Realm学习

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Android数据库Realm学习（一）基本使用
Realm for Android快速入门教程
Realm Android简单使用说明
realm官方文档

http://www.jianshu.com/p/a506ee4afecb

错误记录
1. 同时引用ButterKnife和Realm编译时可能会出现下述错误:

Error:Execution failed for task ':app:transformResourcesWithMergeJavaResForDebug'.

com.android.build.api.transform.TransformException: com.android.builder.packaging.DuplicateFileException: Duplicate files copied in APK META-INF/services/javax.annotation.processing.Processor
File1: C:\Users\Администратор.gradle\caches\modules-2\files-2.1\com.jakewharton\butterknife\7.0.1\d5d13ea991eab0252e3710e5df3d6a9d4b21d461\butterknife-7.0.1.jar
File2: C:\Users\Администратор.gradle\caches\modules-2\files-2.1\io.realm\realm-android\0.86.0\e49a43bcbbc3d5e5491dd2f4d3799a504b618e6b\realm-android-0.86.0.jar

从stackoverflow看到解决方案,在gradle文件中做如下配置:

packagingOptions {
exclude 'META-INF/services/javax.annotation.processing.Processor' 
}

这里记录下,方便大家排查
2.

Gson gson = new GsonBuilder()  
  .setExclusionStrategies(new ExclusionStrategy() {  
    // This is required to make Gson work with RealmObjects  
    @Override public boolean shouldSkipField(FieldAttributes f) {  
      return f.getDeclaringClass().equals(RealmObject.class);  
    }  

    @Override public boolean shouldSkipClass(Class<?> clazz) {  
      return false;  
    }  
  }).create();  

Realm创建
1. 第一步realm每个activity使用都需要初始化，直接在application中初始化他

public class MyApplication extends Application {
  @Override
  public void onCreate() {
    super.onCreate();
    // The realm file will be located in Context.getFilesDir() with name "default.realm"
    RealmConfiguration config = new RealmConfiguration.Builder(this).build();
    Realm.setDefaultConfiguration(config);
  }
}

public class MyActivity extends Activity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Realm realm = Realm.getDefaultInstance();
    // ... Do something ...
    realm.close();
  }
}

• 增

    //添加一条数据到数据库  
        private void realmInsert(Realm realm) {  
            realm.beginTransaction();//必须先开启事务  
            Book book = realm.createObject(Book.class);  
            book.setAuthor("司马迁");  
            book.setName("史记");  
            realm.commitTransaction();//提交事务  
            book = realm.where(Book.class).findFirst();  
        }  

• 查

//查询一个数据库中第一个book  
        Book book = realm.where(Book.class)  
                .equalTo("name","史记")//相当于where name='史记'  
                .or()//或，连接查询条件；没有这个方法时，默认是隐式地被逻辑和(&)组合  
                .equalTo("author","司马迁")//相当于 author='司马迁'  
                .findFirst();  

• 改

    private void realmUpdate(Realm realm){  
            realm.beginTransaction();//开启事务  
            Book b = new Book();//新建实例  
            b.setId(1);//book类新加的int属性，用@PrimaryKey注解作为主键  
            b.setAuthor("simaqian");  
            b.setName("史记");  
            realm.copyToRealmOrUpdate(b);//修改操作  
            realm.commitTransaction();//提交事务  
        }  

• 删

realm.executeTransaction(new Realm.Transaction(){
                        @Override
                        public void execute(Realm realm) {
                            RealmResults<GankDataBean>results = realm.where(GankDataBean.class).equalTo("type", mType).findAll();
                            results.clear();
                        }
                    });