学习过程记录
照着各种文章写，简单的实现都一样，可跑起来总是挂
java.lang.RuntimeException: cannot find implementation for com.charliesong.roomtest.room.JavaDatabase. JavaDatabase_Impl does not exist
at androidx.room.Room.getGeneratedImplementation(Room.java:94)
at androidx.room.RoomDatabase$Builder.build(RoomDatabase.java:723)
就是我们那个database类里获取实例Room.databaseBuilder（）.build()，调用build方法的时候就挂了。
提示很明显，这个database按道理系统应该自动生成一个Impl类的，可我们没有自动生成，可也不知道咋让他自动生成
public abstract class JavaDatabase extends RoomDatabase
各种解决都不行啊，不过好像和kotlin有关，最后我把room相关的类，都改成java写，然后就可以了。
如下
image.png
整理下基本操作
第一步app的build.gradle下添加库
def room_version = "1.1.1"
// or, for latest rc, use "1.1.1-rc1"
implementation "android.arch.persistence.room:runtime:$room_version"
// annotationProcessor "android.arch.persistence.room:compiler:$room_version"
kapt "android.arch.persistence.room:compiler:$room_version"
// optional - RxJava support for Room
implementation "android.arch.persistence.room:rxjava2:$room_version"
// optional - Guava support for Room, including Optional and ListenableFuture
implementation "android.arch.persistence.room:guava:$room_version"
// Test helpers
testImplementation "android.arch.persistence.room:testing:$room_version"
或者是androidx的
def room_version = "2.1.0-alpha02"
implementation "androidx.room:room-runtime:$room_version"
kapt "androidx.room:room-compiler:$room_version" // Kotlin 的话用kapt
// 如果需要用到 rxjava
implementation "androidx.room:room-rxjava2:$room_version"
// 如果需要用到 guava
implementation "androidx.room:room-guava:$room_version"
// 需要用到相关测试工具的话
testImplementation "androidx.room:room-testing:$room_version"
如果用kotlin的话，最上边应该是这样的
apply plugin: 'com.android.application'
apply plugin: 'kotlin-kapt'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
另外添加如下注释的地方下边的代码，具体可参考https://blog.csdn.net/hexingen/article/details/78725958
android {
compileSdkVersion 27
defaultConfig {
applicationId "com.charliesong.demo0327"
minSdkVersion 18
targetSdkVersion 27
versionCode 2
versionName "1.1"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
multiDexEnabled true
//指定room.schemaLocation生成的文件路径
javaCompileOptions {
annotationProcessorOptions {
arguments = ["room.schemaLocation": "$projectDir/schemas".toString()]
}
}
}
添加实体类
当一个类用@Entity注解并且被@Database注解中的entities属性所引用，Room就会在数据库中为那个entity创建一张表。
默认Room会为entity中定义的每一个field都创建一个column。如果一个entity中有你不想持久化的field，那么你可以使用@Ignore来注释它们
另外记得entity必须有一个@PrimaryKey 主键字段
import android.arch.persistence.room.ColumnInfo;
import android.arch.persistence.room.Entity;
import android.arch.persistence.room.PrimaryKey;
@Entity
public class Userjava {
@PrimaryKey(autoGenerate = true)
public int uid;
public String firstName;
public String lastName;
public int age;
@ColumnInfo(name = "region")//列的名字可以改
public String address;
}
添加数据访问对象dao
import android.arch.lifecycle.LiveData;
import android.arch.persistence.room.Dao;
import android.arch.persistence.room.Delete;
import android.arch.persistence.room.Insert;
import android.arch.persistence.room.Query;
import android.arch.persistence.room.Update;
import java.util.List;
@Dao
public interface UserJavaDao {
@Insert
void insertAll(Userjava... userjava);
@Query("select * from Userjava")
LiveData<List<Userjava>> getUsersFromSync();
@Delete
int delete(Userjava userjava);//参数可以是数组，集合，返回的是删除成功的条数
@Update
int update(Userjava... userjava);//参数可以是数组，集合，返回的是update成功的条数
}
database类
版本号必须>=1
import android.arch.persistence.db.SupportSQLiteDatabase;
import android.arch.persistence.room.Database;
import android.arch.persistence.room.Room;
import android.arch.persistence.room.RoomDatabase;
import android.arch.persistence.room.migration.Migration;
import android.support.annotation.NonNull;
import com.charliesong.demo0327.app.MyApplication;
@Database(entities = {Userjava.class},version =4)
public abstract class JavaDatabase extends RoomDatabase {
public abstract UserJavaDao userJavaDao();
private static JavaDatabase javaDatabase;
public static JavaDatabase instance(){
if(javaDatabase==null){
synchronized (JavaDatabase.class){
if(javaDatabase==null){
javaDatabase= Room.databaseBuilder(MyApplication.myApplication,JavaDatabase.class,"test").
addCallback(new Callback() {
@Override
public void onCreate(@NonNull SupportSQLiteDatabase db) {
super.onCreate(db);
System.out.println("onCreate==========="+db.getVersion()+"==="+db.getPath());
}
@Override
public void onOpen(@NonNull SupportSQLiteDatabase db) {
super.onOpen(db);
System.out.println("onOpen==========="+db.getVersion()+"==="+db.getPath());
}
})
.allowMainThreadQueries()//允许在主线程查询数据
.addMigrations(migration)//迁移数据库使用，下面会单独拿出来讲
.fallbackToDestructiveMigration()//迁移数据库如果发生错误，将会重新创建数据库，而不是发生崩溃
.build();
}
}
}
return javaDatabase;
}
//数据库升级用的
static Migration migration=new Migration(1,4) {
@Override
public void migrate(@NonNull SupportSQLiteDatabase database) {
System.out.println("migrate============"+database.getVersion());
database.execSQL("ALTER TABLE Userjava "+ " ADD COLUMN address TEXT");
}
};
}
然后就可以测试拉。
使用livedata比较方便，只处理数据库的增删改，发生变化livedata自动会变化，我们弄个observer就ok了，列表会自动刷新的
UtilRoomDB.getUserDao().usersFromSync.observe(this, Observer {
myAdapter.submitList(it)
})
我用的listAdapter
inner class MyAdapter(callback: DiffUtil.ItemCallback<Userjava>): ListAdapter<Userjava, BaseRvHolder>(callback)
顺道记录些其他问题
https://blog.csdn.net/hexingen/article/details/78725958
Error:(22, 17) 警告: Schema export directory is not provided to the annotation processor so we cannot export the schema.
You can either provide `room.schemaLocation` annotation processor argument OR set exportSchema to false.
方法1
@Database(entities = { YourEntity.class }, version = 1, exportSchema = false)
public abstract class MovieDatabase extends RoomDatabase {
...
}
方法2
android {
compileSdkVersion 26
buildToolsVersion "26.0.2"
defaultConfig {
applicationId "com.xingen.architecturecomponents"
minSdkVersion 15
targetSdkVersion 26
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
//指定room.schemaLocation生成的文件路径
javaCompileOptions {
annotationProcessorOptions {
arguments = ["room.schemaLocation": "$projectDir/schemas".toString()]
}
}
}
}
运行以后就能看到下边的东西了，json文件里可以看到我们定义的表以及其包含的字段，主键等信息
image.png
版本升级
https://www.jianshu.com/p/df48fb35a1fe
知道升级要添加的方法，可是咋复制老的数据库不记得了，所以还是找别人写的看好了。最讨厌数据库了，2个表就晕了。
打印下可以看到，第一次操作数据库的时候，先create，再open
System.out.println(“onCreate===========”+db.getVersion()+”===”+db.getPath());
onCreate===========0===/data/user/0/com.charliesong.demo0327/databases/test
onOpen===========1===/data/user/0/com.charliesong.demo0327/databases/test
升级操作
如果你改了版本，然后没有写Migration，那么升级以后数据库就被清空了。
这两个方法,要么别写，要写了你就得有对应的migration，
// .addMigrations(migration,migration2)//迁移数据库使用，下面会单独拿出来讲
// .fallbackToDestructiveMigration()//迁移数据库如果发生错误，将会重新创建数据库，而不是发生崩溃
我们一般升级数据库，应该是增加了字段或者修改了字段之类的。
//数据库升级用的,从版本1升级到版本2
static Migration migration=new Migration(1,2) {
@Override
public void migrate(@NonNull SupportSQLiteDatabase database) {
System.out.println("migrate12============"+database.getVersion());
database.execSQL("ALTER TABLE Userjava "+ " ADD COLUMN country TEXT");
}
};
版本2升级到版本4，打算删除表中的一列
如果想改某列的类型，名称啥的也一样操作
.addMigrations(migration,migration2,migration3)
好像drop column不好使，所以就新建个临时表，复制下数据然后删除老的，再把新表名字改回去
static Migration migration2=new Migration(2,3) {
@Override
public void migrate(@NonNull SupportSQLiteDatabase database) {
System.out.println("migrate23============"+database.getVersion());
database.execSQL("create table aaaa(uid int primary key,firstName text,lastName text,age text,address text)");
database.execSQL("insert into aaaa select uid ,firstName ,lastName ,age,address from Userjava");
database.execSQL("drop table Userjava");
database.execSQL("alter table aaaa rename to Userjava");
}
};
static Migration migration3=new Migration(3,4) {
@Override
public void migrate(@NonNull SupportSQLiteDatabase database) {
System.out.println("migrate34============"+database.getVersion());
// database.execSQL("ALTER TABLE Userjava "+ " ADD COLUMN address TEXT");
}
};
日志如下，2个print都出来了，然后挂了
看了下，我们上边新建那个aaaa的表，数据类型有点问题，那就改一下
Process: com.charliesong.demo0327, PID: 30844
java.lang.IllegalStateException: Migration didn't properly handle Userjava(com.charliesong.demo0327.room.Userjava).
Expected:
TableInfo{name='Userjava', columns={address=Column{name='address', type='TEXT', affinity='2', notNull=false, primaryKeyPosition=0}, lastName=Column{name='lastName', type='TEXT', affinity='2', notNull=false, primaryKeyPosition=0}, firstName=Column{name='firstName', type='TEXT', affinity='2', notNull=false, primaryKeyPosition=0}, uid=Column{name='uid', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1}, age=Column{name='age', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0}}, foreignKeys=[], indices=[]}
Found:
TableInfo{name='Userjava', columns={address=Column{name='address', type='text', affinity='2', notNull=false, primaryKeyPosition=0}, lastName=Column{name='lastName', type='text', affinity='2', notNull=false, primaryKeyPosition=0}, firstName=Column{name='firstName', type='text', affinity='2', notNull=false, primaryKeyPosition=0}, uid=Column{name='uid', type='int', affinity='3', notNull=false, primaryKeyPosition=1}, age=Column{name='age', type='text', affinity='2', notNull=false, primaryKeyPosition=0}}, foreignKeys=[], indices=[]}
at com.charliesong.demo0327.room.JavaDatabase_Impl$1.validateMigration(JavaDatabase_Impl.java:75)
at android.arch.persistence.room.RoomOpenHelper.onUpgrade(RoomOpenHelper.java:87)
at android.arch.persistence.db.framework.FrameworkSQLiteOpenHelper$OpenHelper.onUpgrade(FrameworkSQLiteOpenHelper.java:133)
at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:256)
at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:163)
at android.arch.persistence.db.framework.FrameworkSQLiteOpenHelper$OpenHelper.getWritableSupportDatabase(FrameworkSQLiteOpenHelper.java:96)
at android.arch.persistence.db.framework.FrameworkSQLiteOpenHelper.getWritableDatabase(FrameworkSQLiteOpenHelper.java:54)
at android.arch.persistence.room.RoomDatabase.query(RoomDatabase.java:233)
at com.charliesong.demo0327.room.UserJavaDao_Impl$4.compute(UserJavaDao_Impl.java:165)
at com.charliesong.demo0327.room.UserJavaDao_Impl$4.compute(UserJavaDao_Impl.java:151)
at android.arch.lifecycle.ComputableLiveData$2.run(ComputableLiveData.java:100)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)
这是成功的日志
11-15 09:15:27.546 com.charliesong.demo0327 I/System.out: migrate23============2
11-15 09:15:27.556 com.charliesong.demo0327 I/System.out: migrate34============2
11-15 09:15:27.606 com.charliesong.demo0327 I/System.out: onOpen===========4===/data/user/0/com.charliesong.demo0327/databases/test
new Migration(4,6) 里边2个版本号到底指的啥
为了测试，
@1 版本从4直接改到8，然后添加2个Migration
new Migration(4,6)和new Migration(4,8)
打印了下，发现只走了4到8
@2 然后版本从8改成11，添加下边2个
new Migration(8,10) new Migration(9,11)
然后2个都没走，然后数据被清空了
看下Migration的查询条件
存储的时候是存在这个集合里的
private SparseArrayCompat<SparseArrayCompat<Migration>> mMigrations =
new SparseArrayCompat<>();
比如（4,6）和（4,8）那么就是append一个key是4的，然后里边包含的key是6和8的sparsearray
简单分析下，我们只说升级，不说降级。
如下逻辑，从4升级到8，那么根据start=4，找到一个sparsearray，这里包含2个key是6和8，它是倒着来，找到第一个小于等于endVersion也就是8了，这个刚刚好就找一次。
然后分析下从8升级到11，有个（8,10）和（9,11）
先查8，找到一个end10，然后 从10开始查，结果10 没找到，所以返回一个null。因为返回的null。再下边那个方法可以看到，返回null的话数据库就被清空了。
private List<Migration> findUpMigrationPath(List<Migration> result, boolean upgrade,
int start, int end) {
final int searchDirection = upgrade ? -1 : 1;
while (upgrade ? start < end : start > end) {
SparseArrayCompat<Migration> targetNodes = mMigrations.get(start);
if (targetNodes == null) {
return null;
}
// keys are ordered so we can start searching from one end of them.
final int size = targetNodes.size();
final int firstIndex;
final int lastIndex;
if (upgrade) {
firstIndex = size - 1;
lastIndex = -1;
} else {
firstIndex = 0;
lastIndex = size;
}
boolean found = false;
for (int i = firstIndex; i != lastIndex; i += searchDirection) {
final int targetVersion = targetNodes.keyAt(i);
final boolean shouldAddToPath;
if (upgrade) {
shouldAddToPath = targetVersion <= end && targetVersion > start;
} else {
shouldAddToPath = targetVersion >= end && targetVersion < start;
}
if (shouldAddToPath) {
result.add(targetNodes.valueAt(i));
start = targetVersion;
found = true;
break;
}
}
if (!found) {
return null;
}
}
return result;
}
这里是调用的方法
public void onUpgrade(SupportSQLiteDatabase db, int oldVersion, int newVersion) {
boolean migrated = false;
if (mConfiguration != null) {
List<Migration> migrations = mConfiguration.migrationContainer.findMigrationPath(
oldVersion, newVersion);
if (migrations != null) {
for (Migration migration : migrations) {
migration.migrate(db);
}
mDelegate.validateMigration(db);
updateIdentity(db);
migrated = true;
}
}
if (!migrated) {//如果没找到List<Migration> migrations，那么就会清空表的
if (mConfiguration != null && !mConfiguration.isMigrationRequiredFrom(oldVersion)) {
mDelegate.dropAllTables(db);
mDelegate.createAllTables(db);
} else {
throw new IllegalStateException("A migration from " + oldVersion + " to "
+ newVersion + " was required but not found. Please provide the "
+ "necessary Migration path via "
+ "RoomDatabase.Builder.addMigration(Migration ...) or allow for "
+ "destructive migrations via one of the "
+ "RoomDatabase.Builder.fallbackToDestructiveMigration* methods.");
}
}
}
添加一个新的entity
错误日志，说这个实体类没有加到database，啥鬼啊，搞不懂。后来才查到，我去注解那里要添加的，忘了
@Database(entities = {Userjava.class,HourseJava.class},version =1)
public abstract class JavaDatabase extends RoomDatabase
E:\androidStudio\RoomTest\app\src\main\java\com\charliesong\roomtest\room\HourseJavaDao.java:9:
错误: com.charliesong.roomtest.room.HourseJavaDao
is part of com.charliesong.roomtest.room.JavaDatabase
but this entity is not in the database. Maybe you forgot to add com.charliesong.roomtest.room.HourseJava
to the entities section of the @Database?
void insertHourse(HourseJava ...hourseJavas);
^
添加新的entity步骤
需要在database的注解字段entities里添加，完事需要升级版本号，完事记得添加migration，
比如你从2升级到3，那么必须添加一个Migration(2,3)，否则如果没找到这玩意，数据库就被清空了。还得自己在migration方法里添加create table的命令，建立新表，要不会报错的。
后记
room这东西是编译的时候生成相关的类的，databinding也是，有时候是room这边有问题，导致databinding生成失败，结果你看错误信息都是databinding的。
