Realm快速入门攻略

最近新出来Realm Android，性能口碑都不错，因为项目中需要构建数据库，所以学而记之。

1.安装

   compile 'io.realm:realm-android:0.84.1'

2.模型

/** * Created by wangchang on 2016/6/20. */
public class User extends RealmObject{
    private String          name;
    @PrimaryKey
    private int             age;
    @Ignore
    private int             sessionId;

    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; }
    public int    getSessionId() { return sessionId; }
    public void   setSessionId(int sessionId) { this.sessionId = sessionId; }
}

• Realm 数据模型定义需要继承自 RealmObject 类。
• 支持private，public，protected以及自定义的成员方法。

修饰符:

@Required:
告诉 Realm 强制禁止空值（null）被存储。只有 Boolean、 Byte、 Short、 Integer、 Long、 Float、 Double、 String、 byte[] 以及 Date 可以被 @Required 修饰。在其它类型属性上使用 @Required 修饰会导致编译失败。

@Ignore :
标识不想保存到数据库的字段

@PrimaryKey：
主键

3.写入

• 初始化配置

/** * Created by wangchang on 2016/6/20. */
public class MyApplication extends Application{

    private static MyApplication application;
    private static RealmConfiguration realmConfiguration;

    @Override
    public void onCreate() {
        super.onCreate();
        application=this;
        //方式1
        realmConfiguration = new RealmConfiguration
                .Builder(this)
                .name("known")//设置数据库名称
// .encryptionKey(key)//设置加密
                .build();
        //方式2
       // realmConfiguration = new RealmConfiguration.Builder(application).build();
       // Realm.setDefaultConfiguration(realmConfiguration);
    }
    public static MyApplication getInstance(){
        return application;
    }
    public static RealmConfiguration getRealmConfig(){
        return realmConfiguration;
    }
}

使用：

    private Realm realm;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        realm=Realm.getInstance(MyApplication.getRealmConfig());
        realm=Realm.getDefaultInstance();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        realm.close();
    }
}

写入（增）：

RealmConfiguration realmConfig = new RealmConfiguration.Builder(getApplicationContext()).build();
        Realm.setDefaultConfiguration(realmConfig);

        Realm realm = Realm.getDefaultInstance();
        realm.beginTransaction();
        //创建对象
        User user = realm.createObject(User.class);
        user.setName("www");
        user.setAge(14);
        user.setSessionId(1001);
        realm.commitTransaction();

创建对象createObject/copyToRealm：

User user = new User("John");
user.setEmail("[email protected]");

// Copy the object to Realm. Any further changes must happen on realmUser
realm.beginTransaction();
User realmUser = realm.copyToRealm(user); 
realm.commitTransaction();

写入不提交：

realm.beginWriteTransaction();
//写入
realm.cancelTransaction();

添加json到Realm

public class City extends RealmObject {
    private String city;
    private int id;
    // getters and setters left out ...
}

// Insert from a string
realm.beginTransaction();
realm.createObjectFromJson(City.class, "{ city: \"Copenhagen\", id: 1 }");
realm.commitTransaction();

事务执行块（Transaction blocks）：
使用 realm.executeTransaction() 方法，它会自动处理写入事物的开始和提交，并在错误发生时取消写入事物。

realm.executeTransaction(new Realm.Transaction() {
    @Override
    public void execute(Realm realm) {
        User user = realm.createObject(User.class);
        user.setName("John");
        user.setAge(1);
    }
});

异步事务（Asynchronous Transactions）：
事务会相互阻塞其所在的线程，在后台线程中开启事务进行写入操作可以有效避免 UI 线程被阻塞。通过使用异步事务，Realm 会在后台线程中进行写入操作，并在事务完成时将结果传回调用线程。

realm.executeTransactionAsync(new Realm.Transaction() {
    @Override
    public void execute(Realm bgRealm) {
        User user = bgRealm.createObject(User.class);
        user.setName("John");
        user.setEmail("[email protected]");
    }
}, new Realm.Transaction.OnSuccess() {
    @Override
    public void onSuccess() {
        // Transaction was a success.
    }
}, new Realm.Transaction.OnError() {
    @Override
    public void onError(Throwable error) {
        // Transaction failed and was automatically canceled.
    }
});

在onstop/ondestory中添加：

public void onStop () {
    if (transaction != null && !transaction.isCancelled()) {
        transaction.cancel();
    }
}

查询：

 RealmQuery<User> query = realm.where(User.class);
        query.equalTo("name", "www");
        RealmResults<User> result = query.findAll();
        RealmResults<User> result1 = realm.where(User.class)
                .equalTo("age", "12")
                .findAll();
        Log.e("TAG",result+"//"+result1);

日志：

06-20 17:57:18.195 8545-8545/com.example.com.testrealm E/TAG: [User = [{name:www},{age:12}], User = [{name:www},{age:13}], User = [{name:www},{age:14}], User = [{name:www},{age:15}], User = [{name:www},{age:16}], User = [{name:www},{age:17}], User = [{name:www},{age:18}]]//[User = [{name:www},{age:12}]]

查询支持：

between()、greaterThan()、lessThan()、greaterThanOrEqualTo() 和 lessThanOrEqualTo() equalTo() 和 notEqualTo() contains()、beginsWith() 和 endsWith() isNull() 和 isNotNull() isEmpty() 和 isNotEmpty()

当查询复杂而且耗费大量时间时采用异步查询：

RealmResults<User> result = realm.where(User.class)
                              .equalTo("name", "John")
                              .or()
                              .equalTo("name", "Peter")
                              .findAllAsync();

排序：

RealmResults<User> result = realm.where(User.class).findAll();
result.sort("age"); // 升序
result.sort("age", RealmResults.SORT_ORDER_DESCENDING);//降序

删除：

realm.executeTransaction(new Realm.Transaction() {
            @Override
            public void execute(Realm realm) {
                //刪除第一條
                result.remove(0);
                //删除最后一条
                result.removeLast();
                //删除固定一条
                User user= result.get(0);
                user.removeFromRealm();
                // 清空
                result.clear();

            }
        });

更新修改：

 //更新
        RealmResults<User> results = realm.where(User.class).findAll();
        for (User u : results) {
            u.setName("李四");
            realm.copyToRealmOrUpdate(results);
            realm.commitTransaction();
        }
        //
        RealmResults<User> resultd = realm.where(User.class).findAll();
        for (int i = 0; i < resultd.size(); i++) {
            User u = resultd.get(i);
            u.setName("李四");
            realm.copyToRealmOrUpdate(results);
            realm.commitTransaction();
        }

监听器：
当后台线程向Realm添加数据，您的UI线程或者其它线程可以添加一个监听器来获取数据改变的通知。监听器在Realm数据改变的时候会被触发。

public class MyActivity extends Activity {
    private Realm realm;
    // A reference to RealmChangeListener needs to be held to avoid being
    // removed by the garbage collector.
    private RealmChangeListener realmListener;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      realm = Realm.getDefaultInstance();
      reamlListener = new RealmChangeListener() {
        @Override
        public void onChange() {
            // ... do something with the updates (UI, etc.) ...
        }};
      realm.addChangeListener(realmListener);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        // Remove the listener.
        realm.removeChangeListener(realmListener);
        // Close the realm instance.
        realm.close();
    }
}