OrmLite动态创建表，一个实体类创建多张表的的偏招

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/LonelyRoamer/article/details/26299355

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);
			}
		}

2、ChatMessageDaoImpl指定daoClass

@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*/
}

3、仿照DaoManager，实现一个不缓存的UnlimitDaoManager

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;
	}

}

4、因为上面没有使用DaoManager，所以为了性能和安全的考虑，我们还是要基本的实现以下缓存功能，下一个数据库操作的工具类，如下：

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。