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ROOM数据库快速入门

第一章 准备工作

第01节 引入库

build.gradle 文件当中添加

// 采用 Room 数据库的库
def room_version = "2.4.2" // 请检查最新版本
implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version" // 对于 Java// 采用rxjava的库（涉及到主线程和子线程的切换操作）
implementation 'io.reactivex.rxjava2:rxjava:2.2.19'
implementation 'io.reactivex.rxjava2:rxandroid:2.1.1'

第02节 布局文件

<androidx.appcompat.widget.LinearLayoutCompatandroid:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical"><androidx.appcompat.widget.AppCompatButtonandroid:id="@+id/button_insert_dept"android:layout_width="match_parent"android:layout_height="wrap_content"android:padding="10dp"android:text="添加数据 - 部门" /><androidx.appcompat.widget.AppCompatButtonandroid:id="@+id/button_delete_dept"android:layout_width="match_parent"android:layout_height="wrap_content"android:padding="10dp"android:text="删除数据 - 部门" /><androidx.appcompat.widget.AppCompatButtonandroid:id="@+id/button_update_dept"android:layout_width="match_parent"android:layout_height="wrap_content"android:padding="10dp"android:text="修改数据 - 部门" /><androidx.appcompat.widget.AppCompatButtonandroid:id="@+id/button_query_dept"android:layout_width="match_parent"android:layout_height="wrap_content"android:padding="10dp"android:text="查询数据 - 部门" /><androidx.appcompat.widget.AppCompatButtonandroid:id="@+id/button_insert_employee"android:layout_width="match_parent"android:layout_height="wrap_content"android:padding="10dp"android:text="添加数据 - 员工" /><androidx.appcompat.widget.AppCompatButtonandroid:id="@+id/button_delete_employee"android:layout_width="match_parent"android:layout_height="wrap_content"android:padding="10dp"android:text="删除数据 - 员工" /><androidx.appcompat.widget.AppCompatButtonandroid:id="@+id/button_update_employee"android:layout_width="match_parent"android:layout_height="wrap_content"android:padding="10dp"android:text="修改数据 - 员工" /><androidx.appcompat.widget.AppCompatButtonandroid:id="@+id/button_query_employee"android:layout_width="match_parent"android:layout_height="wrap_content"android:padding="10dp"android:text="查询数据 - 员工" /><androidx.appcompat.widget.AppCompatTextViewandroid:id="@+id/text_view_show"android:layout_width="match_parent"android:layout_height="wrap_content" /></androidx.appcompat.widget.LinearLayoutCompat>

第03节 activity类

public class DemoTestActivity extends AppCompatActivity {private final Context context = DemoTestActivity.this;private AppCompatButton buttonInsertDept;private AppCompatButton buttonDeleteDept;private AppCompatButton buttonUpdateDept;private AppCompatButton buttonQueryDept;private AppCompatButton buttonInsertEmployee;private AppCompatButton buttonDeleteEmployee;private AppCompatButton buttonUpdateEmployee;private AppCompatButton buttonQueryEmployee;private AppCompatTextView textViewShow;private final Random random = new Random();private int indexDept = 1;private int indexEmployee = 1;private EntityService service;@Overrideprotected void onCreate(@Nullable Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_demo_test);buttonInsertDept = findViewById(R.id.button_insert_dept);buttonDeleteDept = findViewById(R.id.button_delete_dept);buttonUpdateDept = findViewById(R.id.button_update_dept);buttonQueryDept = findViewById(R.id.button_query_dept);buttonInsertEmployee = findViewById(R.id.button_insert_employee);buttonDeleteEmployee = findViewById(R.id.button_delete_employee);buttonUpdateEmployee = findViewById(R.id.button_update_employee);buttonQueryEmployee = findViewById(R.id.button_query_employee);textViewShow = findViewById(R.id.text_view_show);service = new EntityServiceImpl(context);// 初始化监听器initListener();}private void initListener() {buttonInsertDept.setOnClickListener(v -> {EntityDept dept = new EntityDept();dept.setDeptName("部门名称-" + indexDept);dept.setDeptNo(String.valueOf(indexDept));indexDept++;service.insertDept(dept).observeOn(AndroidSchedulers.mainThread()).subscribeOn(Schedulers.io()).subscribe(new CompletableObserver() {@Overridepublic void onSubscribe(Disposable d) {}@Overridepublic void onComplete() {}@Overridepublic void onError(Throwable e) {}});});buttonDeleteDept.setOnClickListener(v -> {service.deleteDept(1).observeOn(AndroidSchedulers.mainThread()).subscribeOn(Schedulers.io()).subscribe(new CompletableObserver() {@Overridepublic void onSubscribe(Disposable d) {}@Overridepublic void onComplete() {}@Overridepublic void onError(Throwable e) {}});});buttonUpdateDept.setOnClickListener(v -> {service.updateDeptName(2, "人事部").observeOn(AndroidSchedulers.mainThread()).subscribeOn(Schedulers.io()).subscribe(new CompletableObserver() {@Overridepublic void onSubscribe(Disposable d) {}@Overridepublic void onComplete() {}@Overridepublic void onError(Throwable e) {}});});buttonQueryDept.setOnClickListener(v -> {service.findAllDept().observeOn(AndroidSchedulers.mainThread()).subscribeOn(Schedulers.io()).subscribe(new Observer<List<EntityDept>>() {@Overridepublic void onSubscribe(Disposable d) {}@Overridepublic void onNext(List<EntityDept> entityDeptList) {StringBuilder sb = new StringBuilder();for (EntityDept dept : entityDeptList) {sb.append(dept.getId()).append("\t");sb.append(dept.getDeptNo()).append("\t");sb.append(dept.getDeptName()).append("\n");}textViewShow.setText(sb);}@Overridepublic void onError(Throwable e) {}@Overridepublic void onComplete() {}});});buttonInsertEmployee.setOnClickListener(v -> {EntityEmployee employee = new EntityEmployee();employee.setName("员工名称-" + indexEmployee);employee.setAge(random.nextInt(20));employee.setEmployeeDeptId(random.nextInt(5));indexEmployee++;service.insertEmployee(employee).observeOn(AndroidSchedulers.mainThread()).subscribeOn(Schedulers.io()).subscribe(new CompletableObserver() {@Overridepublic void onSubscribe(Disposable d) {}@Overridepublic void onComplete() {}@Overridepublic void onError(Throwable e) {}});});buttonDeleteEmployee.setOnClickListener(v -> {service.deleteEmployee(1).observeOn(AndroidSchedulers.mainThread()).subscribeOn(Schedulers.io()).subscribe(new CompletableObserver() {@Overridepublic void onSubscribe(Disposable d) {}@Overridepublic void onComplete() {}@Overridepublic void onError(Throwable e) {}});});buttonUpdateEmployee.setOnClickListener(v -> {service.updateEmployeeName(2, "孙悟空").observeOn(AndroidSchedulers.mainThread()).subscribeOn(Schedulers.io()).subscribe(new CompletableObserver() {@Overridepublic void onSubscribe(Disposable d) {}@Overridepublic void onComplete() {}@Overridepublic void onError(Throwable e) {}});});buttonQueryEmployee.setOnClickListener(v -> {service.findAllEmployee().observeOn(AndroidSchedulers.mainThread()).subscribeOn(Schedulers.io()).subscribe(new Observer<List<EntityEmployee>>() {@Overridepublic void onSubscribe(Disposable d) {}@Overridepublic void onNext(List<EntityEmployee> entityEmployeeList) {StringBuilder sb = new StringBuilder();for (EntityEmployee employee : entityEmployeeList) {sb.append(employee.getId()).append("\t");sb.append(employee.getName()).append("\t");sb.append(employee.getAge()).append("\t");sb.append(employee.getEmployeeDeptId()).append("\n");}textViewShow.setText(sb);}@Overridepublic void onError(Throwable e) {}@Overridepublic void onComplete() {}});});}
}

第04节 效果图

第一张表 和 数据库地址

第二张表 和 布局UI

备注：

​ 1、这里阅读数据库，采用的是 SQLiteStudio

​ 2、必须将 databases 当中的三个文件都导出，才能看到表结构

SQLiteStudio 的下载地址

https://github.com/pawelsalawa/sqlitestudio/releases

第二章 数据类

第01节 实体类（表）

表（部门）实体类

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;@Entity(tableName = "t_dept")
public class EntityDept {// 主键 自增长@PrimaryKey(autoGenerate = true)private int id;// 用户名@ColumnInfo(name = "dept_name")private String deptName;// 部门编号@ColumnInfo(name = "dept_no")private String deptNo;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getDeptName() {return deptName;}public void setDeptName(String deptName) {this.deptName = deptName;}public String getDeptNo() {return deptNo;}public void setDeptNo(String deptNo) {this.deptNo = deptNo;}
}

表（员工）实体类

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;@Entity(tableName = "t_employee")
public class EntityEmployee {// 主键 自增长@PrimaryKey(autoGenerate = true)private int id;// 员工姓名@ColumnInfo(name = "employee_name")private String name;// 员工年龄@ColumnInfo(name = "employee_age")private int age;// 所在部门的ID@ColumnInfo(name = "emp_dept_id")private int employeeDeptId;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public int getEmployeeDeptId() {return employeeDeptId;}public void setEmployeeDeptId(int employeeDeptId) {this.employeeDeptId = employeeDeptId;}
}

第02节 数据访问类（DAO）

import androidx.room.Dao;
import androidx.room.Insert;
import androidx.room.Query;import java.util.List;// DAO (Data Access Object) 提供了访问数据库的方法
@Dao
public interface EntityDao {// 增：添加部门信息@Insertvoid insertDept(EntityDept dept);// 删：删除数据@Query("DELETE FROM t_dept WHERE id = :deptId")void deleteDept(int deptId);// 改：修改数据@Query("UPDATE t_dept SET dept_name = :deptName WHERE dept_no = :deptNo")void updateDeptName(int deptNo, String deptName);// 查：查询数据@Query("SELECT * FROM t_dept")List<EntityDept> findAllDept();// 增：添加员工信息@Insertvoid insertEmployee(EntityEmployee employee);// 删：删除数据@Query("DELETE FROM t_employee WHERE id = :employeeId")void deleteEmployee(int employeeId);// 改：修改数据@Query("UPDATE t_employee SET employee_name = :employeeName WHERE id = :employeeId")void updateEmployeeName(int employeeId, String employeeName);// 查：查询数据@Query("SELECT * FROM t_employee")List<EntityEmployee> findAllEmployee();
}

第03节 数据Service层

接口

import java.util.List;import io.reactivex.Completable;
import io.reactivex.Observable;public interface EntityService {// 增：添加部门信息Completable insertDept(EntityDept dept);// 删：删除数据Completable deleteDept(int deptId);// 改：修改数据Completable updateDeptName(int deptNo, String deptName);// 查：查询数据Observable<List<EntityDept>> findAllDept();// 增：添加员工信息Completable insertEmployee(EntityEmployee employee);// 删：删除数据Completable deleteEmployee(int employeeId);// 改：修改数据Completable updateEmployeeName(int employeeId, String employeeName);// 查：查询数据Observable<List<EntityEmployee>> findAllEmployee();
}

实现类

import android.content.Context;import java.util.List;import io.reactivex.Completable;
import io.reactivex.Observable;public class EntityServiceImpl implements EntityService {private Context context;public EntityServiceImpl(Context context) {this.context = context;}@Overridepublic Completable insertDept(EntityDept dept) {return Completable.create(emitter -> {AppDataBase.getDataBase(context).entityDao().insertDept(dept);emitter.onComplete();});}@Overridepublic Completable deleteDept(int deptId) {return Completable.create(emitter -> {AppDataBase.getDataBase(context).entityDao().deleteDept(deptId);emitter.onComplete();});}@Overridepublic Completable updateDeptName(int deptNo, String deptName) {return Completable.create(emitter -> {AppDataBase.getDataBase(context).entityDao().updateDeptName(deptNo, deptName);emitter.onComplete();});}@Overridepublic Observable<List<EntityDept>> findAllDept() {return Observable.create(emitter -> {List<EntityDept> list = AppDataBase.getDataBase(context).entityDao().findAllDept();emitter.onNext(list);emitter.onComplete();});}@Overridepublic Completable insertEmployee(EntityEmployee employee) {return Completable.create(emitter -> {AppDataBase.getDataBase(context).entityDao().insertEmployee(employee);emitter.onComplete();});}@Overridepublic Completable deleteEmployee(int employeeId) {return Completable.create(emitter -> {AppDataBase.getDataBase(context).entityDao().deleteEmployee(employeeId);emitter.onComplete();});}@Overridepublic Completable updateEmployeeName(int employeeId, String employeeName) {return Completable.create(emitter -> {AppDataBase.getDataBase(context).entityDao().updateEmployeeName(employeeId, employeeName);emitter.onComplete();});}@Overridepublic Observable<List<EntityEmployee>> findAllEmployee() {return Observable.create(emitter -> {List<EntityEmployee> list = AppDataBase.getDataBase(context).entityDao().findAllEmployee();emitter.onNext(list);emitter.onComplete();});}
}

第04节 RoomDataBase 类

import android.content.Context;import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;// RoomDataBase
@Database(entities = {EntityDept.class, EntityEmployee.class}, version = 1)
public abstract class AppDataBase extends RoomDatabase {private static final String DATA_BASE_NAME = "my_database.db";private static volatile AppDataBase INSTANCE;// 获取到 EntityDao 的对象public abstract EntityDao entityDao();public static AppDataBase getDataBase(Context context) {if (INSTANCE == null) {synchronized (AppDataBase.class) {if (INSTANCE == null) {INSTANCE = Room.databaseBuilder(context, AppDataBase.class, DATA_BASE_NAME).build();}}}return INSTANCE;}
}