【安卓筆記】ormlite入門
ps:寫這篇文章的目的是嘗試下新的markdown編輯器哈哈
簡單介紹
ORMLite provides a lightweight Object Relational Mapping between Java classes and SQL databases. There are certainly more mature ORMs which provide this functionality including Hibernate and iBatis. However, the author wanted a simple yet powerful wrapper around the JDBC functions, and Hibernate and iBatis are significantly more complicated with many dependencies.
Ormlite和GreenDao都是android平臺經常使用的orm框架。兩者各有優勢,ormlite勝在簡單,可是其基於註解反射。速度比不上greendao。
ormlite官網:http://ormlite.com/
註:ormlite不僅能夠用於android平臺,也能夠結合jdbc使用的
怎樣使用
- 首先你須要加入ormlite庫的依賴到build.gradle中:
dependencies {
compile ‘com.j256.ormlite:ormlite-core:4.48’
compile ‘com.j256.ormlite:ormlite-android:4.48’
}
- 創建一個bean映射數據庫中相應的table
比方我這裏想創建一個手機黑名單數據表,表名叫black,表相應字段例如以下:
id | name | number |
---|---|---|
主鍵、自增長 | 名稱 | 號碼 |
假設使用SqliteOpenHelper的話,須要在onCreate中運行sql語句創建table。可是使用ormlite只須要創建以下這個bean。
import com.j256.ormlite.field.DatabaseField;
import com.j256.ormlite.table.DatabaseTable;
/**
* Created by Rowandjj on 2015/5/26.
*/
@DatabaseTable(tableName = "black")
public class BlackEntity//映射到數據庫就是一個名為black的表
{
@DatabaseField(generatedId = true)
public int id;//使用DatabaseField註解表明這是一個字段
@DatabaseField
public String name;
@DatabaseField
public String number;
public BlackEntity(){}
public BlackEntity(String name, String number)
{
this.name = name;
this.number = number;
}
@Override
public String toString()
{
return "BlackEntity{" +
"id=" + id +
", name=‘" + name + ‘\‘‘ +
", number=‘" + number + ‘\‘‘ +
‘}‘;
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
public String getNumber()
{
return number;
}
public void setNumber(String number)
{
this.number = number;
}
}
很多其它註解如外鍵等等參見文檔
- 繼承OrmliteSqliteOpenHelper。並復寫相關方法
最基本的是onCreate和onUpgrade方法。
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import com.j256.ormlite.android.apptools.OrmLiteSqliteOpenHelper;
import com.j256.ormlite.dao.Dao;
import com.j256.ormlite.dao.RuntimeExceptionDao;
import com.j256.ormlite.support.ConnectionSource;
import com.j256.ormlite.table.TableUtils;
import com.taobao.easysafe.constants.DBConfig;
import java.sql.SQLException;
/**
* Created by Rowandjj on 2015/5/26.
*/
public class ListDBHelper extends OrmLiteSqliteOpenHelper
{
/**黑名單*/
private Dao<BlackEntity, Integer> mBlackDao;
private RuntimeExceptionDao<BlackEntity, Integer> mRuntimeBlackDao;
public ListDBHelper(Context context)
{
super(context, DBConfig.BW_LIST/*數據庫名稱*/, null, 1);
}
@Override
public void onCreate(SQLiteDatabase database, ConnectionSource connectionSource)
{
try
{
TableUtils.createTable(connectionSource, BlackEntity.class);
} catch (SQLException e)
{
e.printStackTrace();
}
}
@Override
public void onUpgrade(SQLiteDatabase database, ConnectionSource connectionSource, int oldVersion, int newVersion)
{
try
{
TableUtils.dropTable(connectionSource,BlackEntity.class);
onCreate(database, connectionSource);
}catch(Exception e)
{
e.printStackTrace();
}
}
public Dao<BlackEntity, Integer> getBlackDao() throws SQLException
{
if (mBlackDao == null)
{
mBlackDao = getDao(BlackEntity.class);
}
return mBlackDao;
}
public RuntimeExceptionDao<BlackEntity, Integer> getRuntimeExceptionBlackDao()
{
if(mRuntimeBlackDao == null)
{
mRuntimeBlackDao = getRuntimeExceptionDao(BlackEntity.class);
}
return mRuntimeBlackDao;
}
}
ormlite提供了TableUtils類幫我們運行創建/銷毀表的功能。
- 運行CRUD操作
要想運行CRUD操作,得首先拿到Dao,即調用ListDBHelper的getBlackDao或getRuntimeExceptionBlackDao方法,這兩個方法的差別是getRuntimeExceptionBlackDao不須要你寫一堆try catch,當出現故障時它會自己主動拋出異常。
如今問題來了,怎樣得到ListDBHelper實例呢?直接new嗎??當然不!數據庫連接是稀有資源,不應該創建多個實例。
Ormlite提供了OpenHelperManager類幫我們創建實例,調用靜態的getHelper就可以:
ListDBHelper mDBHelper;
private ListDBHelper getHelper()
{
if (mDBHelper == null)
{
mDBHelper = OpenHelperManager.getHelper(this/*Context實例*/, ListDBHelper.class);
}
return mDBHelper;
}
ListDBHelper使用完記得釋放,最佳實踐是放到Activity的onDestroy中:
@Override
protected void onDestroy()
{
super.onDestroy();
if (mDBHelper != null)
{
OpenHelperManager.releaseHelper();
mDBHelper = null;
}
}
有了mDBHelper實例後,我們就能夠拿到DAO。並調用其CRUD方法:
增:
private void addToBlack(ContactInfo info)
{
if (info != null && info.getName() != null && info.getNumber() != null)
{
BlackEntity entity = new BlackEntity(info.getName(), info.getNumber());
getHelper().getRuntimeExceptionBlackDao().create(entity);
}
}
查:
private List<BlackEntity> queryBlack()
{
return getHelper().getRuntimeExceptionBlackDao().queryForAll();
}
刪:
dao提供了一系列的delete方法。可參考文檔使用,這裏介紹一種更強大的DeleteBuilder,它能夠添加where條件,並且api是builder模式,不停的點點點,全然停不下來~haha,當然嘍,不不過DeleteBuilder,還有QueryBuilder、UpdateBuilder等
private void removeBlack(ContactInfo info)
{
int result = -1;
if(info != null)
{
Logger.d("TAG", info.getName() + "," + info.getNumber());
try
{
DeleteBuilder builder = getHelper().getRuntimeExceptionBlackDao().deleteBuilder();
builder.where().eq("name",info.getName()).and().eq("number",info.getNumber());
result = builder.delete();
} catch (SQLException e)
{
e.printStackTrace();
}
}
}
是不是非常easy?那就趕緊用起來吧!
ps:markdown的代碼高亮好難看
【安卓筆記】ormlite入門