
try {
cursor = db.query(tableName, null, null, null, null, null, null);
if (null != cursor && cursor.getColumnIndex(column) != -1) {
return true;
}
} finally {
if (null != cursor) {
cursor.close();
}
}
return false;
}
3、复杂表结构
上一篇在讲注解时讲到@ToOne和@ToMany ,就是在创建对象时指明表关系的。
(1)@ToOne 建立一对一 ( 1 : 1) 关系
@Entity
public class Order {
@Id
private Long id;
private long customerId;
@ToOne(joinProperty = "customerId")
private Customer customer;
}
@Entity
public class Customer {
@Id
private Long id;
}
(2)@ToMany 建立一对多 (1:N ) 关系
@Entity
public class Customer {
@Id
private Long id;
@ToMany(referencedJoinProperty = "customerId")
@OrderBy("date ASC")
private List<Order> orders;
}
@Entity
public class Order {
@Id private Long id;
private Date date;
private long customerId;
}
(3)@JoinEntity 建立多对多(N : M)关系
@Entity
public class Product {
@Id private Long id;
@ToMany
@JoinEntity(
entity = JoinProductsWithOrders.class,
sourceProperty = "productId",
targetProperty = "orderId"
)
private List<Order> ordersWithThisProduct;
}
@Entity
public class JoinProductsWithOrders {
@Id private Long id;
private Long productId;
private Long orderId;
}
@Entity
public class Order {
@Id private Long id;
}
4、复杂查询
(1)条件查询
//方法一:
List<User> userlist = userDao.queryRaw("where AGE>?","10");//查询年龄大于10的用户
//方法二:
List<User> userlist = userDao.queryBuilder().where(UserDao.Properties.Age.gt("10")).list();
(2)排序
// order by last name
queryBuilder.orderAsc(Properties.LastName);
// in reverse
queryBuilder.orderDesc(Properties.LastName);
// order by last name and year of birth
queryBuilder.orderAsc(Properties.LastName).orderDesc(Properties.YearOfBirth);
(3)分页
//limit(int) : 限制查询返回的结果的数量。
//offset(int): 设置起始位置
// 从第二条记录开始查询5条记录
List<User> list = userDao.queryBuilder()
.offset(2)
.limit(5)
.list();
(4)懒加载
LazyList<User> lazyList = userDao.queryBuilder().listLazy();
for (User u:lazyList) {
Log.i(TAG, "用户名:"+u.getName());
}
//不再使用时必须关闭,否则会导致数据库游标未关闭,从而导致内存泄漏
lazyList.close();
(5)多表查询
QueryBuilder<User> queryBuilder = userDao.queryBuilder();
queryBuilder.join(Address.class, AddressDao.Properties.userId)
.where(AddressDao.Properties.Street.eq("Sesame Street"));
List<User> users = queryBuilder.list();
5、数据库加密
greenDAO 支持 SQLCipher 直接绑定
引入依赖:
compile 'net.zetetic:android-database-sqlcipher:3.5.7@aar'
初始化数据库
DevOpenHelper helper = new DevOpenHelper(this, "test.db");
Database db = helper.getEncryptedWritableDb("password");
daoSession = new DaoMaster(db).newSession();
其他操作正常使用