如何解决为什么 Room 不从资产填充数据库?
我正在尝试使用 Room 的 assets
方法从 createFromAssets
文件夹复制预先填充的 SQLite 数据库。数据库很大(一张表有大约 37 万个条目;总大小约为 18 mb)。数据库是在 databases
文件夹中创建的,它包含适用的表,但没有数据传输到表中。
我已经查看了以下 SO 问题,但没有找到解决方案:
- How to pre-populate Room Database from asset?
- Room: Database not created
- How To recreate Room Database From Assets?
- Android Room Library fails to copy database from Asset
- Room: Database not created
我还查看了以下信息页面:
- Prepopulate your Room database
- RoomDatabase.Builder
- Packing the Room: pre-populate your database with this one method
- Android Room with a View - Java - Codelab
我试过等待几分钟,看看填充数据库是否需要时间,但没有出现任何数据。我一直在使用 AS 的设备文件资源管理器从虚拟设备下载数据库,并在 SQLite 的 DB 浏览器中打开它,以及使用 AS 的数据库检查器。
此外,LogCat 始终显示以下内容(每次登录 MainActivity):
D/MainActivity: onCreate 1st 10 good words NOT FOUND
GoodWordsAndFrequency.db 结构:
表 1 - “bad_words”
第 1 列 - “单词”,文本
表 2 - “english_words”
第 1 列 - “id”,整数
第 2 列 - “单词”,文本
第 3 列 - “频率”,整数
app build.gradle 依赖:
dependencies {
implementation fileTree(dir: 'libs',include: ['*.jar'])
testImplementation 'junit:junit:4.13.1'
implementation 'androidx.appcompat:appcompat:1.3.1'
implementation 'com.google.android.material:material:1.4.0'
// For Room database
def room_version = "2.3.0"
implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version"
testImplementation "androidx.room:room-testing:$room_version"
}
ValidWords 实体:
import androidx.annotation.NonNull;
import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;
@Entity(tableName = "english_words")
public class ValidWords {
@PrimaryKey(autoGenerate = true)
@ColumnInfo(name = "id")
public int mID;
@ColumnInfo(name = "word")
@NonNull
public String mWord;
@ColumnInfo(name = "frequency")
public int mFrequency;
public ValidWords(@NonNull String word) {this.mWord = word;}
public String getWord() {return this.mWord;}
public void setWord(@NonNull String word) {this.mWord = word;}
public int getFrequency() {return mFrequency;}
public void setFrequency(int frequency) {this.mFrequency = frequency;}
}
BadWords 实体:
import androidx.annotation.NonNull;
import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;
@Entity (tableName = "bad_words")
public class BadWords {
@PrimaryKey
@NonNull
@ColumnInfo(name = "word")
public String mWord;
public BadWords(@NonNull String word) {this.mWord = word;}
@NonNull
public String getWord() {return mWord;}
public void setWord(@NonNull String mWord) {this.mWord = mWord;}
}
wordDAO 接口:
import androidx.room.Dao;
import androidx.room.Insert;
import androidx.room.Query;
import java.util.List;
@Dao
public interface wordsDAO {
@Query("SELECT * FROM english_words LIMIT 10")
List<ValidWords> getFirstTenGoodWords();
@Query("SELECT * FROM bad_words")
List<BadWords> getBadWords();
@Query("SELECT * FROM english_words WHERE word LIKE :wordToCheck LIMIT 1")
ValidWords getMatch(String wordToCheck);
@Insert(entity = ValidWords.class)
long insertGoodWordInfo(ValidWords validWord);
}
ReferenceWordsDB 数据库:
import android.content.Context;
import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;
@Database(entities = {BadWords.class,ValidWords.class},version = 2)
public abstract class ReferenceWordsDB extends RoomDatabase {
public abstract wordsDAO wordsDAO();
private static volatile ReferenceWordsDB INSTANCE;
static ReferenceWordsDB getDatabase(final Context context){
if (INSTANCE == null){
synchronized (ReferenceWordsDB.class){
if (INSTANCE == null){
INSTANCE = Room.databaseBuilder(context.getApplicationContext(),ReferenceWordsDB.class,"GoodWordsAndFrequency.db")
.createFromAsset("GoodWordsAndFrequency.db")
.fallbackToDestructiveMigration()
.allowMainThreadQueries()
.build();
}
}
}
return INSTANCE;
}
}
主要活动:
import android.content.Context;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.inputmethod.EditorInfo;
import android.view.inputmethod.InputMethodManager;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.core.content.res.ResourcesCompat;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
public class MainActivity extends AppCompatActivity {
private static ArrayList<ArrayList<ValidWords>> infoFromFindActualWordRunnableClass;
private final String LOG_CLASS = "MainActivity";
private ReferenceWordsDB wordsDB;
@Override
protected void onCreate(Bundle savedInstanceState) {
final String METHOD = "onCreate";
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getViews();
wordsDB = ReferenceWordsDB.getDatabase(this);
List<ValidWords> first10GoodWords = new ArrayList<>(wordsDB.wordsDAO().getFirstTenGoodWords());
if (first10GoodWords.size() == 0){
Log.d(LOG_CLASS,String.format(Locale.US,"%s 1st 10 good words NOT FOUND",METHOD));
}
for (ValidWords currentWord : first10GoodWords){
Log.d(LOG_CLASS,"%s currentWord word = %s,frequency = %d",METHOD,currentWord.getWord(),currentWord.getFrequency()));
}
...
}
}
我使用的是 Android Studio 4.2.2,并安装了所有已知更新。
解决方法
据猜测,可能的问题是数据库因迁移不存在而与 .fallbackToDestructiveMigration()
的使用不结合而被破坏,因此数据库为空但在其他方面有效。
因此,您应该检查源数据库的版本(Db Browesr 的 Edit Pragmas 中的 user_version)。它必须与@Database 中代码中的版本相匹配。在您的情况下,您有 @Database(entities = {BadWords.class,ValidWords.class},version = 2)
,因此 user_version id DB Browser 应该是 2。
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