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Jetpack学习-5-Room

Jetpack学习-5-Room

作者: 主音King | 来源:发表于2020-08-17 09:15 被阅读0次

    Room是什么

    持久性库在SQLite基础上提供抽象层,充分利用SQLite强大功能,更强的数据库访问机制。
    Room是基于SQLite封装的一个框架。

    简单使用

    引入room,模块build.gradle增加配置

    dependencies {
       ...
        implementation 'androidx.room:room-runtime:2.2.5'
        annotationProcessor 'androidx.room:room-compiler:2.2.5'
    }
    

    Entity

    // @Entity 标识这个类用于建表,表名(默认不写,则用类名小写作为表名)
    @Entity(tableName = "student")
    public class Student {
        // 主键,是否自增长
        @PrimaryKey(autoGenerate = true)
        public int id;
        // 表中字段,表中字段名
        @ColumnInfo(name = "name")
        public String name;
        // 表中字段,默认使用下面字段名age
        @ColumnInfo
        public int age;
    
        @Override
        public String toString() {
            return "Student{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }
    

    Dao

    @Dao
    public interface StudentDao {
        @Insert(onConflict = OnConflictStrategy.REPLACE)
        void insert(Student... students);
    
        @Delete
        void delete(Student student);
    
        @Update
        void update(Student student);
    
        @Query("SELECT * FROM student")
        List<Student> getAll();
    
        @Query("SELECT * FROM student WHERE name = :name")
        List<Student> findByName(String name);
    
        @Query("SELECT * FROM student WHERE id in (:ids)")
        List<Student> findByIds(int[] ids);
    }
    

    DataBase

    @Database(entities = {Student.class},version = 1)
    public abstract class DataBase extends RoomDatabase {
        public abstract StudentDao studentDao();
    }
    

    使用

    public class RoomActivity extends AppCompatActivity {
        private static final String TAG = "Room-";
        private StudentDao dao;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_room);
            DataBase dataBase = Room.databaseBuilder(getApplicationContext(), DataBase.class,
                    "room").allowMainThreadQueries().build();
            dao = dataBase.studentDao();
            String[] permissions = {Manifest.permission.WRITE_EXTERNAL_STORAGE};
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                requestPermissions(permissions, 1);
            }
        }
    
        @Override
        public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
            if (requestCode == 1) {
                Log.d(TAG, "onRequestPermissionsResult: " + requestCode);
                for (int i = 0; i < grantResults.length; i++) {
                    if (grantResults[i] != PackageManager.PERMISSION_GRANTED) {
                        Log.d(TAG, "onRequestPermissionsResult-需要开启存储权限");
                    }
                }
            }
            super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        }
    
        /**
         * 在Activity中所有对数据库的操作(增、删、改、查)都不可以在主线程中进行,除非在数据库的Builder上调用了allowMainThreadQueries(),
         * 或者所有的操作都在子线程中完成,否则程序会崩溃报以下错误
         * Cannot access database on the main thread since it may potentially lock the UI for a long period of time.
         *
         * @param view
         */
        public void queryAll(View view) {
            List<Student> students = dao.getAll();
            Log.d(TAG, "queryAll: " + students);
        }
    
        public void insert(View view) {
            Student student = new Student();
            student.age = 18;
            student.name = "小明";
            dao.insert(student);
            Log.d(TAG, "insert:" + student.toString());
        }
    
        /**
         * 删除必须指定id,否则删除不成功(id不存在也是删除不成功的)
         *
         * @param view
         */
        public void delete(View view) {
            Student student = new Student();
            student.age = 18;
            student.name = "小明";
            student.id = 1;
            dao.delete(student);
            Log.d(TAG, "insert:" + student.toString());
        }
    
        /**
         * 更新必须指定id,否则不成功(id不存在也是更新不成功的)
         *
         * @param view
         */
        public void update(View view) {
            Student student = new Student();
            student.age = 18;
            student.name = "小明-1";
            student.id = 1;
            dao.update(student);
            Log.d(TAG, "insert:" + student.toString());
        }
    
        public void queryByName(View view) {
            Log.d(TAG, "queryByName: " + dao.findByName("小明"));
        }
    
        public void queryByIds(View view) {
            Log.d(TAG, "queryByName: " + dao.findByIds(new int[]{1, 2, 3}));
        }
    }
    

    当然这是基础用法,有关数据库升级、多表关联、查询部分字段等随后写。

    数据库信息导出

    允许表信息导出json文件。应该在版本控制中保存该文件,代表数据库历史,允许创建就版本数据库用于测试。配置如下build.gradle

    android{
        defaultConfig {
            ···
            javaCompileOptions {
                annotationProcessorOptions {
                    arguments = ["room.schemaLocation":
                                         "$projectDir/schemas".toString()]
                }
            }
        }
        // 用于测试
        sourceSets {
            androidTest.assets.srcDirs += files("$projectDir/schemas".toString())
        }
    }
    

    schemas路径:项目名/app/schemas


    image.png
    {
      "formatVersion": 1,
      "database": {
        "version": 1,
        "identityHash": "acca4b709e6c8b9b88d8328be36b9032",
        "entities": [
          {
            "tableName": "student",
            "createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `name` TEXT, `age` INTEGER NOT NULL)",
            "fields": [
              {
                "fieldPath": "id",
                "columnName": "id",
                "affinity": "INTEGER",
                "notNull": true
              },
              {
                "fieldPath": "name",
                "columnName": "name",
                "affinity": "TEXT",
                "notNull": false
              },
              {
                "fieldPath": "age",
                "columnName": "age",
                "affinity": "INTEGER",
                "notNull": true
              }
            ],
            "primaryKey": {
              "columnNames": [
                "id"
              ],
              "autoGenerate": true
            },
            "indices": [],
            "foreignKeys": []
          }
        ],
        "views": [],
        "setupQueries": [
          "CREATE TABLE IF NOT EXISTS room_master_table (id INTEGER PRIMARY KEY,identity_hash TEXT)",
          "INSERT OR REPLACE INTO room_master_table (id,identity_hash) VALUES(42, 'acca4b709e6c8b9b88d8328be36b9032')"
        ]
      }
    }
    

    原理

    大量用了注解,Room是根据注解处理器辅助生成类文件。

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