GreenDao 3，android适配方案
@Property(nameInDb = “name”)
private String name=“Tom”;
GreenDao 3.3.0版本 设置默认值
默认GreenDao 是没有默认值得,网上说作者不屑于设置,网上搜索后,有很多是修改自动生成的xxxDao 里面的 createTable 中的建表SQL语句
/** Creates the underlying database table. */
public static void createTable(Database db, boolean ifNotExists) {
String constraint = ifNotExists? "IF NOT EXISTS ": “”;
db.execSQL("CREATE TABLE " + constraint + ““USER” (” + //
“”_id" INTEGER PRIMARY KEY AUTOINCREMENT ," + // 0: id
““NAME” TEXT,” + // 1: name
““AGE” INTEGER NOT NULL ,” + // 2: age
““SEX” TEXT,” + // 3: sex
““HEIGHT” INTEGER NOT NULL ,” + // 4: height
““WEIGHT” TEXT);”); // 5: weight
}
也许由于版本的不同,反正3.3没有成功,Android Studio 执行Make Project后还原成原先建表语句,还有人说是修改实体类
@Entity
public class User {
@Id(autoincrement = true)
private Long id;
private String name=“Tom”;
private int age=0;
private String sex;
private int height;
private String weight;
这里有一个坑,这样的方式是可行的,但是如果你这里修改后,去观察UserDao中的建表语句,还是和之前一样是没有变化的.并没有带上 Default 默认值
这样修改后,在插入一条数据,不带默认值的字段赋值后查看数据表,就会发现默认值已经有了,但是UserDao的建表语句还是原来的
@Transient 注解
该注解用于当实体类中有字段不添加到数据表时使用
@Entity
public class User implements Serializable {
@Transient
private static final long serialVersionUID = 1L;
@Id(autoincrement = true)
private Long id
实体类实现 Serializable 报错
这个时候添加一行
@Transient
private static final long serialVersionUID = 1L;
DaoMaster DaoSession 数据操作和表管理
按照上面操作后Build> make project后再自动生成Dao的时候还会生成
-
DaoMaster 建表注册管理表
-
DaoSession 对表进行增删改查
public class GreenDBManager implements IDBManager {
private static final String DB_NAME = “User.db”; //数据库名
private DaoSession mDaoSession;
//private UserTableManager mUserTableManager;
private TablesComponent mTablesComponent;
private DaoMaster daoMaster;
public GreenDBManager init(Application application, String dbName) {
Integer dbVersion = DaoMaster.SCHEMA_VERSION;
mApplication = application;
Class>[] classes = new Class[]{UserDao.class, UserListDao.class};
//DBUpdateOpenHelper对DaoMaster进行初始化，这样就可以实现数据库升级时的数据迁移
DBUpdateOpenHelper updateOpenHelper = new DBUpdateOpenHelper(application, dbName, mclasses);
daoMaster = new DaoMaster(updateOpenHelper.getWritableDatabase());
//9.0的数据库默认启用了wal，用低版本的sqlite工具是无法查看的，想要兼容可以禁用wal
updateOpenHelper.getWritableDatabase().disableWriteAheadLogging();//启用 enableWriteAheadLogging
mDaoSession = daoMaster.newSession();
//查看数据库更新版本时数据迁移的log
MigrationHelper.DEBUG = false;
//数据库增删改查时的log
QueryBuilder.LOG_SQL = false;
QueryBuilder.LOG_VALUES = false;
//清空缓存
mDaoSession.clear();
return this;
}
@Override
public DaoSession getDaoSession() {
if (mDaoSession==null){
mDaoSession=daoMaster.newSession();
}
return mDaoSession;
}
在Application 里面初始化init后,就可通过 getDaoSession 对所有表进行操作处理了
DBUpdateOpenHelper.java
public class DBUpdateOpenHelper extends DaoMaster.OpenHelper {
Class>[] mDaoClasses;
public DBUpdateOpenHelper(Context context, String name, Class>… daoClasses) {
super(context, name);
mDaoClasses=daoClasses;
}
public DBUpdateOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, Class>… daoClasses) {
super(context, name, factory);
mDaoClasses=daoClasses;
}
@Override
public void onCreate(Database db) {
DaoMaster.createAllTables(db, false);
}
@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
//把需要管理的数据库表DAO作为最后一个参数传入到方法中
MigrationHelper.migrate(db, new MigrationHelper.ReCreateAllTableListener() {
@Override
public void onCreateAllTables(Database db, boolean ifNotExists) {
DaoMaster.createAllTables(db, ifNotExists);
}
@Override
public void onDropAllTables(Database db, boolean ifExists) {
DaoMaster.dropAllTables(db, ifExists);
}
}, mDaoClasses);
}
}
MigrationHelper.java 用于数据库升级时数据迁移
package com.zk.greendb.helper;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.text.TextUtils;
import android.util.Log;
import org.greenrobot.greendao.AbstractDao;
import org.greenrobot.greendao.database.Database;
import org.greenrobot.greendao.database.StandardDatabase;
import org.greenrobot.greendao.internal.DaoConfig;
import java.lang.ref.WeakReference;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
-
用于数据库升级时数据迁移
-
from https://github.com/yuweiguocn/GreenDaoUpgradeHelper
-
please call {@link #migrate(SQLiteDatabase, Class[])} or {@link #migrate(Database, Class[])}
*/
public class MigrationHelper {
public static boolean DEBUG = false;
private static final String TAG= MigrationHelper.class.getSimpleName();
private static final String SQLITE_MASTER = “sqlite_master”;
private static final String SQLITE_TEMP_MASTER = “sqlite_temp_master”;
private static WeakReference weakListener;
public interface ReCreateAllTableListener{
void onCreateAllTables(Database db, boolean ifNotExists);
void onDropAllTables(Database db, boolean ifExists);
}
public static void migrate(SQLiteDatabase db, Class>… daoClasses) {
printLog("【The Old Database Version】" + db.getVersion());
Database database = new StandardDatabase(db);
migrate(database, daoClasses);
}
public static void migrate(SQLiteDatabase db, MigrationHelper.ReCreateAllTableListener listener, Class>… daoClasses) {
weakListener = new WeakReference<>(listener);
migrate(db, daoClasses);
}
public static void migrate(Database database, MigrationHelper.ReCreateAllTableListener listener, Class>… daoClasses) {
weakListener = new WeakReference<>(listener);
migrate(database, daoClasses);
}
public static void migrate(Database database, Class>… daoClasses) {
printLog("【Generate temp table】start");
generateTempTables(database, daoClasses);
printLog("【Generate temp table】complete");
MigrationHelper.ReCreateAllTableListener listener = weakListener.get();
if (listener != null) {
listener.onDropAllTables(database, true);
printLog("【Drop all table by listener】");
listener.onCreateAllTables(database, false);
printLog("【Create all table by listener】");
} else {
dropAllTables(database, true, daoClasses);
createAllTables(database, false, daoClasses);
}
printLog("【Restore data】start");
restoreData(database, daoClasses);
printLog("【Restore data】complete");
}
private static void generateTempTables(Database db, Class>… daoClasses) {
for (int i = 0; i < daoClasses.length; i++) {
String tempTableName = null;
DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);
String tableName = daoConfig.tablename;
if (!isTableExists(db, false, tableName)) {
printLog("【New Table】" + tableName);
continue;
}
try {
tempTableName = daoConfig.tablename.concat("_TEMP");
StringBuilder dropTableStringBuilder = new StringBuilder();
dropTableStringBuilder.append(“DROP TABLE IF EXISTS “).append(tempTableName).append(”;”);
db.execSQL(dropTableStringBuilder.toString());
StringBuilder insertTableStringBuilder = new StringBuilder();
insertTableStringBuilder.append("CREATE TEMPORARY TABLE ").append(tempTableName);
insertTableStringBuilder.append(" AS SELECT * FROM “).append(tableName).append(”;");
db.execSQL(insertTableStringBuilder.toString());
printLog("【Table】" + tableName +"\n —Columns–>"+getColumnsStr(daoConfig));
printLog("【Generate temp table】" + tempTableName);
} catch (SQLException e) {
Log.e(TAG, “【Failed to generate temp table】” + tempTableName, e);
}
}
}
private static boolean isTableExists(Database db, boolean isTemp, String tableName) {
if (db == null || TextUtils.isEmpty(tableName)) {
return false;
}
String dbName = isTemp ? SQLITE_TEMP_MASTER : SQLITE_MASTER;
String sql = “SELECT COUNT(*) FROM " + dbName + " WHERE type = ? AND name = ?”;
Cursor cursor=null;
int count = 0;
try {
cursor = db.rawQuery(sql, new String[]{“table”, tableName});
if (cursor == null || !cursor.moveToFirst()) {
return false;
}
count = cursor.getInt(0);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (cursor != null)
cursor.close();
}
return count > 0;
}
private static String getColumnsStr(DaoConfig daoConfig) {
if (daoConfig == null) {
return “no columns”;
}
StringBuilder builder = new StringBuilder();
for (int i = 0; i < daoConfig.allColumns.length; i++) {
builder.append(daoConfig.allColumns[i]);
builder.append(",");
}
if (builder.length() > 0) {
builder.deleteCharAt(builder.length() - 1);
}
return builder.toString();
}
public static void dropAllTables(Database db, boolean ifExists, Class>… daoClasses) {
reflectMethod(db, “dropTable”, ifExists, daoClasses);
printLog("【Drop all table by reflect】");
}
public static void createAllTables(Database db, boolean ifNotExists, Class>… daoClasses) {
reflectMethod(db, “createTable”, ifNotExists, daoClasses);
printLog("【Create all table by reflect】");
}
/**
- dao class already define the sql exec method, so just invoke it
*/
private static void reflectMethod(Database db, String methodName, boolean isExists, Class>… daoClasses) {
if (daoClasses.length < 1) {
return;
}
try {
最后
由于题目很多整理答案的工作量太大，所以仅限于提供知识点，详细的很多问题和参考答案我都整理成了 PDF文件，需要的小伙伴可以私信我【面试】免费领取或者点击GitHub免费获取！
- dao class already define the sql exec method, so just invoke it
*/
private static void reflectMethod(Database db, String methodName, boolean isExists, Class>… daoClasses) {
if (daoClasses.length < 1) {
return;
}
try {
最后
由于题目很多整理答案的工作量太大，所以仅限于提供知识点，详细的很多问题和参考答案我都整理成了 PDF文件，需要的小伙伴可以私信我【面试】免费领取或者点击GitHub免费获取！
[外链图片转存中…(img-hbzzUS9w-1646395359901)]
[外链图片转存中…(img-P0QkcNUM-1646395359902)]
