Android: Basic usage of Room database—Simple application_1_Getting started

1.Room introduction:

Android Room is a persistence library officially provided by Android for managing databases in Android applications. It provides a simple API layer that makes working with SQLite databases easier and more convenient.

Here are the main features of Android Room:

1. Object-relational mapping (ORM): Room allows you to map Java or Kotlin objects into database tables. You can define a data model and use annotations to define relationships and constraints.
2. Transaction management: Room provides transaction management functions to ensure data integrity and consistency. It also supports automatic commit and rollback mechanisms, similar to transaction management in JDBC.
3. Database abstraction: Room provides an abstraction layer that allows you to use a simple API to perform SQL queries and operate the database. Instead of writing manual SQL statements, you use Java or Kotlin's query API.
4. Synchronous and asynchronous operations: Room supports synchronous and asynchronous operations, making it easy to perform database operations in a background thread to avoid blocking the main thread.
5. Database migration: When your application is updated, it may be necessary to change the database schema. Room can automatically handle the migration process, ensuring data consistency and integrity.
6. Concurrency support: Room supports multi-threaded concurrent operations and can effectively handle multiple concurrent requests.
7. Embedded databases: Room supports embedded databases, which means you can embed database files into your application without having to separately install and manage a SQLite database.
8. Cross-platform support: In addition to the Android platform, Room also supports iOS and desktop applications.

In summary, Android Room is a powerful persistence library that makes managing SQLite databases easier and more convenient. It provides an object-relational mapping layer, transaction management, database abstraction, and more to help you more easily build and manage databases in Android applications.

2.Room usage:

Tutorial: Room | Jetpack | Android Developers

Development documents:androidx.room | Android Developers

1. Import dependencies: Add it to the build.gradle file

dependencies {

        //Room
        def room_version = "2.5.0"
        implementation "androidx.room:room-runtime:$room_version"
        annotationProcessor "androidx.room:room-compiler:$room_version"
}

2. Create the entity class People.java

package com.example.myroom.entity;

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;

//实体类 表名 不写默认内名首字母小写 people
@Entity(tableName = "people")
public class People {
    //主键 自动生成
    @PrimaryKey(autoGenerate = true)
    private int id;

    //列的名称
    @ColumnInfo(name = "user_name")
    private String name;

    //不写默认列的名称为age，sex
    private int age;
    private String sex;

    public People(String name, int age, String sex) {
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getId() {
        return 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 String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }
}

3. Create an interface Dao PeopleDao.java

package com.example.myroom.dao;

import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
import androidx.room.Update;

import com.example.myroom.entity.People;

import java.util.List;

//dao database access object 接口 处理数据库的方法签名
@Dao
public interface PeopleDao {

    //添加  传递一个参数 对象
    @Insert
    void insertDataOne(People people);

    //添加  可以传递多个参数 对象
    @Insert
    void insertDataS(People... people);

    //删除
    @Delete
    int deleteDataS(People... people);

    //修改 传入对象 设置 id 进行修改某一个
    @Update
    int updateData(People... people);

    //查询 根据id倒序
    @Query("select * from people order by id desc")
    List<People> getPeoples();

    //根据id查询
    @Query("select * from people where id =:numb")
    People getPeople(Integer numb);

    //删除表数据
    @Query("delete from people")
    void deleteTableData();

}

4. Write an abstract class that inherits RoodDatabase

package com.example.myroom.dao;

import androidx.room.Database;
import androidx.room.RoomDatabase;

import com.example.myroom.entity.People;

//抽象类 继承 RoomDatabase      我们不用实现people中的方法
// version = 1 数据库版本，exportSchema = false不允许导出数据库的架构
@Database(entities = {People.class}, version = 1, exportSchema = false)
public abstract class PeopleDataBase extends RoomDatabase {
    /**
     * Java 抽象类的一些特点
     * 不能被实例化：抽象类不能被实例化，因为它没有具体的实现细节。它只能被继承，并且子类必须实现抽象类中的所有抽象方法。
     * 包含抽象方法：抽象类可以包含抽象方法，这些方法只有声明但没有实现。子类必须实现这些抽象方法，否则它也必须被声明为抽象类。
     * 提供通用功能和行为：抽象类提供了一些通用功能和行为，这些功能和行为可以被其子类继承和重用。子类可以根据需要扩展这些功能和行为，或者重写它们以提供不同的实现。
     * 用于设计高层次的抽象：抽象类可以用于表示一个高层次的抽象概念或者一个通用模板，使得代码更加模块化和可维护。通过将一些公共方法和行为提取到一个抽象类中，可以避免在多个子类中重复实现相同的功能。
     * 扩展性：抽象类可以定义一些扩展的接口，子类可以选择实现这些接口来提供额外的功能。这使得抽象类具有很好的扩展性，可以根据需要添加新的功能和行为
     */

/*

    public abstract PeopleDao peopleDao();


}

4.MainActivity.java

package com.example.myroom;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;
import androidx.room.Room;

import com.example.myroom.dao.PeopleDao;
import com.example.myroom.dao.PeopleDataBase;
import com.example.myroom.entity.People;

import java.util.List;

public class MainActivity extends AppCompatActivity {

    PeopleDataBase DB;
    private Button btnInsert, btnDelete, btnUpdate, btnSelect, btnDeleteData;
    private TextView textContent;
    private EditText etName, etAge, etSex, etSelect, etDelete, etUpdate;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        DB = Room.databaseBuilder(this, PeopleDataBase.class, "peopleDB")
                // 默认不允许在主线程中连接数据库   强制在主线程中处理
                .allowMainThreadQueries()
                .build();
        textContent = findViewById(R.id.tvcontent);
        etName = findViewById(R.id.etName);
        etAge = findViewById(R.id.etAge);
        etSex = findViewById(R.id.etSex);
        etSelect = findViewById(R.id.etSelect);
        etDelete = findViewById(R.id.etDelete);
        etUpdate = findViewById(R.id.etUpdate);

        btnInsert = findViewById(R.id.btnSave);
        btnDelete = findViewById(R.id.btnDelete);
        btnUpdate = findViewById(R.id.btnUpdate);
        btnSelect = findViewById(R.id.btnselect);
        btnDeleteData = findViewById(R.id.btnDeleteTB);

        //查询数据
        selectData(null);

        //按钮事件 插入数据
        btnInsert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //插入数据 防止空
                String name = etName.getText().toString().equals("") ? "张三" : etName.getText().toString();
                int age = etAge.getText().toString().equals("") ? 20 : Integer.parseInt(etAge.getText().toString());
                String sex = etSex.getText().toString().equals("") ? "男" : etSex.getText().toString();
                People people = new People(name, age, sex);
                DB.peopleDao().insertDataS(people);
                //查询数据
                selectData(null);

            }
        });

        //修改数据
        btnUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //修改
                int id = etUpdate.getText().toString().equals("") ? 0 : Integer.parseInt(etUpdate.getText().toString());
                if (id != 0) {
                    String name = etName.getText().toString();
                    int age = Integer.parseInt(etAge.getText().toString());
                    String sex = etSex.getText().toString();
                    People people = new People(name, age, sex);
                    people.setId(id);
                    DB.peopleDao().updateData(people);
                    //查询
                    selectData(null);
                }

            }
        });

        //删除
        btnDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int id = etDelete.getText().toString().equals("") ? 0 : Integer.parseInt(etDelete.getText().toString());
                if (id != 0) {
                    People people = new People();
                    people.setId(id);
                    DB.peopleDao().deleteDataS(people);
                    //查询
                    selectData(null);
                }

            }
        });

        //根据id 查数据
        btnSelect.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int id = etSelect.getText().toString().equals("") ? 0 : Integer.parseInt(etSelect.getText().toString());
                if (id != 0) {
                    selectData(id);
                }

            }
        });

        //删除全部数据
        btnDeleteData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                DB.peopleDao().deleteTableData();
            }
        });

    }

    /**
     * 查询数据的方法
     */
    public void selectData(Integer id) {
        try {
            StringBuilder text = new StringBuilder();
            if (id == null || id == 0) {
                List<People> peopleList = DB.peopleDao().getPeoples();
                if (peopleList.size() != 0) {
                    for (int i = 0; i < peopleList.size(); i++) {
                        People people = peopleList.get(i);
                        text.append("id:")
                                .append(people.getId())
                                .append("---name:")
                                .append(people.getName())
                                .append("---age:")
                                .append(people.getAge())
                                .append("---sex:")
                                .append(people.getSex())
                                .append("\n");
                    }
                } else {
                    text.append("没有可用的数据");
                }

            } else {
                People people = DB.peopleDao().getPeople(id);
                text.append("id:")
                        .append(people.getId())
                        .append("---name:")
                        .append(people.getName())
                        .append("---age:")
                        .append(people.getAge())
                        .append("---sex:")
                        .append(people.getSex());
            }

            textContent.setText(text.toString());

        } catch (Exception e) {
            Log.e("TAG", "----查询失败------------" + e.getMessage());
        }


    }

}

5. Layout file activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btnUpdate"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="修改"
        app:layout_constraintBottom_toBottomOf="@+id/etUpdate"
        app:layout_constraintEnd_toStartOf="@+id/guideline10"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/etUpdate"
        app:layout_constraintTop_toTopOf="@+id/etUpdate"
        app:layout_constraintVertical_bias="0.0" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.05" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:text="Room简单应用："
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@+id/guideline2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btnSave"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="4dp"
        android:text="保存"
        app:layout_constraintBottom_toTopOf="@+id/guideline9"
        app:layout_constraintEnd_toStartOf="@+id/guideline10"
        app:layout_constraintHorizontal_bias="0.203"
        app:layout_constraintStart_toStartOf="@+id/guideline5"
        app:layout_constraintTop_toTopOf="@+id/guideline4" />

    <Button
        android:id="@+id/btnDelete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="删除"
        app:layout_constraintBottom_toBottomOf="@+id/etDelete"
        app:layout_constraintEnd_toStartOf="@+id/guideline10"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/etDelete"
        app:layout_constraintTop_toTopOf="@+id/etDelete" />

    <Button
        android:id="@+id/btnselect"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="查询"
        app:layout_constraintBottom_toBottomOf="@+id/etSelect"
        app:layout_constraintEnd_toStartOf="@+id/guideline10"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/etSelect"
        app:layout_constraintTop_toTopOf="@+id/etSelect" />

    <Button
        android:id="@+id/btnDeleteTB"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="4dp"
        android:text="删除表数据"
        app:layout_constraintBottom_toTopOf="@+id/guideline9"
        app:layout_constraintEnd_toStartOf="@+id/guideline10"
        app:layout_constraintHorizontal_bias="0.873"
        app:layout_constraintStart_toStartOf="@+id/guideline5"
        app:layout_constraintTop_toTopOf="@+id/guideline4" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.13" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.29548565" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="姓名："
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@+id/guideline3"
        app:layout_constraintEnd_toStartOf="@+id/etName"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="@+id/guideline5" />

    <EditText
        android:id="@+id/etName"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="请输入"
        android:inputType="text"
        app:layout_constraintBottom_toBottomOf="@+id/textView2"
        app:layout_constraintEnd_toStartOf="@+id/guideline10"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/textView2"
        app:layout_constraintTop_toTopOf="@+id/textView2" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline5"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.05352798" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline6"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.21" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline8"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.6" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline9"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.37" />

    <TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="性别："
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@+id/guideline6"
        app:layout_constraintEnd_toStartOf="@+id/etSex"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="@+id/guideline5" />

    <EditText
        android:id="@+id/etSex"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="请输入"
        android:inputType="text"
        app:layout_constraintBottom_toBottomOf="@+id/textView3"
        app:layout_constraintEnd_toStartOf="@+id/guideline10"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/textView3"
        app:layout_constraintTop_toTopOf="@+id/textView3" />

    <EditText
        android:id="@+id/etAge"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="请输入"
        android:inputType="number"
        app:layout_constraintBottom_toBottomOf="@+id/textView4"
        app:layout_constraintEnd_toStartOf="@+id/guideline10"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/textView4"
        app:layout_constraintTop_toTopOf="@+id/textView4" />

    <TextView
        android:id="@+id/textView4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="年龄："
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@+id/guideline4"
        app:layout_constraintEnd_toStartOf="@+id/etAge"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="@+id/guideline5" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline10"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.9" />

    <EditText
        android:id="@+id/etSelect"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="请输入id"
        android:inputType="number"
        app:layout_constraintBottom_toTopOf="@+id/guideline8"
        app:layout_constraintEnd_toStartOf="@+id/btnselect"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="@+id/guideline5"
        app:layout_constraintTop_toTopOf="@+id/guideline9"
        app:layout_constraintVertical_bias="0.0" />

    <EditText
        android:id="@+id/etDelete"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="请输入id"
        android:inputType="number"
        app:layout_constraintBottom_toTopOf="@+id/guideline8"
        app:layout_constraintEnd_toStartOf="@+id/btnDelete"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="@+id/guideline5"
        app:layout_constraintTop_toTopOf="@+id/guideline9"
        app:layout_constraintVertical_bias="0.451" />

    <EditText
        android:id="@+id/etUpdate"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="请输入id"
        android:inputType="number"
        app:layout_constraintBottom_toTopOf="@+id/guideline8"
        app:layout_constraintEnd_toStartOf="@+id/btnUpdate"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="@+id/guideline5"
        app:layout_constraintTop_toTopOf="@+id/etSelect"
        app:layout_constraintVertical_bias="1.0" />

    <TextView
        android:id="@+id/tvcontent"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/guideline10"
        app:layout_constraintStart_toStartOf="@+id/guideline5"
        app:layout_constraintTop_toTopOf="@+id/guideline8"
        tools:hint="这里显示数据" />

</androidx.constraintlayout.widget.ConstraintLayout>

sample graph:

database:

Export these three files to view the database: