Android Room By Kotlin

た入场券 2022-08-31 13:19 216阅读 0赞

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'  
1  
然后

defaultConfig \{  
......  
javaCompileOptions \{  
annotationProcessorOptions \{  
arguments = \["room.schemaLocation":  
"$projectDir/schemas".toString()\]  
\}  
\}  
\}  
1  
2  
3  
4  
5  
6  
7  
8  
9  
1.3、导入依赖

implementation 'android.arch.persistence.room:runtime:1.1.1'  
kapt 'android.arch.persistence.room:compiler:1.1.1'  
1  
2  
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  
\}

\}  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
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?

)  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
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?

)  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
4、与之对应的，分别创建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)

\}  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
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()

\}  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
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()

\}  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
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()  
\}

\}  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
22  
23  
24  
25  
26  
27  
28  
29  
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!!  
\}

\}  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
22  
23  
24  
25  
26  
27  
28  
29  
30  
31  
32  
33  
34  
35  
36  
37  
38  
39  
40  
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<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传进去，也可以一个一个单独添加  
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=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)  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
22  
23  
24  
25  
26  
27  
28  
29  
30  
31  
32  
33  
34  
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<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)  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
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<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)  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
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<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)  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
22  
23  
24  
25  
26  
27  
28  
29  
对教师数据进行排序（按照教学年限）

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)  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
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)  
1  
2  
3  
4  
5  
6  
7  
到这来，应该知道，insert上面那句注解

@Insert(onConflict = OnConflictStrategy.REPLACE)  
1  
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<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)  
————————————————  
版权声明：本文为CSDN博主「夜尽天明89」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。  
原文链接：https://blog.csdn.net/u014620028/article/details/90719716