Android jetpack room SQLLite 数据库 修改字段

Posted 2022-05-23 安果移不动

由于sqlLite 修改字段比较复杂。所以建议销毁、复制数据。然后重建数据

将Sex 字段由Int转换为String 

修改数据bean

package com.anguomob.jecpack.bean

import androidx.room.ColumnInfo
import androidx.room.Entity
import androidx.room.Ignore
import androidx.room.PrimaryKey

@Entity(tableName = "student")
data class Student(
    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "id", typeAffinity = ColumnInfo.INTEGER)
    var id: Int,
    @ColumnInfo(name = "name", typeAffinity = ColumnInfo.TEXT)
    var name: String,
    @ColumnInfo(name = "age", typeAffinity = ColumnInfo.INTEGER)
    var age: Int,
    /**
     * V3
     */
//    @ColumnInfo(name = "sex", typeAffinity = ColumnInfo.INTEGER)
//    var sex: Int,
    /**
     * V4
     */
    @ColumnInfo(name = "sex", typeAffinity = ColumnInfo.TEXT)
    var sex: String,
    @ColumnInfo(name = "bar_data", typeAffinity = ColumnInfo.INTEGER)
    var bar_data: Int
) 

    @Ignore
    constructor(name: String, age: Int) : this(0, name, age, "M", 1)


    @Ignore
    constructor(id: Int) : this(id, "", 0, "M", 1)

具体操作

package com.anguomob.jecpack.database

import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
import androidx.room.migration.Migration
import androidx.sqlite.db.SupportSQLiteDatabase
import com.anguomob.jecpack.bean.Student
import com.anguomob.jecpack.dao.StudentDao
import okhttp3.internal.Internal.instance

@Database(entities = [Student::class], version = 4, exportSchema = true)
abstract class MyDataBase : RoomDatabase() 
    companion object 
        var DATABASE_NAME = "my_db.db"
        private lateinit var instance: MyDataBase

        //数据库从1 到2 版本的升级
        var MIGATION_1_2: Migration = object : Migration(1, 2) 
            override fun migrate(database: SupportSQLiteDatabase) 
                //新增性别
                database.execSQL("ALTER TABLE student ADD COLUMN sex INTEGER NOT NULL DEFAULT 1")
            
        

        var MIGATION_2_3: Migration = object : Migration(2, 3) 
            override fun migrate(database: SupportSQLiteDatabase) 
                //新增性别
                database.execSQL("ALTER TABLE student ADD COLUMN `bar_data` INTEGER NOT NULL DEFAULT 1")
            
        


        var MIGATION_3_4: Migration = object : Migration(3, 4) 
            override fun migrate(database: SupportSQLiteDatabase) 
                //修改性别字段为Text
                // 1、 创建临时表
                database.execSQL(
                    "CREATE TABLE `temp_student` ("
                            + "`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "
                            + "`name` TEXT NOT NULL, "
                            + "`age` INTEGER NOT NULL, "
                            + "`sex` TEXT NOT NULL DEFAULT 'M',"
                            + " `bar_data` INTEGER NOT NULL"
                            + ")"
                )

                //2 复制数据
                database.execSQL(
                    "INSERT INTO `temp_student` (name,age,sex,bar_data)"
                            + "SELECT name,age,sex,bar_data FROM student"
                )


                //3 删除原来表
                database.execSQL("DROP TABLE STUDENT")
                //4 重命名
                database.execSQL("ALTER TABLE temp_student RENAME TO student")
                //修改原来的表的数据为正常数据
                database.execSQL(
                    "update student set sex = 'M' where sex = '1'"
                )

                database.execSQL(
                    "update student set sex = 'F' where sex = '2'"
                )

            
        


        fun getSingle(context: Context): MyDataBase 
            if (::instance.isInitialized.not()) 
                instance = Room.databaseBuilder(
                    context.applicationContext,
                    MyDataBase::class.java,
                    DATABASE_NAME
                )
//                    .allowMainThreadQueries()//允许主线程操作数据库
                    .addMigrations(MIGATION_1_2, MIGATION_2_3, MIGATION_3_4)
                    //出现异常问题 重建数据表，同时数据也会丢失。
                    .fallbackToDestructiveMigration()
                    .build();
            

            return instance;
        


    


    abstract fun getStudentDao(): StudentDao

 重点关注代码 MIGATION_3_4里面的sql语句