20180502_从零开始的android持久库room其一

Room是android的一个持久化库，SQLite的抽象层，便于使用。推荐用Room替代SQLite。

20180502_从零开始的android持久库room其一 引入room库Room的3大组件数据访问（增删查改） InsertDeleteSelectUpdate 注意事项源码地址参考文章

引入room库

在project的gradle中加入google仓库

allprojects { repositories { jcenter() google() } }

在app的gradle中加入room依赖

其中最后3个是用来支持rxjava2的，方便使用

dependencies { // Room (use 1.1.0-beta3 for latest beta) implementation "android.arch.persistence.room:runtime:1.0.0" annotationProcessor "android.arch.persistence.room:compiler:1.0.0" // RxJava support for Room (use 1.1.0-beta3 for latest beta) implementation "android.arch.persistence.room:rxjava2:1.0.0" implementation 'io.reactivex.rxjava2:rxandroid:2.0.2' implementation "io.reactivex.rxjava2:rxjava:2.1.13" }

初始化

在Application中初始化数据库，记得在AndroidManifest.xml中配置App

public class App extends Application { private static App instance; private static AppDatabase db; @Override public void onCreate() { super.onCreate(); instance = this; initDb(); } private void initDb() { // 这里初始化room db = Room.databaseBuilder(this, AppDatabase.class, "database-name").build(); } public static App getInstance() { return instance; } public static AppDatabase getDb() { return db; } }

Room的3大组件

Database 数据库Entity 实体类DAO 数据访问对象

概念不是很难，直接看代码更加方便

@Database(entities = {Student.class}, version = 1) // 数据库注解，必须。entities指定实体类，version指定数据库版本 public abstract class AppDatabase extends RoomDatabase { public abstract StudentDAO studentDao(); } @Entity // 实体类注解，必须 public class Student { @PrimaryKey(autoGenerate = true) // 主键, autoGenerate表示自增长 private long uid; @ColumnInfo(name = "first_name") // name指定的是表的字段名 private String firstName; @ColumnInfo(name = "last_name") private String lastName; private int age; // 可以不指定ColumnInfo，那么表的字段名和属性名一致 // ... get set略 } @Dao public interface StudentDAO { @Query("SELECT * FROM student") Single<List<Student>> getAll(); @Query("SELECT * FROM student WHERE uid IN (:ids)") Single<List<Student>> loadAllByIds(int[] ids); @Query("SELECT * FROM student WHERE uid = :id") Single<Student> findById(int id); @Query("SELECT * FROM student WHERE first_name LIKE :first AND " + "last_name LIKE :last LIMIT 1") Maybe<Student> findByName(String first, String last); @Insert List<Long> insertAll(Student... students); @Update void update(Student student); @Delete void delete(Student student); }

数据访问（增删查改）

Insert

Student s = new Student(); s.setFirstName(firstName); s.setLastName(lastName); s.setAge(ageInt); Callable<List<Long>> callable = () -> App.getDb().studentDao().insertAll(s); Single.fromCallable(callable) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(new SingleObserver<List<Long>>() { @Override public void onSubscribe(Disposable d) { } @Override public void onSuccess(List<Long> longs) { Log.i(TAG, String.format("onSuccess: insert success ids = %s", Arrays.toString(longs.toArray()))); Snackbar.make(et_first_name, "add student success", Snackbar.LENGTH_SHORT).show(); } @Override public void onError(Throwable e) { Log.e(TAG, "onError: insert error", e); Snackbar.make(et_first_name, "add student fail", Snackbar.LENGTH_SHORT).show(); } });

Delete

final Student s = studentList.get(position); Action action = () -> App.getDb().studentDao().delete(s); Completable.fromAction(action) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(new CompletableObserver() { @Override public void onSubscribe(Disposable d) { } @Override public void onComplete() { Log.i(TAG, String.format("onComplete: delete student success id = %d", s.getUid())); Snackbar.make(rv_list, "delete student success", Snackbar.LENGTH_SHORT).show(); } @Override public void onError(Throwable e) { Log.e(TAG, "onError: delete student fail", e); Snackbar.make(rv_list, "delete student fail", Snackbar.LENGTH_SHORT).show(); } }); } });

Select

App.getDb().studentDao().getAll() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(new SingleObserver<List<Student>>() { @Override public void onSubscribe(Disposable d) { } @Override public void onSuccess(List<Student> students) { Log.i(TAG, String.format("onSuccess: students.size = %d", students.size())); studentList.addAll(students); adapter.notifyDataSetChanged(); } @Override public void onError(Throwable e) { Log.e(TAG, "onError: get all student error", e); Snackbar.make(rv_list, "select student fail", Snackbar.LENGTH_SHORT).show(); } });

Update

Action action = () -> { Student s = new Student(); s.setUid(idInt); if (!TextUtils.isEmpty(firstName)) { s.setFirstName(firstName); } if (!TextUtils.isEmpty(lastName)) { s.setLastName(lastName); } if (!TextUtils.isEmpty(age)) { s.setAge(ageInt); } App.getDb().studentDao().update(s); }; Completable.fromAction(action) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(new CompletableObserver() { @Override public void onSubscribe(Disposable d) { } @Override public void onComplete() { Log.i(TAG, "onComplete: update student success"); Snackbar.make(et_id, "update student success", Snackbar.LENGTH_SHORT).show(); } @Override public void onError(Throwable e) { Log.e(TAG, "onError: update student fail", e); Snackbar.make(et_id, "update student fail", Snackbar.LENGTH_SHORT).show(); } });

到这里，我们已经可以简单的增删查改数据库了。

注意事项

遇到下面的这个警告，说的是找不到地方导出schema

警告: Schema export directory is not provided to the annotation processor so we cannot export the schema. You can either provide `room.schemaLocation` annotation processor argument OR set exportSchema to false.

解决方案

在app的gradle文件中添加

android { // 略 defaultConfig { // 略 // for room, 这里添加room的schemas导出地点 javaCompileOptions { annotationProcessorOptions { arguments = ["room.schemaLocation": "$projectDir/schemas".toString()] } } } // 略 }

源码地址

AndroidRoomStudy

参考文章

android room