最近在kotlin環境下，寫了一個room資料庫的demo，各種情況跑了一下，在此總結一下。
涉及情況：增、删、改、查、排序
1、環境搭建
1.1、Android Studio下，建立一個kotlin項目，
1.2、去app的build.gradle中進行一些配置
頂部增加
apply plugin: 'kotlin-kapt'
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然後
defaultConfig {
......
javaCompileOptions {
annotationProcessorOptions {
arguments = ["room.schemaLocation":
"$projectDir/schemas".toString()]
}
}
}
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1.3、導入依賴
implementation 'android.arch.persistence.room:runtime:1.1.1'
kapt 'android.arch.persistence.room:compiler:1.1.1'
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2、建立一個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
}
}
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3、分别建立Student和Teacher（我寫了2張表）
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?
)
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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?,
//教學年限
@ColumnInfo(name = "t_year")
var teachYear: Int?
)
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4、與之對應的，分别建立StudentDao和TeacherDao
import android.arch.persistence.room.*
@Dao
interface BaseDao<T> {
@Insert(onConflict = OnConflictStrategy.REPLACE)
fun insertAll(list: MutableList<T>)
@Delete
fun delete(element: T)
@Delete
fun deleteList(elements:MutableList<T>)
@Delete
fun deleteSome(vararg elements:T)
@Update
fun update(element: T)
}
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import android.arch.persistence.room.*
@Dao
interface StudentDao:BaseDao<Student> {
@Insert(onConflict = OnConflictStrategy.REPLACE)
fun insert(element:Student)
@Query("select * from Student")
fun getAllStudents():MutableList<Student>
@Query("select * from Student where studentID = :studentID")
fun getStudnet(studentID:Int):Student
@Query("select * from Student order by studentID desc ")
fun getAllByDateDesc():MutableList<Student>
@Query("delete from Student")
fun deleteAll()
}
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import android.arch.persistence.room.*
@Dao
interface TeacherDao:BaseDao<Teacher> {
@Insert
fun insert(element:Teacher)
@Query("select * from Teacher")
fun getAllTeachers():MutableList<Teacher>
@Query("select * from Teacher where teacherID = :teacherID")
fun getTeacher(teacherID:Int):Teacher
@Query("select * from Teacher order by t_year desc ")
fun getAllByDateDesc():MutableList<Teacher>
@Query("delete from Teacher")
fun deleteAll()
}
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這裡，注意下StudentDao和TeacherDao中，insert上面的注解，有差別，後面會說到
5、接下來，建立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()
}
}
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這裡，我用的是 靜态内部類 的單例，還可以寫作
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!!
}
}
}
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這裡，不做讨論，kotlin的單例，也有多種寫法。
到此為止，準備工作，都做完了。開始實際的使用：
Activity中：
val sDao: StudentDao = AppDataBase.instance.getStudentDao()
var s_1 = Student(1, "s1", "國小")
var s_2 = Student(2, "s2", "國小")
var s_3 = Student(3, "s3", "國小")
var s_6 = Student(6, "s6", "大學")
var s_5 = Student(5, "s5", "大學")
var s_4 = Student(4, "s4", "大學")
var sList: MutableList<Student> = mutableListOf<Student>()
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傳進去，也可以一個一個單獨添加
sDao.insertAll(sList)
var sList_select_1: MutableList<Student> = sDao.getAllStudents()
for (i in sList_select_1.indices) {
println(sList_select_1.get(i))
}
日志：
Student(studentID=1, studentName=s1, studentType=國小)
Student(studentID=2, studentName=s2, studentType=國小)
Student(studentID=3, studentName=s3, studentType=國小)
Student(studentID=4, studentName=s4, studentType=大學)
Student(studentID=5, studentName=s5, studentType=大學)
Student(studentID=6, studentName=s6, studentType=大學)
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插入，查詢成功，接下來，對資料進行修改：
//注意，這裡我用的是insert，而不是 update
sDao.insert(Student(1, "s1", "大學"))
var sList_select_2: MutableList<Student> = sDao.getAllStudents()
for (i in sList_select_2.indices) {
println(sList_select_2.get(i))
}
日志：
Student(studentID=1, studentName=s1, studentType=大學)//這條資料變了
Student(studentID=2, studentName=s2, studentType=國小)
Student(studentID=3, studentName=s3, studentType=國小)
Student(studentID=4, studentName=s4, studentType=大學)
Student(studentID=5, studentName=s5, studentType=大學)
Student(studentID=6, studentName=s6, studentType=大學)
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接下來，對資料進行删除試試
sDao.deleteSome(Student(100, "s100", "高中"), s_6)
var sList_select_3: MutableList<Student> = sDao.getAllStudents()
for (i in sList_select_3.indices) {
println(sList_select_3.get(i))
}
日志：
Student(studentID = 1, studentName = s1, studentType = 大學)
Student(studentID = 2, studentName = s2, studentType = 國小)
Student(studentID = 3, studentName = s3, studentType = 國小)
Student(studentID = 4, studentName = s4, studentType = 大學)
Student(studentID = 5, studentName = s5, studentType = 大學)
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從删除可以看出，删除不存在的Student資料，不會報錯，隻是沒有效果，删除存在的資料，就是正常删除
接下來，對Teacher表進行一些操作
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<Teacher> = mutableListOf<Teacher>()
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<Teacher> = 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)
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對教師資料進行排序（按照教學年限）
var tList_select_2: MutableList<Teacher> = 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)
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現在，要對 ID=1 的老師做修改，把他的教學年限，改成11，還是用之前Student的那種寫法：
tDao.insert(Teacher(1,"t1",11))
報錯：
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)
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到這來，應該知道，insert上面那句注解
@Insert(onConflict = OnConflictStrategy.REPLACE)
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的含義和作用了吧！
如果沒有這個注解，插入已有資料，會報錯！如果有這個注解，插入以後資料，僅僅是替換。
因為Teacher沒有加這個注解，用update試試
tDao.update(Teacher(1, "t1", 11))
var tList_select_3: MutableList<Teacher> = 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)
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版權聲明：本文為CSDN部落客「夜盡天明89」的原創文章，遵循CC 4.0 BY-SA版權協定，轉載請附上原文出處連結及本聲明。
原文連結：https://blog.csdn.net/u014620028/article/details/90719716
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