本文主要是介绍GreenDao 3.0 简介、使用及踩坑，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
一、GreenDao 简介
GreenDAO 是一款开源的面向 Android 的轻便、快捷的 ORM 框架，将 Java 对象映射到 SQLite 数据库中，我们操作数据库的时候，不再需要编写复杂的 SQL语句， 在性能方面，greenDAO 针对 Android 进行了高度优化，最小的内存开销 、依赖体积小 同时还是支持 数据库加密。
greenDAO 官网地址：greenrobot.org/greendao/
greenDAO GitHub 源码地址：greenrobot/greenDAO
二、GreenDao 特征
- 1、支持 protocol buffer(protobuf) 协议
GreenDao 支持 protocol buffer(protobuf) 协议数据的直接存储，如果你通过 protobuf 协议与服务器交互，将不需要任何的映射 - 2、代码生成
greenDAO 会根据配置信息自动生成核心管理类以及 DAO 对象 - 3、性能
所有 ORM 数据库的，greenDAO 是最快的，greenDAO 不作性能方面任何妥协
三、核心类介绍
1、DaoMaster：
使用 greenDAO 的入口点。DaoMaster 负责管理数据库对象(SQLiteDatabase)和 DAO 类(对象)，我们可以通过它内部类 OpenHelper 和 DevOpenHelper SQLiteOpenHelper 创建不同模式的 SQLite 数据库。
2、DaoSession :
管理指定模式下的所有 DAO 对象，DaoSession 提供了一些通用的持久性方法比如插入、负载、更新和删除实体。
3、XxxDAO :
对于每个实体类， greenDAO 都会生成一个与之对应 DAO 对象，如：User 实体，则会生成一个 UserDao 类
4、Entities：
可持久化对象。通常，实体对象代表一个数据库行，使用标准 Java 属性(如一个 POJO 或 JavaBean )
四、集成 GreenDao
a、设置仓库与插件（Project： build.gradle）
buildscript {repositories {jcenter()mavenCentral() // add repository}dependencies {classpath 'com.android.tools.build:gradle:3.1.3'classpath 'org.greenrobot:greendao-gradle-plugin:3.2.2' // add plugin}
}
b、配置依赖 ( Module：app build.gradle )
apply plugin: 'com.android.application'
apply plugin: 'org.greenrobot.greendao' // apply plugindependencies {compile 'org.greenrobot:greendao:3.2.2' // add library// This is only needed if you want to use encrypted databasescompile 'net.zetetic:android-database-sqlcipher:3.5.6' //加密库依赖（可选项）
}
c、配置数据库相关信息 ( Module：app build.gradle )
greendao {schemaVersion 1 // 数据库版本号daoPackage 'com.example.zhangruirui.greendao' // 设置 DaoMaster、DaoSession、Dao 包名targetGenDir 'src/main/java' // 设置 DaoMaster、DaoSession、Dao 目录
}
d、基本使用步骤
// 生成数据库文件，名为 students-db
DaoMaster.DevOpenHelper helper = new DaoMaster.DevOpenHelper(this, "students-db", null);
SQLiteDatabase db = helper.getWritableDatabase();
// 建立特定模式下的所有的 DAO 对象和数据 db 对象的映射
DaoMaster master = new DaoMaster(db);
// 管理特定模式下的所有 DAO 对象，并提供一些通用的 CRUD 持久化方法
DaoSession session = master.newSession();
// 得到指定的 StudentDao 对象
StudentDao dao = session.getStudentDao();
dao.insert(student);
//...
五、实战
1、我们写一个简单的实体类（User），测试一下
package com.example.zhangruirui;import org.greenrobot.greendao.annotation.Entity;
import org.greenrobot.greendao.annotation.Generated;
import org.greenrobot.greendao.annotation.Id;@Entity
public class User {@Idprivate long id;private String name;private int age;@Generated(hash = 446251977)public User(long id, String name, int age) {this.id = id;this.name = name;this.age = age;}@Generated(hash = 586692638)public User() {}public long getId() {return id;}public void setId(long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}
}
2、点击 Make Project（或者 Make Moudle ‘App’） 编译一下工程 。如果配置正确，会在配置的包目录下自动会生成 DaoMaster，DaoSession 和 UserDao 类 。
3、然后我们定义 OpenHelper 类：UserDBOpenHelper
package com.example.zhangruirui.greendao;import android.content.Context;
import android.database.sqlite.SQLiteDatabase;import com.example.zhangruirui.DaoMaster;public class UserDBOpenHelper extends DaoMaster.DevOpenHelper {public UserDBOpenHelper(Context context, String name) {super(context, name);}public UserDBOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {super(context, name, factory);}@Overridepublic void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {DaoMaster.dropAllTables(wrap(db), true);}
}
4、然后，类似 SQLite ，我们需要定义 DBManager：UserManager 创建单例实例，来供外部操作数据库
package com.example.zhangruirui.greendao;import android.content.Context;
import android.support.annotation.WorkerThread;import com.google.gson.Gson;import java.io.Serializable;
import java.lang.reflect.Type;public class UserManager {private volatile static UserManager mInstance = null;private Context mContext;private UserStorage mUserStorage = new UserStorage(mContext);private UserManager() {}public static UserManager getInstance() {if (mInstance == null) {synchronized (UserManager.class) {if (mInstance == null) {mInstance = new UserManager();}}}return mInstance;}public <T> T getUserAge(String key, Type typeOfT) {try {String json = mUserStorage.getUserAge(key);Gson gson = new Gson();CacheEntry entry = gson.fromJson(json, CacheEntry.class);return gson.fromJson(entry.mJson, typeOfT);} catch (Exception e) {e.printStackTrace();}return null;}@WorkerThreadpublic void setUserAge(String key, Object entity, Type type) {setUserInner(key, entity, type);}@WorkerThreadprivate void setUserInner(String key, Object entity, Type type) {Gson gson = new Gson();String json = gson.toJson(entity, type);CacheEntry entry = new CacheEntry(json);json = gson.toJson(entry, CacheEntry.class);if (entity == null) {mUserStorage.removeUser(key);} else {mUserStorage.addUser(key, json);}}static class CacheEntry implements Serializable {final String mJson;CacheEntry(String json) {mJson = json;}}
}5、获取 UserDao 对数据库表进行 CRUD 操作即可：UserStorage
package com.example.zhangruirui.greendao;import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.support.annotation.WorkerThread;import com.example.zhangruirui.User;import org.greenrobot.greendao.query.DeleteQuery;
import org.greenrobot.greendao.query.QueryBuilder;public class UserStorage {private SQLiteDatabase mDatabase;private UserDao mUserDao; // 获取 dao 对象private final static String DB_NAME = "user_name_age.db"; // 定义数据库名// 获取核心类的实例UserStorage(Context context) {DaoMaster.OpenHelper helper = new UserDBOpenHelper(context, DB_NAME, null);try {mDatabase = helper.getWritableDatabase();DaoMaster daoMaster = new DaoMaster(mDatabase);DaoSession daoSession = daoMaster.newSession();mUserDao = daoSession.getUserDao();} catch (Exception e) {e.printStackTrace();}}public User getUserByName(String name) {if (!isDataBaseValid()) {return null;}return mUserDao.queryBuilder().where(UserDao.Properties.Name.eq(name)).unique();}/*** 根据用户的名字删除对应的记录*/public void removeUser(String name) {if (!isDataBaseValid()) {return;}try {QueryBuilder<User> qb = mUserDao.queryBuilder();DeleteQuery<User> bd = qb.where(UserDao.Properties.Name.eq(name)).buildDelete();bd.executeDeleteWithoutDetachingEntities();} catch (Exception e) {e.printStackTrace();}}/*** 新增记录，如果存在则更新，不存在直接插入*/@WorkerThreadpublic synchronized void addUser(String name, String json) {if (!isDataBaseValid()) {return;}try {User user = new User();user.setName(name);user.setAge(json);/*** 解决 Exception：* Cannot update entity without key - was it inserted before?*/User oldUser = getUserByName(name);if (oldUser != null) {user.setId(oldUser.getId());}// mUserDao.save(user);if (getUserByName(name) == null) {mUserDao.insert(user);} else {mUserDao.update(user);}} catch (Exception e) {e.printStackTrace();}}/*** 删除所有数据*/@WorkerThreadpublic synchronized void deleteAll() {mUserDao.deleteAll();}private boolean isDataBaseValid() {return mUserDao != null;}public String getUserAge(String key) {return mUserDao.queryBuilder().where(UserDao.Properties.Name.eq(key)).list().get(0).getAge();}
}六、注解
@Entity
表明这个实体类会在数据库中生成一个与之相对应的表
@Entity(// If you have more than one schema, you can tell greenDAO// to which schema an entity belongs (pick any string as a name).schema = "myschema",// Flag to make an entity "active": Active entities have update,// delete, and refresh methods.active = true,// Specifies the name of the table in the database.// By default, the name is based on the entities class name.nameInDb = "AWESOME_USERS",// Define indexes spanning multiple columns here.indexes = {@Index(value = "name DESC", unique = true)},// Flag if the DAO should create the database table (default is true).// Set this to false, if you have multiple entities mapping to one table,// or the table creation is done outside of greenDAO.createInDb = false,// Whether an all properties constructor should be generated.// A no-args constructor is always required.generateConstructors = true,// Whether getters and setters for properties should be generated if missing.generateGettersSetters = true
)
public class User {...
}
@Id(autoincrement = true)
对应数据表中的 Id 字段，主键，必须为 Long 型
如果需要使用主键自增，此时 id 类型为 Long（注意是大写的）
/*** Marks field is the primary key of the entity's table*/
@Retention(RetentionPolicy.SOURCE)
@Target(ElementType.FIELD)
public @interface Id {/*** Specifies that id should be auto-incremented (works only for Long/long fields)* Autoincrement on SQLite introduces additional resources usage and usually can be avoided* @see <a href="https://www.sqlite.org/autoinc.html">SQLite documentation</a>*/boolean autoincrement() default false;
}
@Transient
添加此标记后不会生成数据库表的列，仅仅作为一个普通的 java 类字段，用来临时存储数据的，不会被持久化
@Unique
表名该属性在数据库中只能有唯一值
@Index(unique = true)
七、重要的 api 方法
注意：这些 api 方法中，提到的 key，都是指的主键 Long id
1、查询
http://greenrobot.org/greendao/documentation/queries/
https://juejin.im/post/5abf6ef9f265da2396128456
QueryBuilder.java
2、插入
/*** Insert an entity into the table associated with a concrete DAO.** @return row ID of newly inserted entity*/public long insert(T entity) {return executeInsert(entity, statements.getInsertStatement(), true);}
3、更新
public void update(T entity) {assertSinglePk();DatabaseStatement stmt = statements.getUpdateStatement();if (db.isDbLockedByCurrentThread()) {synchronized (stmt) {if (isStandardSQLite) {updateInsideSynchronized(entity, (SQLiteStatement) stmt.getRawStatement(), true);} else {updateInsideSynchronized(entity, stmt, true);}}} else {// Do TX to acquire a connection before locking the stmt to avoid deadlocksdb.beginTransaction();try {synchronized (stmt) {updateInsideSynchronized(entity, stmt, true);}db.setTransactionSuccessful();} finally {db.endTransaction();}}}
4、插入or更新
public long insertOrReplace(T entity) {return executeInsert(entity, statements.getInsertOrReplaceStatement(), true);}private long executeInsert(T entity, DatabaseStatement stmt, boolean setKeyAndAttach) {long rowId;if (db.isDbLockedByCurrentThread()) {rowId = insertInsideTx(entity, stmt);} else {// Do TX to acquire a connection before locking the stmt to avoid deadlocksdb.beginTransaction();try {rowId = insertInsideTx(entity, stmt);db.setTransactionSuccessful();} finally {db.endTransaction();}}if (setKeyAndAttach) {updateKeyAfterInsertAndAttach(entity, rowId, true);}return rowId;}
save() 方法：
通过 key 属性判断是否存在，如果存在就更新数据，如果 key 为 null 就插入。这里的 key 是什么东东？这就是我今天被坑的地方，这个 key 就是 Long id 这个字段，也就是表中的主键！！！
/*** "Saves" an entity to the database: depending on the existence of the key property, it will be inserted* (key is null) or updated (key is not null).* <p>* This is similar to {@link #insertOrReplace(Object)}, but may be more efficient, because if a key is present,* it does not have to query if that key already exists.*/public void save(T entity) {if (hasKey(entity)) {update(entity);} else {insert(entity);}}
5、删除
/** Deletes the given entity from the database. Currently, only single value PK entities are supported. */public void delete(T entity) {assertSinglePk();K key = getKeyVerified(entity);deleteByKey(key);}
八、入坑系列
1、https://www.jianshu.com/p/7bb9693ea380
2、https://blog.csdn.net/anyanyan07/article/details/73410053
3、打包混淆问题(打包后的 APK，使用不了)： 打包后使用不了，debug 能使用，很明显，混淆的问题。报错如下：
https://blog.csdn.net/ddxxii/article/details/54866871
Caused by: org.greenrobot.greendao.DaoException: Could not init DAOConfig
解决办法：
针对 GreenDao 3.0 ，使用时，发布包需要设置混淆
#greendao
-keep class org.greenrobot.greendao.**{*;}
-keep public interface org.greenrobot.greendao.**
-keepclassmembers class * extends org.greenrobot.greendao.AbstractDao {
public static java.lang.String TABLENAME;
}
-keep class **$Properties#optional
-keep class net.sqlcipher.database.**{*;}
-keep public interface net.sqlcipher.database.**
-dontwarn net.sqlcipher.database.**
-dontwarn org.greenrobot.greendao.**
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