20180502_从零开始的android持久库room其一
16lz
2021-01-23
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）
- Insert
- Delete
- Select
- Update
- 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}@Daopublic interface StudentDAO { @Query("SELECT * FROM student") Single> getAll(); @Query("SELECT * FROM student WHERE uid IN (:ids)") Single> loadAllByIds(int[] ids); @Query("SELECT * FROM student WHERE uid = :id") Single findById(int id); @Query("SELECT * FROM student WHERE first_name LIKE :first AND " + "last_name LIKE :last LIMIT 1") Maybe findByName(String first, String last); @Insert List 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> callable = () -> App.getDb().studentDao().insertAll(s);Single.fromCallable(callable) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(new SingleObserver>() { @Override public void onSubscribe(Disposable d) { } @Override public void onSuccess(List 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>() { @Override public void onSubscribe(Disposable d) { } @Override public void onSuccess(List 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
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