数据库升级:
其实就是对数据库的本身进行增删改,对数据库的表结构进行增删改的变化
升级需要的必要条件:
1.版本号的控制,前后的版本号肯定不能一致,不能有降级的操作
2.升级数据库的操作会调用onUpGrade()方法,因为在更新数据库的操作之前首先会默认删除所有的表,在重新创建
onUpGrade()的调用流程:
1.首先我们所有的数据库的管理操作和创建类操作都是在DaoMaster.DevOpenHelper中进行的,从源码中可以看到他是继承自OpenHelper

然后DevOpenHelper可以看出他是一个静态的内部类是继承的OpenHelper的,它里面有一个方法是onUpgrade(),他里面是对数据库进行的更新操作也就是说他在更新之前需要先删除所有的数据库操作,然后会去重新再创建,所以说他在每次删完库之后就会重新去创建。
在继续看OpenHelper()里面,他是继承的DatabaseOpenHelper的,也就是说他的构造函数都是继承与父类的实现

在onCreate里面进行了表的操作,再看OpenHelper他是一个静态的抽象的内部类的方法,但是没有在下面看到抽象方法,所以就看下他的父类DatabaseOpenHelper

可以看出他最终是继承了一个SQLiteOpenHelper的方法,也就是说OpenHelper最终还是继承了SQLiteOpenHelper

在最下面有一个前面所看到过的onUpgrade()方法,也就是说他最后在自己的基础上重写了一个
数据库升级:
1.在build.gradle的根目录和Model目录中进行配置
①:根目录:mavenCentral()// 添加的代码----根,
classpath'org.greenrobot:greendao-gradle-plugin:3.2.2' // add plugin

②:字目录中进行的配置:
在最顶部的applyplugin:'org.greenrobot.greendao' // apply plugin
在buildType下写初始化GreenDao配置-------需改daoPackage--的内容
greendao{
schemaVersion 1 //数据库版本号
daoPackage 'com.example.lenovo.demo.dao' //数据库全路径
targetGenDir 'src/main/java' //存放 位置
}
在dependencies下添加依赖://greendao
implementation'org.greenrobot:greendao:3.2.2' // add library
2.创建相应的表结构

3.然后点击Build进行生成相应的DaoMaster,DaoSession,UserDao三个相应的文件

4.然后进行相应的数据库的增删改查操作,最后进行数据库的操作就是改数据库的版本号,只能比原有的基础上加,不能去减少

DevOpenHelper,,DaoMaster在升级数据库的时候会把所有的表删除,然后会创建新的表,这样会造成原始数据的缺失,而且又应为OpenHelper中的SQLiteOpenHelpe的封装r是抽象的所以自行去配置
1.每次对表进行添加和删除修改的时候在DbUtility中引用自定义的那个类,应为自定义的那个类继承了DaoMaster.OpenHelper
2.在自定义的那个类里面继承DaoMaster.OpenHelper,然后重写他的两个方法

3.在onUpgrade中添加一行代码为
MigrationHelper.getInstance().migrate(db,TestDataDao.class);就ok拉
最后在app.builder中吧版本号修改为比原有的增加,版本号只能增加不能减少

数据库的更新就是为了性能最大化,对Android进行了高度优化
自定义的那个类直接占就行,不需要修改
public final class MigrationHelper {
public static boolean DEBUG = false;
private static String TAG = "MigrationHelper";
private static final String SQLITE_MASTER = "sqlite_master";
private static final String SQLITE_TEMP_MASTER = "sqlite_temp_master";
private static WeakReference<ReCreateAllTableListener> weakListener;
public interface ReCreateAllTableListener{
void onCreateAllTables(Database db, boolean ifNotExists);
void onDropAllTables(Database db, boolean ifExists);
}
public static void migrate(SQLiteDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
printLog("【The Old Database Version】" + db.getVersion());
Database database = new StandardDatabase(db);
migrate(database, daoClasses);
}
public static void migrate(SQLiteDatabase db, ReCreateAllTableListener listener, Class<? extends AbstractDao<?, ?>>... daoClasses) {
weakListener = new WeakReference<>(listener);
migrate(db, daoClasses);
}
public static void migrate(Database database, ReCreateAllTableListener listener, Class<? extends AbstractDao<?, ?>>... daoClasses) {
weakListener = new WeakReference<>(listener);
migrate(database, daoClasses);
}
public static void migrate(Database database, Class<? extends AbstractDao<?, ?>>... daoClasses) {
printLog("【Generate temp table】start");
generateTempTables(database, daoClasses);
printLog("【Generate temp table】complete");
ReCreateAllTableListener listener = null;
if (weakListener != null) {
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<? extends AbstractDao<?, ?>>... 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("【MyOpenHelper 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();
}
private static void dropAllTables(Database db, boolean ifExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
reflectMethod(db, "dropTable", ifExists, daoClasses);
printLog("【Drop all table by reflect】");
}
private static void createAllTables(Database db, boolean ifNotExists, @NonNull Class<? extends AbstractDao<?, ?>>... 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, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
if (daoClasses.length < 1) {
return;
}
try {
for (Class cls : daoClasses) {
Method method = cls.getDeclaredMethod(methodName, Database.class, boolean.class);
method.invoke(null, db, isExists);
}
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
private static 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");
if (!isTableExists(db, true, tempTableName)) {
continue;
}
try {
// get all columns from tempTable, take careful to use the columns list
List<TableInfo> newTableInfos = TableInfo.getTableInfo(db, tableName);
List<TableInfo> tempTableInfos = TableInfo.getTableInfo(db, tempTableName);
ArrayList<String> selectColumns = new ArrayList<>(newTableInfos.size());
ArrayList<String> intoColumns = new ArrayList<>(newTableInfos.size());
for (TableInfo tableInfo : tempTableInfos) {
if (newTableInfos.contains(tableInfo)) {
String column = '`' + tableInfo.name + '`';
intoColumns.add(column);
selectColumns.add(column);
}
}
// NOT NULL columns list
for (TableInfo tableInfo : newTableInfos) {
if (tableInfo.notnull && !tempTableInfos.contains(tableInfo)) {
String column = '`' + tableInfo.name + '`';
intoColumns.add(column);
String value;
if (tableInfo.dfltValue != null) {
value = "'" + tableInfo.dfltValue + "' AS ";
} else {
value = "'' AS ";
}
selectColumns.add(value + column);
}
}
if (intoColumns.size() != 0) {
StringBuilder insertTableStringBuilder = new StringBuilder();
insertTableStringBuilder.append("REPLACE INTO ").append(tableName).append(" (");
insertTableStringBuilder.append(TextUtils.join(",", intoColumns));
insertTableStringBuilder.append(") SELECT ");
insertTableStringBuilder.append(TextUtils.join(",", selectColumns));
insertTableStringBuilder.append(" FROM ").append(tempTableName).append(";");
db.execSQL(insertTableStringBuilder.toString());
printLog("【Restore data】 to " + tableName);
}
StringBuilder dropTableStringBuilder = new StringBuilder();
dropTableStringBuilder.append("DROP TABLE ").append(tempTableName);
db.execSQL(dropTableStringBuilder.toString());
printLog("【Drop temp table】" + tempTableName);
} catch (SQLException e) {
Log.e(TAG, "【Failed to restore data from temp table 】" + tempTableName, e);
}
}
}
private static List<String> getColumns(Database db, String tableName) {
List<String> columns = null;
Cursor cursor = null;
try {
cursor = db.rawQuery("SELECT * FROM " + tableName + " limit 0", null);
if (null != cursor && cursor.getColumnCount() > 0) {
columns = Arrays.asList(cursor.getColumnNames());
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (cursor != null)
cursor.close();
if (null == columns)
columns = new ArrayList<>();
}
return columns;
}
private static void printLog(String info){
if(DEBUG){
Log.d(TAG, info);
}
}
private static class TableInfo {
int cid;
String name;
String type;
boolean notnull;
String dfltValue;
boolean pk;
@Override
public boolean equals(Object o) {
return this == o
|| o != null
&& getClass() == o.getClass()
&& name.equals(((TableInfo) o).name);
}
@Override
public String toString() {
return "TableInfo{" +
"cid=" + cid +
", name='" + name + '\'' +
", type='" + type + '\'' +
", notnull=" + notnull +
", dfltValue='" + dfltValue + '\'' +
", pk=" + pk +
'}';
}
private static List<TableInfo> getTableInfo(Database db, String tableName) {
String sql = "PRAGMA table_info(" + tableName + ")";
printLog(sql);
Cursor cursor = db.rawQuery(sql, null);
if (cursor == null)
return new ArrayList<>();
TableInfo tableInfo;
List<TableInfo> tableInfos = new ArrayList<>();
while (cursor.moveToNext()) {
tableInfo = new TableInfo();
tableInfo.cid = cursor.getInt(0);
tableInfo.name = cursor.getString(1);
tableInfo.type = cursor.getString(2);
tableInfo.notnull = cursor.getInt(3) == 1;
tableInfo.dfltValue = cursor.getString(4);
tableInfo.pk = cursor.getInt(5) == 1;
tableInfos.add(tableInfo);
// printLog(tableName + ":" + tableInfo);
}
cursor.close();
return tableInfos;
}
}
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