本文整理自网络，侵删。
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
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数据库系统概念 第6版
本书主要讲述了数据模型、基于对象的数据库和XML、数据存储和查询、事务管理、体系结构等方面的内容。
