专注于Android开发，分享经验总结，欢迎加入
在项目中用到了数据库存储，于是选择了greendao，但是在增删字段时数据库中的表都会重新去创建一次，原有的数据都会删除，所以就需要对数据库做处理，在这期间查了好多资料，确实学到了好多，特此记录
1.数据库每次升级都会走onUpgrade（）方法，在此回调中做操作
/**
* 数据库升级策略
* Email:yin13753884368@163.com
* CSDN:http://blog.csdn.net/yin13753884368/article
* Github:https://github.com/taxiao213
*/
public class DBOpenHelper extends DatabaseOpenHelper {
public DBOpenHelper(Context context, String name) {
super(context, name, SCHEMA_VERSION);
}
@Override
public void onCreate(Database db) {
super.onCreate(db);
DaoMaster.createAllTables(db, false);
}
@Override
public void onUpgrade(final Database db, int oldVersion, int newVersion) {
switch (oldVersion) {
case 1://方法预留 哪个表增删字段，传入那个类
Executors.newSingleThreadExecutor().execute(new Runnable() {
@Override
public void run() {
LogUtils.e("DBOpenHelper --- onUpgrade");
// DBMigrationHelper.getInstance().migrate(db, MsgTipInfoDao.class);
}
});
}
}
}
2.可以看到每次在升级时都会走onUpgrade()方法，每次都会把表先移除掉，再去创建，所以很多信息数据是无法保留的，所以我们要去自己实现，
步骤：备份 --> 删除需要更新的表 --> 创建需要更新的表 --> 恢复数据
/**
* 数据迁移的策略
* Email:yin13753884368@163.com
* CSDN:http://blog.csdn.net/yin13753884368/article
* Github:https://github.com/taxiao213
*/
public class DBMigrationHelper {
private static final String CONVERSION_CLASS_NOT_FOUND_EXCEPTION =
"MIGRATION HELPER - CLASS DOESN'T MATCH WITH THE CURRENT PARAMETERS";
private static DBMigrationHelper migrationHelper;
private DBMigrationHelper() {
}
public static DBMigrationHelper getInstance() {
if (migrationHelper == null) {
synchronized (DBMigrationHelper.class) {
if (migrationHelper == null) {
migrationHelper = new DBMigrationHelper();
}
}
}
return migrationHelper;
}
public void migrate(Database db, Class<? extends AbstractDao<?, ?>> daoClasses) {
//1. 备份
generateTempTables(db, daoClasses);
//2. 只删除需要更新的表 DaoMaster.dropAllTables(db, true);
deleteTables(db, daoClasses);
//3. 只创建需要更新的表 DaoMaster.createAllTables(db, false);
createTables(db, daoClasses);
//4. 恢复数据
restoreData(db, daoClasses);
}
/**
* 恢复数据
*
* @param db
* @param daoClasses
*/
private void restoreData(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
String primarykey = null;//约束键 insert 时不能select
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();
ArrayList<DBTableColumn> list = new ArrayList<>();//表中多出的参数
for (int j = 0; j < daoConfig.properties.length; j++) {
String columnName = daoConfig.properties[j].columnName;
if (getColumns(db, tempTableName).contains(columnName)) {
columnName = resultColumnName(columnName);
properties.add(columnName);
if (daoConfig.properties[j].primaryKey) {
primarykey = columnName;
}
} else {
//表中多出的参数
String type = null;
try {
type = getTypeByClass(daoConfig.properties[j].type);
list.add(new DBTableColumn(columnName, type));
} catch (Exception exception) {
}
}
}
if (properties != null && properties.size() > 0) {
Iterator<String> iterator = properties.iterator();
while (iterator.hasNext()) {
String next = iterator.next();
if (TextUtils.equals(primarykey, next)) {
//(2018.08.06) UNIQUE constraint failed: MSG_TIP_DO_INFO._id 所以删掉_id
iterator.remove();
}
}
}
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);
try {
db.execSQL(insertTableStringBuilder.toString());
db.execSQL(dropTableStringBuilder.toString());
if (list != null && list.size() > 0) {
ArrayList<String> arrayList = new ArrayList<>();
for (int j = 0; j < list.size(); j++) {
DBTableColumn tableColumn = list.get(j);
if (TextUtils.equals(tableColumn.getTypes(), "INTEGER") || TextUtils.equals(tableColumn.getTypes(), "BOOLEAN")) {
arrayList.add(tableColumn.getColumnName());
}
}
if (arrayList != null && arrayList.size() > 0) {
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append("UPDATE ").append(tableName).append(" SET");
for (int j = 0; j < arrayList.size(); j++) {
String name = arrayList.get(j);
stringBuilder.append(" ");
stringBuilder.append(name);
stringBuilder.append(" = ");
stringBuilder.append(0);
if (j == arrayList.size() - 1) {
stringBuilder.append(";");
} else {
stringBuilder.append(",");
}
}
db.execSQL(stringBuilder.toString());
LogUtils.e("DBOpenHelper ---", "更新语句 stringBuilder ===" + stringBuilder.toString());
if (arrayList.contains("IS_READ_MESSAGE")) {
StringBuilder st = new StringBuilder();
st.append("UPDATE ").append(tableName).append(" SET IS_READ_MESSAGE = 1;");
db.execSQL(st.toString());
LogUtils.e("DBOpenHelper ---", "更新语句 st ===" + st.toString());
}
}
LogUtils.e("DBOpenHelper ---", "添加的参数 list.size =" + list.toString());
}
} catch (Exception e) {
LogUtils.e("DBOpenHelper ---", "错误" + e.getMessage() + " 添加的参数 list.size =" + list.toString());
}
}
LogUtils.e("DBOpenHelper----", "restoreData 恢复数据");
}
/**
* 创建表
*
* @param db
* @param daoClasses
*/
private void createTables(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
String buildType = BuildConfig.BUILD_TYPE;
if (TextUtils.equals(buildType, "debug")) {
for (Class<? extends AbstractDao<?, ?>> daoClass : daoClasses) {
try {
Method method = daoClass.getMethod("createTable", Database.class, boolean.class);
method.invoke(null, db, false);
} catch (Exception e) {
LogUtils.e("DBOpenHelper---- createTables debug e == " + e.getMessage());
e.printStackTrace();
}
}
} else {
for (int i = 0; i < daoClasses.length; i++) {
DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);
String tableName = daoConfig.tablename;
StringBuilder createTableStringBuilder = new StringBuilder();
createTableStringBuilder.append("CREATE TABLE ").append(tableName).append(" (");
String divider = "";
try {
for (int j = 0; j < daoConfig.properties.length; j++) {
String columnName = daoConfig.properties[j].columnName;
columnName = resultColumnName(columnName);
String type = null;
type = getTypeByClass(daoConfig.properties[j].type);
createTableStringBuilder.append(divider).append(columnName).append(" ").append(type);
if (daoConfig.properties[j].primaryKey) {
createTableStringBuilder.append(" PRIMARY KEY");
}
divider = ",";
}
createTableStringBuilder.append(");");
db.execSQL(createTableStringBuilder.toString());
LogUtils.e("DBOpenHelper ---createTables release sql== " + createTableStringBuilder.toString());
} catch (Exception e) {
LogUtils.e("DBOpenHelper ---createTables release e == " + e.getMessage());
}
}
}
}
/**
* 删除表
*
* @param db
* @param daoClasses
*/
private void deleteTables(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
String buildType = BuildConfig.BUILD_TYPE;
if (TextUtils.equals(buildType, "debug")) {
for (Class<? extends AbstractDao<?, ?>> daoClass : daoClasses) {
try {
Method method = daoClass.getMethod("dropTable", Database.class, boolean.class);
method.invoke(null, db, true);
} catch (Exception e) {
LogUtils.e("DBOpenHelper---- debug deleteTables e == " + e.getMessage());
e.printStackTrace();
}
}
} else {
for (int i = 0; i < daoClasses.length; i++) {
try {
DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);
StringBuilder dropTableStringBuilder = new StringBuilder();
String tableName = daoConfig.tablename;
dropTableStringBuilder.append("DROP TABLE ").append(tableName);
db.execSQL(dropTableStringBuilder.toString());
LogUtils.e("DBOpenHelper---- release deleteTables sql== " + dropTableStringBuilder.toString());
} catch (Exception e) {
LogUtils.e("DBOpenHelper---- release deleteTables e == " + e.getMessage());
}
}
}
}
/**
* 备份表
*
* @param db
* @param daoClasses
*/
private void generateTempTables(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
String primarykey = null;//约束键 insert 时不能select
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)) {
columnName = resultColumnName(columnName);
properties.add(columnName);
String type = null;
try {
type = getTypeByClass(daoConfig.properties[j].type);
} catch (Exception exception) {
}
createTableStringBuilder.append(divider).append(columnName).append(" ").append(type);
if (daoConfig.properties[j].primaryKey) {
primarykey = columnName;
createTableStringBuilder.append(" PRIMARY KEY");
}
divider = ",";
}
}
createTableStringBuilder.append(");");
try {
db.execSQL(createTableStringBuilder.toString());
LogUtils.e("DBOpenHelper ---", "generateTempTables create sql== " + createTableStringBuilder.toString());
} catch (Exception e) {
LogUtils.e("DBOpenHelper ---", "generateTempTables create e== " + e.getMessage());
}
if (properties != null && properties.size() > 0) {
Iterator<String> iterator = properties.iterator();
while (iterator.hasNext()) {
String next = iterator.next();
if (TextUtils.equals(primarykey, next)) {
iterator.remove();
}
}
}
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(";");
try {
db.execSQL(insertTableStringBuilder.toString());
LogUtils.e("DBOpenHelper ---", "generateTempTables insert sql== " + insertTableStringBuilder.toString());
} catch (Exception e) {
LogUtils.e("DBOpenHelper ---", "generateTempTables insert e== " + e.getMessage());
}
}
}
/**
* 获取列数
*
* @param db
* @param tableName
* @return
*/
private static 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) {
LogUtils.e("DBOpenHelper ---getColumns", e.getMessage());
e.printStackTrace();
} finally {
if (cursor != null)
cursor.close();
}
return columns;
}
private String getTypeByClass(Class<?> type) throws Exception {
if (type.equals(String.class)) {
return "TEXT";
}
if (type.equals(int.class) || type.equals(Long.class) || type.equals(Integer.class) || type.equals(long.class)) {
return "INTEGER";
}
if (type.equals(boolean.class) || type.equals(Boolean.class)) {
return "BOOLEAN";
}
Exception exception =
new Exception(CONVERSION_CLASS_NOT_FOUND_EXCEPTION.concat(" - Class: ").concat(type.toString()));
throw exception;
}
/**
* 关键字 替换
*
* @param columnName
*/
String[] arr = new String[]{"FROM", "TO", "TIME", "CONTENT", "NAME", "SELECT", "INSERT", "DELETE", "UPDATE", "ADD", "VISIBLE", "TYPE"};
List<String> list = Arrays.asList(arr);
private String resultColumnName(String columnName) {
if (list.contains(columnName)) {
columnName = "`" + columnName + "`";
}
return columnName;
}
}
