在做一个Android的项目，因为使用数据库频繁，实体字段也比较多，于是打算采用ORM框架，发现OrmLite还不错，于是下了下来，打算使用。
没想到还没正式开工，就遇到问题了。我现在的一个需求如下，
我有一个实体类如下，代表聊天消息，现在要做的是针对每一个当前用户（userId）对应一个朋友（friendId）都要创建一个表。需求比较蛋疼，我本来想的是直接在加两个字段就搞定的，但是我们老大说要分表。没办法只能分表。
public class ChatMessage{
public ChatMessage() {
}
private int _id;
private int type;
private String content;
/*get and set...*/
}
在OrmLite里面创建表和Dao的基本用法如下：
DatabaseTableConfig<ChatMessage> config = DatabaseTableConfigUtil.fromClass(mHelper.getConnectionSource(), ChatMessage.class); TableUtils.createTableIfNotExists(mHelper.getConnectionSource(),config); dao = DaoManager.createDao(mHelper.getConnectionSource(), config);
这样我们就拿到了Dao对象，就可以进行数据操作了。但是这个方法的对我上面的需求并不管用，因为此方法拿到的数据库表名是固定的tableName="ChatMessage"，我现在逍遥的表名肯定是不能固定的，他的格式是tableName="ChatMessage"+userId+friendId。即使在confi里面config.setTableName(tableName) 一样不管用。
查看了OrmLite的源码，发现在DaoManager里面，根据同样的DatabaseTableConfig和类名做了缓存，于是每次拿到的Dao都是同样的Dao
TableConfigConnectionSource tableKey = new TableConfigConnectionSource(connectionSource, tableConfig);
// look up in the table map
Dao<?, ?> dao = lookupDao(tableKey);
if (dao != null) {
@SuppressWarnings("unchecked")
D castDao = (D) dao;
return castDao;
}
// now look it up in the class map
Class<T> dataClass = tableConfig.getDataClass();
ClassConnectionSource classKey = new ClassConnectionSource(connectionSource, dataClass);
dao = lookupDao(classKey);
if (dao != null) {
// if it is not in the table map but is in the class map, add it
addDaoToTableMap(tableKey, dao);
@SuppressWarnings("unchecked")
D castDao = (D) dao;
return castDao;
}同样的TableUtils.createTableIfNotExists一样进行了判断，使得你的相同的实体类不能创建多张表。
OrmLite这样做肯定是为了性能的优化和数据异步操作的安全性，但是这却妨碍了更加方便的使用了。于是研究下，稍微使了点偏招，来达到我上面的需求。
1、首先建个类，如下：
import java.sql.SQLException;
import com.j256.ormlite.dao.BaseDaoImpl;
import com.j256.ormlite.support.ConnectionSource;
import com.j256.ormlite.table.DatabaseTableConfig;
import com.roamer.bean.ChatMessage;
public class ChatMessageDaoImpl extends BaseDaoImpl<ChatMessage, Integer>{
public ChatMessageDaoImpl(ConnectionSource connectionSource, DatabaseTableConfig<ChatMessage> tableConfig) throws SQLException {
super(connectionSource, tableConfig);
}
}
实现BaseDaoImpl的原因是，查看源码，发现在DaoManager.createDao中实例化普通Modal，最后实际都是BaseDaoImpl类。
DatabaseTable databaseTable = tableConfig.getDataClass().getAnnotation(DatabaseTable.class);
if (databaseTable == null || databaseTable.daoClass() == Void.class
|| databaseTable.daoClass() == BaseDaoImpl.class) {
Dao<T, ?> daoTmp = BaseDaoImpl.createDao(connectionSource, tableConfig);
dao = daoTmp;
} else {
Class<?> daoClass = databaseTable.daoClass();
Object[] arguments = new Object[] { connectionSource, tableConfig };
Constructor<?> constructor = findConstructor(daoClass, arguments);
if (constructor == null) {
throw new SQLException(
"Could not find public constructor with ConnectionSource, DatabaseTableConfig parameters in class "
+ daoClass);
}
try {
dao = (Dao<?, ?>) constructor.newInstance(arguments);
} catch (Exception e) {
throw SqlExceptionUtil.create("Could not call the constructor in class " + daoClass, e);
}
}
@DatabaseTable(daoClass=ChatMessageDaoImpl.class)
public class ChatMessage{
public ChatMessage() {
}
@DatabaseField(generatedId=true)
private int _id;
@DatabaseField
private int type;
@DatabaseField
private String content;
/*get and set*/
}
package com.roamer.db;
import java.lang.reflect.Constructor;
import java.sql.SQLException;
import com.j256.ormlite.dao.BaseDaoImpl;
import com.j256.ormlite.dao.Dao;
import com.j256.ormlite.misc.SqlExceptionUtil;
import com.j256.ormlite.support.ConnectionSource;
import com.j256.ormlite.table.DatabaseTable;
import com.j256.ormlite.table.DatabaseTableConfig;
public class UnlimitDaoManager {
public synchronized static <D extends Dao<T, ?>, T> D createDao(ConnectionSource connectionSource,
DatabaseTableConfig<T> tableConfig) throws SQLException {
if (connectionSource == null) {
throw new IllegalArgumentException("connectionSource argument cannot be null");
}
return doCreateDao(connectionSource, tableConfig);
}
private static Constructor<?> findConstructor(Class<?> daoClass, Object[] params) {
for (Constructor<?> constructor : daoClass.getConstructors()) {
Class<?>[] paramsTypes = constructor.getParameterTypes();
if (paramsTypes.length == params.length) {
boolean match = true;
for (int i = 0; i < paramsTypes.length; i++) {
if (!paramsTypes[i].isAssignableFrom(params[i].getClass())) {
match = false;
break;
}
}
if (match) {
return constructor;
}
}
}
return null;
}
private static <D extends Dao<T, ?>, T> D doCreateDao(ConnectionSource connectionSource,
DatabaseTableConfig<T> tableConfig) throws SQLException {
Dao<?, ?> dao = null;
// build the DAO using the table information
DatabaseTable databaseTable = tableConfig.getDataClass().getAnnotation(DatabaseTable.class);
if (databaseTable == null || databaseTable.daoClass() == Void.class
|| databaseTable.daoClass() == BaseDaoImpl.class) {
return null;
} else {
Class<?> daoClass = databaseTable.daoClass();
Object[] arguments = new Object[] { connectionSource, tableConfig };
Constructor<?> constructor = findConstructor(daoClass, arguments);
if (constructor == null) {
throw new SQLException(
"Could not find public constructor with ConnectionSource, DatabaseTableConfig parameters in class "
+ daoClass);
}
try {
dao = (Dao<?, ?>) constructor.newInstance(arguments);
} catch (Exception e) {
throw SqlExceptionUtil.create("Could not call the constructor in class " + daoClass, e);
}
}
@SuppressWarnings("unchecked")
D castDao = (D) dao;
return castDao;
}
}
package com.roamer.dao;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import android.content.Context;
import android.database.Cursor;
import android.util.Log;
import com.j256.ormlite.android.DatabaseTableConfigUtil;
import com.j256.ormlite.android.apptools.OpenHelperManager;
import com.j256.ormlite.dao.Dao;
import com.j256.ormlite.table.DatabaseTableConfig;
import com.roamer.bean.ChatMessage;
import com.roamer.db.SQLiteHelper;
import com.roamer.db.UnlimitDaoManager;
public class ChatMessageUtil {
private static ChatMessageUtil instance;
public static ChatMessageUtil getInstance(Context context) {
if (instance == null) {
instance = new ChatMessageUtil(context);
}
return instance;
}
private SQLiteHelper mHelper;
private static final String PREFIX = "message_prefix";
public ChatMessageUtil(Context context) {
mHelper = OpenHelperManager.getHelper(context, SQLiteHelper.class);
}
private Map<String, Dao<ChatMessage, Integer>> mDaoMap = new HashMap<String, Dao<ChatMessage, Integer>>();
private Dao<ChatMessage, Integer> getDao(String userId, String friendId) {
String tableName = PREFIX + userId + friendId;
if (mDaoMap.containsKey(tableName)) {
return mDaoMap.get(tableName);
}
Dao<ChatMessage, Integer> dao = null;
try {
DatabaseTableConfig<ChatMessage> config = DatabaseTableConfigUtil.fromClass(mHelper.getConnectionSource(), ChatMessage.class);
config.setTableName(tableName);
createTableIfNotExist(tableName);
dao = UnlimitDaoManager.createDao(mHelper.getConnectionSource(), config);
} catch (SQLException e) {
e.printStackTrace();
}
if (dao != null) {
mDaoMap.put(tableName, dao);
}
return dao;
}
private void createTableIfNotExist(String tableName) {
if (isTableExist(tableName)) {
return;
}
String sql = "CREATE TABLE " + tableName + " (content VARCHAR , _id INTEGER PRIMARY KEY AUTOINCREMENT , type INTEGER )";
mHelper.getWritableDatabase().execSQL(sql);
Log.d("roamer", "isTableExist(tableName):" + isTableExist(tableName));
}
private boolean isTableExist(String tableName) {
boolean result = false;
if (tableName == null) {
return false;
}
Cursor cursor = null;
try {
String sql = "select count(*) as c from Sqlite_master where type =‘table‘ and name =‘" + tableName.trim() + "‘ ";
cursor = mHelper.getReadableDatabase().rawQuery(sql, null);
if (cursor.moveToNext()) {
int count = cursor.getInt(0);
if (count > 0) {
result = true;
}
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (cursor != null) {
cursor.close();
}
}
return result;
}
public void addMessage(String userId, String friendId, ChatMessage message) {
Dao<ChatMessage, Integer> dao = getDao(userId, friendId);
try {
dao.create(message);
} catch (SQLException e) {
e.printStackTrace();
}
}
public List<ChatMessage> getAllMessage(String userId, String friendId) {
Dao<ChatMessage, Integer> dao = getDao(userId, friendId);
try {
return dao.queryForAll();
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
}
在这个里面，没有使用TableUtils来创建表，而是使用了原生SQL语句。
最后经测试，可以达到我拿蛋疼的需求。
写这个文章，是看到有人遇到和我相同的需求，不知道怎么解决，需求有点帮助。
OrmLite动态创建表，一个实体类创建多张表的的偏招,布布扣,bubuko.com
原文：http://blog.csdn.net/lonelyroamer/article/details/26299355