Android开源：数据库ORM框架GreenDao学习心得及使用总结

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最近在对开发项目的性能进行优化。由于项目里涉及了大量的缓存处理和数据库运用，需要对数据库进行频繁的读写、查询等操作。因此首先想到了对整个项目的数据库框架进行优化。

原先使用android本身内置的sqllite，也就是用的最基本的SQLiteOpenHelper方法，这种方法对自己来说比较方便易懂。但是在使用过程中感觉很繁琐，从建表到对表的增删改查等操作，如果表对象的属性很多，就需要使用大量的代码来执行建表、插入等。在代码执行中还需要对数据库和游标的进行及时关闭(开启使用，用完关闭)，而且还需要部分sql语言，这在开发中产生bug进行调试时尤其不方便。

目前android经常用的orm框架主要有greenDAO、OrmLite、AndrORM。综合了网上的各种评价，greenDAO的运行效率最高，内存消耗最少，性能最佳。因此决定采用greenDAO框架，对项目的orm框架进行改进。

greenDAO与ORMLite性能对比

经过两天的修改，终于将项目里的数据库相关的都优化完了。在这过程中，发现greenDAO的性能确实不错，而且使用相当方便，不再需要涉及到任何的sql语言，可以直接通过对象类进行建表、增删改查等，尤其是api接口又方便易懂。在摸索学习中发现国内相关学习资料实在实在是太少，遂决定在此记录下自己对使用这个orm框架的一些心得和方法总结。

一、greenDAO相关

1.greenDAO官网：http://greendao-orm.com/

2.项目下载地址：https://github.com/greenrobot/greenDAO（或者官网）

greenDAO是一个可以帮助Android开发者快速将Java对象映射到SQLite数据库的表单中的ORM解决方案，通过使用一个简单的面向对象API，开发者可以对Java对象进行存储、更新、删除和查询。

greenDAO的主要设计目标：

*最大性能（最快的Android ORM）

*易于使用API

*高度优化

*最小内存消耗

二、使用步骤

官方Demo里共有六个工程目录，分别为：

(1).DaoCore：库目录，即jar文件greendao-1.3.0-beta-1.jar的代码；

(2).DaoExample：android范例工程；

(3).DaoExampleGenerator：DaoExample工程的DAO类构造器，java工程；

(4).DaoGenerator：DAO类构造器，java工程；

(5).DaoTest、PerformanceTestOrmLite：其他测试相关的工程。

（一）DAO类构造

首先需要新建一个java工程来生成DAO类文件，该工程需要导入greendao-generator.jar和freemarker.jar文件到项目中。

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package de.greenrobot.daogenerator.gentest;
import de.greenrobot.daogenerator.DaoGenerator;
import de.greenrobot.daogenerator.Entity;
import de.greenrobot.daogenerator.Property;
import de.greenrobot.daogenerator.Schema;
import de.greenrobot.daogenerator.ToMany;
/**
 * Generates entities and DAOs for the example project DaoExample.
 *
 * Run it as a Java application (not Android).
 *
 * @author Markus
 */
public class ExampleDaoGenerator
{
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
    public static void main(String[] args) throws Exception
    {
        Schema schema = new Schema(3, "de.greenrobot.daoexample");
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
        addNote(schema);
        addCustomerOrder(schema);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
        new DaoGenerator().generateAll(schema, "../DaoExample/src-gen");
    }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
    private static void addNote(Schema schema)
    {
        Entity note = schema.addEntity("Note");
        note.addIdProperty();
        note.addStringProperty("text").notNull();
        note.addStringProperty("comment");
        note.addDateProperty("date");
    }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
    private static void addCustomerOrder(Schema schema)
    {
        Entity customer = schema.addEntity("Customer");
        customer.addIdProperty();
        customer.addStringProperty("name").notNull();
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
        Entity order = schema.addEntity("Order");
        order.setTableName("ORDERS"); // "ORDER" is a reserved keyword
        order.addIdProperty();
        Property orderDate = order.addDateProperty("date").getProperty();
        Property customerId = order.addLongProperty("customerId").notNull().getProperty();
        order.addToOne(customer, customerId);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
        ToMany customerToOrders = customer.addToMany(order, customerId);
        customerToOrders.setName("orders");
        customerToOrders.orderAsc(orderDate);
    }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
}

在main方法中，

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Schema schema = new Schema(3, "de.greenrobot.daoexample");

该方法第一个参数用来更新数据库版本号，第二个参数为要生成的DAO类所在包路径。

然后进行建表和设置要生成DAO文件的目标工程的项目路径。

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addNote(schema);
addCustomerOrder(schema);
new DaoGenerator().generateAll(schema, "../DaoExample/src-gen");

其中src-gen这个目录名需要在运行前手动创建，否则会报错。

如果运行后出现以下错误，则导入DaoGenerator项目的dao.ftl文件即可(或者直接使用DaoGenerator来生成DAO文件)。

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Exception in thread "main" java.io.FileNotFoundException: Template "dao.ftl" not found.
    at freemarker.template.Configuration.getTemplate(Configuration.java:742)
    at freemarker.template.Configuration.getTemplate(Configuration.java:665)
    at de.greenrobot.daogenerator.DaoGenerator.<init>(DaoGenerator.java:68)
    at de.greenrobot.daogenerator.gentest.ExampleDaoGenerator.main(ExampleDaoGenerator.java:41)

运行后出现以下的提示说明DAO文件自动生成成功了，刷新一下DaoExample项目即可看到。

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greenDAO Generator
Copyright 2011-2013 Markus Junginger, greenrobot.de. Licensed under GPL V3.
This program comes with ABSOLUTELY NO WARRANTY
Processing schema version 3...
Written F:\Android_Ex\work_10\DaoExample\src-gen\de\greenrobot\daoexample\NoteDao.java
Written F:\Android_Ex\work_10\DaoExample\src-gen\de\greenrobot\daoexample\Note.java
Written F:\Android_Ex\work_10\DaoExample\src-gen\de\greenrobot\daoexample\CustomerDao.java
Written F:\Android_Ex\work_10\DaoExample\src-gen\de\greenrobot\daoexample\Customer.java
Written F:\Android_Ex\work_10\DaoExample\src-gen\de\greenrobot\daoexample\OrderDao.java
Written F:\Android_Ex\work_10\DaoExample\src-gen\de\greenrobot\daoexample\Order.java
Written F:\Android_Ex\work_10\DaoExample\src-gen\de\greenrobot\daoexample\DaoMaster.java
Written F:\Android_Ex\work_10\DaoExample\src-gen\de\greenrobot\daoexample\DaoSession.java
Processed 3 entities in 204ms

运行后可以看到，DaoExample项目src-gen下面自动生成了8个文件，3个实体对象，3个dao，1个DaoMaster,1个DaoSession.

(二)创建表

1.创建一个实体类

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Entity note = schema.addEntity("Note");

默认表名就是类名，也可以自定义表名

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dao.setTableName("NoteList");

greenDAO会自动根据实体类属性创建表字段，并赋予默认值。例如在数据库方面的表名和列名都来源于实体类名和属性名。默认的数据库名称是大写使用下划线分隔单词，而不是在Java中使用的驼峰式大小写风格。例如，一个名为“CREATIONDATE”属性将成为一个数据库列“CREATION_DATE”。

设置一个自增长ID列为主键：

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dao.addIdProperty().primaryKey().autoincrement();

设置其他各种类型的属性：

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dao.addIntProperty("cityId");
dao.addStringProperty("infoType").notNull();//非null字段
dao.addDoubleProperty("Id");

在生成的实体类中,int类型为自动转为long类型。

如果在编译过程中出现以下错误，那么有可能是主键的类型错误所致：

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java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String

在使用greenDAO时，一个实体类只能对应一个表，目前没法做到一个表对应多个实体类，或者多个表共用一种对象类型。后续的升级也不会针对这一点进行扩展。

(二)表的增删改查

增删改查相当方便，完全的面向对象，不需要涉及到任何的sql语言。

1.查询

范例1：查询某个表是否包含某个id:

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public boolean isSaved(int ID)
{
    QueryBuilder<SaveList> qb = saveListDao.queryBuilder();
    qb.where(Properties.Id.eq(ID));
    qb.buildCount().count();
    return qb.buildCount().count() > 0 ? true : false;
}

范例2：获取整个表的数据集合,一句代码就搞定！

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public List<PhotoGalleryDB> getPhotoGallery()
{
    return photoGalleryDao.loadAll();// 获取图片相册
}

范例3：通过一个字段值查找对应的另一个字段值(为简便直接使用下面方法，也许有更简单的方法，尚未尝试)

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/** 通过图片id查找其目录id */
public int getTypeId(int picId)
{
    QueryBuilder<PhotoGalleryDB> qb = photoGalleryDao.queryBuilder();
    qb.where(Properties.Id.eq(picId));
    if (qb.list().size() > 0)
    {
        return qb.list().get(0).getTypeId();
    }
    else
    {
        return -1;
    }
}

范例4：查找所有第一姓名是“Joe”并且以lastname排序。

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List joes = userDao.queryBuilder()
.where(Properties.FirstName.eq("Joe"))
.orderAsc(Properties.LastName)
.list();

范例5：多重条件查询

(1)获取id为cityId并且infotype为HBContant.CITYINFO_SL的数据集合：

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public List<CityInfoDB> getSupportingList(int cityId)
{
    QueryBuilder<CityInfoDB> qb = cityInfoDao.queryBuilder();
    qb.where(qb.and(Properties.CityId.eq(cityId),Properties.InfoType.eq(HBContant.CITYINFO_SL)));
    qb.orderAsc(Properties.Id);// 排序依据
    return qb.list();
}

(2)获取firstname为“Joe”并且出生于1970年10月以后的所有user集合:

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QueryBuilder qb = userDao.queryBuilder();
qb.where(Properties.FirstName.eq("Joe"),
qb.or(Properties.YearOfBirth.gt(1970),
qb.and(Properties.YearOfBirth.eq(1970), Properties.MonthOfBirth.ge(10))));
List youngJoes = qb.list();

范例6：获取某列对象

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picJsonDao.loadByRowId(picId);

2.增添/插入、修改

插入数据更加简单，也是只要一句代码便能搞定!

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public void addToPhotoTable(Photo p)
{
    photoDao.insert(p);
}

插入时需要new一个新的对象，范例如下:

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DevOpenHelper helper = new DaoMaster.DevOpenHelper(this, "notes-db", null);
 db = helper.getWritableDatabase();
 daoMaster = new DaoMaster(db);
 daoSession = daoMaster.newSession();
 noteDao = daoSession.getNoteDao();
 Note note = new Note(null, noteText, comment, new Date());
 noteDao.insert(note);

修改更新：

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photoDao.insertOrReplace(photo);
photoDao.insertInTx(photo);

3.删除:

(1)清空表格数据

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/** 清空相册图片列表的数据 */
public void clearPhoto()
{
    photoDao.deleteAll();
}

(2)删除某个对象

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public void deleteCityInfo(int cityId)
{
    QueryBuilder<DBCityInfo> qb = cityInfoDao.queryBuilder();
    DeleteQuery<DBCityInfo> bd = qb.where(Properties.CityId.eq(cityId)).buildDelete();
    bd.executeDeleteWithoutDetachingEntities();
}

参考：https://github.com/greenrobot/greenDAO/issues/34

由上可见，使用greenDAO进行数据库的增删改查时及其方便，而且性能极佳。

(三)常用方法笔记

1.在Application实现得到DaoMaster和DaoSession的方法：

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private static DaoMaster daoMaster;
private static DaoSession daoSession;
/**
 * 取得DaoMaster
 *
 * @param context
 * @return
 */
public static DaoMaster getDaoMaster(Context context)
{
    if (daoMaster == null)
    {
        OpenHelper helper = new DaoMaster.DevOpenHelper(context, HBContant.DATABASE_NAME, null);
        daoMaster = new DaoMaster(helper.getWritableDatabase());
    }
    return daoMaster;
}
/**
 * 取得DaoSession
 *
 * @param context
 * @return
 */
public static DaoSession getDaoSession(Context context)
{
    if (daoSession == null)
    {
        if (daoMaster == null)
        {
            daoMaster = getDaoMaster(context);
        }
        daoSession = daoMaster.newSession();
    }
    return daoSession;
}

2.增删改查工具类:

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public class DBHelper
{
    private static Context mContext;
    private static DBHelper instance;
                                                                                                                                                                                                                                                                                                                                   
    private CityInfoDBDao cityInfoDao;
                                                                                                                                                                                                                                                                                                                                   
    private DBHelper()
    {
    }
                                                                                                                                                                                                                                                                                                                                   
    public static DBHelper getInstance(Context context)
    {
        if (instance == null)
        {
            instance = new DBHelper();
            if (mContext == null)
            {
                mContext = context;
            }
                                                                                                                                                                                                                                                                                                                                           
            // 数据库对象
            DaoSession daoSession = HBApplication.getDaoSession(mContext);
            instance.cityInfoDao = daoSession.getCityInfoDBDao();
        }
        return instance;
    }
                                                                                                                                                                                                                                                                                                                                   
    /** 添加数据 */
    public void addToCityInfoTable(CityInfo item)
    {
        cityInfoDao.insert(item);
    }
                                                                                                                                                                                                                                                                                                                                   
    /** 查询 */
    public List<EstateLoveListJson> getCityInfoList()
    {
        QueryBuilder<CityInfo> qb = cityInfoDao.queryBuilder();
        return qb.list();
    }
                                                                                                                                                                                                                                                                                                                                   
    /** 查询 */
    public List<CityInfo> getCityInfo()
    {
        return cityInfoDao.loadAll();// 查找图片相册
    }
                                                                                                                                                                                                                                                                                                                                   
    /** 查询 */
    public boolean isSaved(int Id)
    {
        QueryBuilder<CityInfo> qb = cityInfoDao.queryBuilder();
        qb.where(Properties.Id.eq(Id));
        qb.buildCount().count();
        return qb.buildCount().count() > 0 ? true : false;// 查找收藏表
    }
                                                                                                                                                                                                                                                                                                                                   
    /** 删除 */
    public void deleteCityInfoList(int Id)
    {
        QueryBuilder<CityInfo> qb = cityInfoDao.queryBuilder();
        DeleteQuery<CityInfo> bd = qb.where(Properties.Id.eq(Id)).buildDelete();
        bd.executeDeleteWithoutDetachingEntities();
    }
                                                                                                                                                                                                                                                                                                                                   
    /** 删除 */
    public void clearCityInfo()
    {
        cityInfoDao.deleteAll();
    }
                                                                                                                                                                                                                                                                                                                                   
    /** 通过城市id查找其类型id */
    public int getTypeId(int cityId)
    {
        QueryBuilder<CityInfo> qb = cityInfoDao.queryBuilder();
        qb.where(Properties.Id.eq(cityId));
        if (qb.list().size() > 0)
        {
            return qb.list().get(0).getTypeId();
        }
        else
        {
            return 0;
        }
    }
                                                                                                                                                                                                                                                                                                                                   
    /** 多重查询 */
    public List<CityInfo> getIphRegionList(int cityId)
    {
        QueryBuilder<CityInfoDB> qb = cityInfoDao.queryBuilder();
        qb.where(qb.and(Properties.CityId.eq(cityId), Properties.InfoType.eq(HBContant.CITYINFO_IR)));
        qb.orderAsc(Properties.Id);// 排序依据
        return qb.list();
    }
}

另外，还有多表关联、惰性加载等功能，待后续研究。

参考资料：

1.https://github.com/greenrobot/greenDAO

2.http://greendao-orm.com/documentation/how-to-get-started/

3.http://blog.csdn.net/krislight/article/details/9391455

4.http://blog.loadlimits.info/2013/01/androidのorm、greendaoを使ってみた/

5.http://leebart.tumblr.com/post/58408230144/how-to-daogenerator

6.http://www.androidanalyse.com/greendao-an-android-orm-for-sqlite/

本文转载于:http://glblong.blog.51cto.com/3058613/1354953

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