kotlin中使用Room数据库

最近在kotlin环境下，写了一个room数据库的demo，各种情况跑了一下，在此总结一下。

涉及情况：增、删、改、查、排序

1、环境搭建
1.1、Android Studio下，新建一个kotlin项目，
1.2、去app的build.gradle中进行一些配置
顶部增加

apply plugin: 'kotlin-kapt'

然后

defaultConfig {
        ......
        javaCompileOptions {
            annotationProcessorOptions {
                arguments = ["room.schemaLocation":
                                     "$projectDir/schemas".toString()]
            }
        }
}

1.3、导入依赖

implementation 'android.arch.persistence.room:runtime:1.1.1'
kapt 'android.arch.persistence.room:compiler:1.1.1'

2、创建一个Application，用于提供全局上下文

class MyApplication : Application() {

    companion object {

        var instance: MyApplication by Delegates.notNull()

        fun instance() = instance
    }

    override fun onCreate() {
        super.onCreate()

        instance = this
    }

}

3、分别创建Student和Teacher（我写了2张表）

import android.arch.persistence.room.ColumnInfo
import android.arch.persistence.room.Entity
import android.arch.persistence.room.PrimaryKey

@Entity(tableName = "Student")
data class Student(

    @PrimaryKey(autoGenerate = true)
    var studentID: Int?,
    @ColumnInfo(name = "s_name")
    var studentName: String?,
    @ColumnInfo(name = "s_type")
    var studentType: String?

)

import android.arch.persistence.room.ColumnInfo
import android.arch.persistence.room.Entity
import android.arch.persistence.room.PrimaryKey

@Entity(tableName = "Teacher")
data class Teacher(

    @PrimaryKey(autoGenerate = true)
    var teacherID: Int?,
    @ColumnInfo(name = "t_name")
    var teacherName: String?,
    //教学年限
    @ColumnInfo(name = "t_year")
    var teachYear: Int?

)

4、与之对应的，分别创建StudentDao和TeacherDao

import android.arch.persistence.room.*

@Dao
interface BaseDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insertAll(list: MutableList)

    @Delete
    fun delete(element: T)

    @Delete
    fun deleteList(elements:MutableList)

    @Delete
    fun deleteSome(vararg elements:T)

    @Update
    fun update(element: T)

}

import android.arch.persistence.room.*

@Dao
interface StudentDao:BaseDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insert(element:Student)

    @Query("select * from Student")
    fun getAllStudents():MutableList

    @Query("select * from Student where studentID = :studentID")
    fun getStudnet(studentID:Int):Student

    @Query("select * from Student order by studentID desc ")
    fun getAllByDateDesc():MutableList

    @Query("delete from Student")
    fun deleteAll()

}

import android.arch.persistence.room.*

@Dao
interface TeacherDao:BaseDao {

    @Insert
    fun insert(element:Teacher)

    @Query("select * from Teacher")
    fun getAllTeachers():MutableList

    @Query("select * from Teacher where teacherID = :teacherID")
    fun getTeacher(teacherID:Int):Teacher

    @Query("select * from Teacher order by t_year desc ")
    fun getAllByDateDesc():MutableList

    @Query("delete from Teacher")
    fun deleteAll()

}

这里，注意下StudentDao和TeacherDao中，insert上面的注解，有区别，后面会说到

5、接下来，创建AppDataBase

import android.arch.persistence.room.Database
import android.arch.persistence.room.RoomDatabase
import android.arch.persistence.room.Room

@Database(entities = [Student::class, Teacher::class], version = 1)
abstract class AppDataBase : RoomDatabase() {

    abstract fun getStudentDao(): StudentDao

    abstract fun getTeacherDao(): TeacherDao

    companion object {

        val instance = Single.sin

    }

    private object Single {

        val sin :AppDataBase= Room.databaseBuilder(
            MyApplication.instance(),
            AppDataBase::class.java,
            "User.db"
        )
            .allowMainThreadQueries()
            .build()
    }

}

这里，我用的是 静态内部类 的单例，还可以写作

import android.arch.persistence.room.Database
import android.arch.persistence.room.RoomDatabase
import android.arch.persistence.room.Room

@Database(entities = [Student::class, Teacher::class], version = 1)
abstract class AppDataBase : RoomDatabase() {

    abstract fun getStudentDao(): StudentDao

    abstract fun getTeacherDao(): TeacherDao

    companion object {

        @Volatile
        private var instance: AppDataBase? = null

        fun getDBInstace(): AppDataBase {

            if (instance == null) {

                synchronized(AppDataBase::class) {

                    if (instance == null) {

                        instance = Room.databaseBuilder(
                            MyApplication.instance(),
                            AppDataBase::class.java,
                            "User.db"
                        )
                            .allowMainThreadQueries()
                            .build()
                    }
                }
            }
            return instance!!
        }

    }

}

这里，不做讨论，kotlin的单例，也有多种写法。

到此为止，准备工作，都做完了。开始实际的使用：
Activity中：

val sDao: StudentDao = AppDataBase.instance.getStudentDao()

var s_1 = Student(1, "s1", "小学")
var s_2 = Student(2, "s2", "小学")
var s_3 = Student(3, "s3", "小学")
var s_6 = Student(6, "s6", "大学")
var s_5 = Student(5, "s5", "大学")
var s_4 = Student(4, "s4", "大学")

var sList: MutableList = mutableListOf()

sList.add(s_1)
sList.add(s_2)
sList.add(s_3)
sList.add(s_6)
sList.add(s_5)
sList.add(s_4)

//可以直接把list传进去，也可以一个一个单独添加
sDao.insertAll(sList)

var sList_select_1: MutableList = sDao.getAllStudents()

for (i in sList_select_1.indices) {
	 println(sList_select_1.get(i))
}

日志：
	Student(studentID=1, studentName=s1, studentType=小学)
	Student(studentID=2, studentName=s2, studentType=小学)
	Student(studentID=3, studentName=s3, studentType=小学)
	Student(studentID=4, studentName=s4, studentType=大学)
	Student(studentID=5, studentName=s5, studentType=大学)
	Student(studentID=6, studentName=s6, studentType=大学)

插入，查询成功，接下来，对数据进行修改：

//注意，这里我用的是insert，而不是 update
sDao.insert(Student(1, "s1", "大学"))

var sList_select_2: MutableList = sDao.getAllStudents()

for (i in sList_select_2.indices) {
	println(sList_select_2.get(i))
}

日志：
Student(studentID=1, studentName=s1, studentType=大学)//这条数据变了
Student(studentID=2, studentName=s2, studentType=小学)
Student(studentID=3, studentName=s3, studentType=小学)
Student(studentID=4, studentName=s4, studentType=大学)
Student(studentID=5, studentName=s5, studentType=大学)
Student(studentID=6, studentName=s6, studentType=大学)

接下来，对数据进行删除试试

sDao.deleteSome(Student(100, "s100", "高中"), s_6)
var sList_select_3: MutableList = sDao.getAllStudents()

for (i in sList_select_3.indices) {
	println(sList_select_3.get(i))
}

日志：
Student(studentID = 1, studentName = s1, studentType = 大学)
Student(studentID = 2, studentName = s2, studentType = 小学)
Student(studentID = 3, studentName = s3, studentType = 小学)
Student(studentID = 4, studentName = s4, studentType = 大学)
Student(studentID = 5, studentName = s5, studentType = 大学)

从删除可以看出，删除不存在的Student数据，不会报错，只是没有效果，删除存在的数据，就是正常删除

接下来，对Teacher表进行一些操作

val tDao: TeacherDao = AppDataBase.instance.getTeacherDao()

var t_1 = Teacher(1, "t1", 10)
var t_2 = Teacher(2, "t2", 5)
var t_3 = Teacher(3, "t3", 3)
var t_4 = Teacher(4, "t4", 14)
var t_5 = Teacher(5, "t5", 22)

var tList: MutableList = mutableListOf()
tList.add(t_1)
tList.add(t_2)
tList.add(t_3)
tList.add(t_4)
tList.add(t_5)

tDao.insertAll(tList)

var tList_select_1: MutableList = tDao.getAllTeachers()

for (i in tList_select_1.indices) {
	println(tList_select_1.get(i))
}

日志：
Teacher(teacherID=1, teacherName=t1, teachYear=10)
Teacher(teacherID=2, teacherName=t2, teachYear=5)
Teacher(teacherID=3, teacherName=t3, teachYear=3)
Teacher(teacherID=4, teacherName=t4, teachYear=14)
Teacher(teacherID=5, teacherName=t5, teachYear=22)

对教师数据进行排序（按照教学年限）

var tList_select_2: MutableList = tDao.getAllByDateDesc()

for (i in tList_select_2.indices) {
	println(tList_select_2.get(i))
}

日志：
Teacher(teacherID=5, teacherName=t5, teachYear=22)
Teacher(teacherID=4, teacherName=t4, teachYear=14)
Teacher(teacherID=1, teacherName=t1, teachYear=10)
Teacher(teacherID=2, teacherName=t2, teachYear=5)
Teacher(teacherID=3, teacherName=t3, teachYear=3)

现在，要对 ID=1 的老师做修改，把他的教学年限，改成11，还是用之前Student的那种写法：

tDao.insert(Teacher(1,"t1",11))

报错：
Caused by: android.database.sqlite.SQLiteConstraintException:
	UNIQUE constraint failed: Teacher.teacherID 
	(Sqlite code 1555 SQLITE_CONSTRAINT_PRIMARYKEY),
	(OS error - 2:No such file or directory)

到这来，应该知道，insert上面那句注解

@Insert(onConflict = OnConflictStrategy.REPLACE)

的含义和作用了吧！

如果没有这个注解，插入已有数据，会报错！如果有这个注解，插入以后数据，仅仅是替换。

因为Teacher没有加这个注解，用update试试

tDao.update(Teacher(1, "t1", 11))

var tList_select_3: MutableList = tDao.getAllTeachers()

for (i in tList_select_3.indices) {
	println(tList_select_3.get(i))
}

日志：
Teacher(teacherID=1, teacherName=t1, teachYear=11)
Teacher(teacherID=2, teacherName=t2, teachYear=5)
Teacher(teacherID=3, teacherName=t3, teachYear=3)
Teacher(teacherID=4, teacherName=t4, teachYear=14)
Teacher(teacherID=5, teacherName=t5, teachYear=22)