Rxjava2_Flowable_Sqlite_Android数据库访问实例

一、使用Rxjava访问数据库的优点：

1.随意的线程控制，数据库操作在一个线程，返回数据处理在ui线程

2.随时订阅和取消订阅，而不必再使用回调函数

3.对读取的数据用rxjava进行过滤，流式处理

4.使用sqlbrite可以原生返回rxjava的格式，同时是响应式数据库框架

（有数据添加和更新时自动调用之前订阅了的读取函数，达到有数据添加自动更新ui的效果，

同时这个特性没有禁止的方法，只能通过取消订阅停止这个功能，对于有的框架这反而是一种累赘）

二、接下来之关注实现过程：

本次实现用rxjava2的Flowable，有被压支持（在不需要被压支持的情况建议使用Observable）

实现一个稳健的的可灵活切换其他数据库的结构，当然是先定义数据库访问接口。然后跟具不同的数据库实现接口的方法

定义接口：（对于update，delete，insert，可以选择void类型，来简化调用代码，但缺少了执行结果判断）

public interface DbSource { 
  //String sql = "insert into table_task (tid,startts) values(tid,startts)"; 
  Flowable<Boolean> insertNewTask(int tid, int startts); 
 
  //String sql = "select * from table_task"; 
  Flowable<List<TaskItem>> getAllTask(); 
 
  //String sql = "select * from table_task where endts = 0"; 
  Flowable<Optional<TaskItem>> getRunningTask(); 
 
  //String sql = "update table_task set isuploadend=isuploadend where tid=tid"; 
  Flowable<Boolean> markUploadEnd(int tid, boolean isuploadend); 
 
  //String sql = "delete from table_task where tid=tid and endts>0"; 
  Flowable<Boolean> deleteTask(int tid); 
} 

三、用Android原生的Sqlite实现数据库操作

public class SimpleDb implements DbSource { 
 
 private static SimpleDb sqlite; 
 private SqliteHelper sqliteHelper; 
 
 private SimpleDb(Context context) { 
  this.sqliteHelper = new SqliteHelper(context); 
 } 
 
 public static synchronized SimpleDb getInstance(Context context) { 
  if (sqlite == null ) 
   sqlite = new SimpleDb(context); 
  return sqlite; 
 } 
 
 Flowable<Boolean> insertNewTask(int tid, int startts) { 
  return Flowable.create(new FlowableOnSubscribe<Boolean>() { 
   @Override 
   public void subscribe(FlowableEmitter<Boolean> e) throws Exception { 
    //这里数据库操作只做示例代码，主要关注rxjava的Flowable使用方法 
    ContentValues values = new ContentValues(); 
    values.put(“tid”， 1); 
    values.put(“startts”，13233); 
    if(sqliteHelper.getWriteableDatabase().insert(TABLE_NAME, null, values) != -1) 
     e.onNext(true); 
    else 
     e.onNext(false); 
    e.onComplete(); 
   } 
  }, BackpressureStrategy.BUFFER); 
 } 
 
 Flowable<List<TaskItem>> getAllTask() { 
  return Flowable.create(new FlowableOnSubscribe<List<TaskItem>>() { 
   @Override 
   public void subscribe(FlowableEmitter<List<TaskItem>> e) throws Exception { 
 
    List<TaskItem> taskList = new ArrayList<>(); 
    StringBuilder sql = new StringBuilder(100); 
    sql.append("select * from "); 
    sql.append(SqliteHelper.TABLE_NAME_TASK); 
 
    SQLiteDatabase sqLiteDatabase = sqliteHelper.getReadableDatabase(); 
    Cursor cursor = sqLiteDatabase.rawQuery(sql.toString(), null); 
    if (cursor.moveToFirst()) { 
     int count = cursor.getCount(); 
     for (int a = 0; a < count; a ++) { 
      TaskItem item = new TaskItem(); 
      item.setTid(cursor.getInt(1)); 
      item.setStartts(cursor.getInt(2)); 
      item.setEndts(cursor.getInt(3)); 
      taskList.add(item); 
      cursor.move(1); 
     } 
    } 
    cursor.close(); 
    sqLiteDatabase.close(); 
 
    e.onNext(taskList); 
    e.onComplete(); 
   } 
  }, BackpressureStrategy.BUFFER); 
 } 
  
 Flowable<Optional<TaskItem>> getRunningTask() { 
  return Flowable.create(new FlowableOnSubscribe<Optional<TaskItem>>() { 
   @Override 
   public void subscribe(FlowableEmitter<Optional<TaskItem>> e) throws Exception { 
    TaskItem item = null; 
    StringBuilder sql = new StringBuilder(100); 
    sql.append("select * from "); 
    sql.append(SqliteHelper.TABLE_NAME_TASK); 
    sql.append(" where endts=0 limit 1"); 
    SQLiteDatabase sqLiteDatabase = sqliteHelper.getReadableDatabase(); 
    Cursor cursor = sqLiteDatabase.rawQuery(sql.toString(), null); 
    if (cursor.moveToFirst()) { 
     int count = cursor.getCount(); 
     if (count == 1) { 
      item = new TaskItem(); 
      item.setId(cursor.getInt(0)); 
      item.setTid(cursor.getInt(1)); 
      item.setStartts(cursor.getInt(2)); 
      item.setEndts(cursor.getInt(3)); 
     } 
    } 
    cursor.close(); 
    sqLiteDatabase.close(); 
 
    e.onNext(Optional.fromNullable(item)); //import com.google.common.base.Optional;//安全检查，待会看调用的代码，配合rxjava很好 
    e.onComplete(); 
   } 
  }, BackpressureStrategy.BUFFER); 
 } 
  
 Flowable<Boolean> markUploadEnd(int tid, boolean isuploadend) { 
   return Flowable.create(new FlowableOnSubscribe<Boolean>() { 
   @Override 
   public void subscribe(FlowableEmitter<Boolean> e) throws Exception { 
    //这里数据库操作只做示例代码，主要关注rxjava的Flowable使用方法 
    //数据库操作代码 
    e.onNext(false);//返回结果 
    e.onComplete();//返回结束 
   } 
  }, BackpressureStrategy.BUFFER); 
 } 
 
   
 Flowable<Boolean> deleteTask(int tid) { 
  return Flowable.create(new FlowableOnSubscribe<Boolean>() { 
   @Override 
   public void subscribe(FlowableEmitter<Boolean> e) throws Exception { 
    //这里数据库操作只做示例代码，主要关注rxjava的Flowable使用方法 
    //数据库操作代码 
    e.onNext(false);//返回结果 
    e.onComplete();//返回结束 
   } 
  }, BackpressureStrategy.BUFFER); 
 } 
} 

四、同一个接口使用sqlbrite的实现方式

public class BriteDb implements DbSource { 
 @NonNull 
 protected final BriteDatabase mDatabaseHelper; 
 @NonNull 
 private Function<Cursor, TaskItem> mTaskMapperFunction; 
 @NonNull 
 private Function<Cursor, PoiItem> mPoiMapperFunction; 
 @NonNull 
 private Function<Cursor, InterestPoiItem> mInterestPoiMapperFunction; 
 // Prevent direct instantiation. 
 private BriteDb(@NonNull Context context) { 
  DbHelper dbHelper = new DbHelper(context); 
  SqlBrite sqlBrite = new SqlBrite.Builder().build(); 
  mDatabaseHelper = sqlBrite.wrapDatabaseHelper(dbHelper, Schedulers.io(); 
  mTaskMapperFunction = this::getTask; 
  mPoiMapperFunction = this::getPoi; 
  mInterestPoiMapperFunction = this::getInterestPoi; 
 } 
 
 @Nullable 
 private static BriteDb INSTANCE; 
 public static BriteDb getInstance(@NonNull Context context) { 
  if (INSTANCE == null) { 
   INSTANCE = new BriteDb(context); 
  } 
  return INSTANCE; 
 } 
 
 @NonNull 
 private TaskItem getTask(@NonNull Cursor c) { 
  TaskItem item = new TaskItem(); 
  item.setId(c.getInt(c.getColumnIndexOrThrow(PersistenceContract.TaskEntry.COLUMN_TASK_ID))); 
  item.setTid(c.getInt(c.getColumnIndexOrThrow(PersistenceContract.TaskEntry.COLUMN_TASK_TID))); 
  item.setStartts(c.getInt(c.getColumnIndexOrThrow(PersistenceContract.TaskEntry.COLUMN_TASK_STARTTS))); 
  item.setEndts(c.getInt(c.getColumnIndexOrThrow(PersistenceContract.TaskEntry.COLUMN_TASK_ENDTS))); 
  return item; 
 } 
  
 @Override 
 public void insertNewTask(int tid, int startts) { 
  ContentValues values = new ContentValues(); 
  values.put(PersistenceContract.TaskEntry.COLUMN_TASK_TID, tid); 
  values.put(PersistenceContract.TaskEntry.COLUMN_TASK_STARTTS, startts); 
  mDatabaseHelper.insert(PersistenceContract.TaskEntry.TABLE_NAME_TASK, values, SQLiteDatabase.CONFLICT_REPLACE); 
 } 
 
 @Override 
 public Flowable<List<TaskItem>> getAllTask() { 
  String sql = String.format("SELECT * FROM %s", PersistenceContract.TaskEntry.TABLE_NAME_TASK);//TABLE_NAME_TASK表的名字字符串 
  return mDatabaseHelper.createQuery(PersistenceContract.TaskEntry.TABLE_NAME_TASK, sql) 
    .mapToList(mTaskMapperFunction) 
    .toFlowable(BackpressureStrategy.BUFFER); 
 } 
 
 @Override 
 public Flowable<Optional<TaskItem>> getRunningTask() { 
  String sql = String.format("SELECT * FROM %s WHERE %s = ? limit 1", 
    PersistenceContract.TaskEntry.TABLE_NAME_TASK, PersistenceContract.TaskEntry.COLUMN_TASK_ENDTS); 
  return mDatabaseHelper.createQuery(PersistenceContract.TaskEntry.TABLE_NAME_TASK, sql, "0") 
    .mapToOne(cursor -> Optional.fromNullable(mTaskMapperFunction.apply(cursor))) 
    .toFlowable(BackpressureStrategy.BUFFER); 
 } 
 
 @Override 
 public Flowable<Boolean> markUploadEnd(int tid, boolean isuploadend) { 
  return Flowable.create(new FlowableOnSubscribe<Boolean>() { 
   @Override 
   public void subscribe(FlowableEmitter<Boolean> e) throws Exception { 
     ContentValues values = new ContentValues(); 
     if(isuploadend) { 
      values.put(PersistenceContract.TaskEntry.COLUMN_TASK_ISUPLOADEND, 1); 
     } else { 
      values.put(PersistenceContract.TaskEntry.COLUMN_TASK_ISUPLOADEND, 0); 
     } 
     String selection = PersistenceContract.TaskEntry.COLUMN_TASK_TID + " = ?"; 
     //String[] selectionArgs = {String.valueOf(tid)}; 
     String selectionArgs = String.valueOf(tid); 
     int res = mDatabaseHelper.update(PersistenceContract.TaskEntry.TABLE_NAME_TASK, values, selection, selectionArgs); 
     if (res > 0) { 
      e.onNext(true);//返回结果 
     } else { 
       e.onNext(false);//返回结果 
     } 
     e.onComplete();//返回结束 
   } 
  }, BackpressureStrategy.BUFFER); 
 } 
 
 @Override 
 public Flowable<Boolean> deleteTask(int tid) { 
  return Flowable.create(new FlowableOnSubscribe<Boolean>() { 
   @Override 
   public void subscribe(FlowableEmitter<Boolean> e) throws Exception { 
     String selection = PersistenceContract.TaskEntry.COLUMN_TASK_TID + " = ? AND "+ 
             PersistenceContract.TaskEntry.COLUMN_TASK_ENDTS + " > 0"; 
     String[] selectionArgs = new String[1]; 
     selectionArgs[0] = String.valueOf(tid); 
     int res = mDatabaseHelper.delete(PersistenceContract.TaskEntry.TABLE_NAME_TASK, selection, selectionArgs); 
     if (res > 0) { 
      e.onNext(true);//返回结果 
     } else { 
       e.onNext(false);//返回结果 
     } 
     e.onComplete();//返回结束 
   } 
  }, BackpressureStrategy.BUFFER); 
 } 
} 

五、数据库调用使用方法

使用了lambda简化了表达式进一步简化代码：

简化方法：在/app/build.gradle里面加入如下内容：(defaultConfig的外面)

compileOptions { 
 sourceCompatibility JavaVersion.VERSION_1_8 
 targetCompatibility JavaVersion.VERSION_1_8 
} 

接口调用（获得数据库实例）：

//全局定义的实例获取类，以后想要换数据库，只需在这个类里切换即可 
public class Injection { 
 public static DbSource getDbSource(Context context) { 
  //choose one of them 
  //return BriteDb.getInstance(context); 
  return SimpleDb.getInstance(context); 
 } 
} 
 
DbSource db = Injection.getInstance(mContext); 
 
disposable1 = db.getAllTask() 
       .flatMap(Flowable::fromIterable) 
       .filter(task -> {     //自定义过滤 
         if (!task.getIsuploadend()) { 
          return true; 
         } else { 
          return false; 
         } 
       }) 
       .subscribe(taskItems -> //这里是使用了lambda简化了表达式 
        doTaskProcess(taskItems) 
       , throwable -> { 
        throwable.printStackTrace(); 
       },// onCompleted 
       () -> { 
        if (disposable1 != null && !disposable1.isDisposed()) { 
         disposable1.dispose(); 
        } 
       }); 
 
 disposable1 = db.getRunningTask() 
    .filter(Optional::isPresent) //判断是否为空，为空的就跳过 
    .map(Optional::get)    //获取到真的参数 
    .subscribeOn(Schedulers.io()) 
    .observeOn(AndroidSchedulers.mainThread()) 
    .subscribe(taskItem -> {     //onNext() 
       //has running task 
       mTid = taskItem.getTid(); 
    }, throwable -> throwable.printStackTrace() //onError() 
    , () -> disposable1.dispose());    //onComplete() 
 
disposable1 = db.markUploadEnd(tid, isuploadend) 
    .subscribeOn(Schedulers.io()) 
    .observeOn(AndroidSchedulers.mainThread()) 
    .subscribe(status -> {     //onNext() 
       if (status) { 
        //dosomething 
       } 
    }, throwable -> throwable.printStackTrace() //onError() 
    , () -> disposable1.dispose());    //onComplete() 
 
disposable1 = db.deleteTask(tid) 
    .subscribeOn(Schedulers.io()) 
    .observeOn(AndroidSchedulers.mainThread()) 
    .subscribe(status -> {     //onNext() 
       if (status) { 
        //dosomething 
       } 
    }, throwable -> throwable.printStackTrace() //onError() 
    , () -> disposable1.dispose());    //onComplete() 

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