android - 房间数据库无法预填充数据并且未创建数据库文件
问题描述
我已经Room
在应用程序中实现了数据库。我想在首次打开应用程序时预填充数据。班级Entity
看起来像
@Entity(tableName = NameConstants.TABLE_NAME)
public class Name {
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
@PrimaryKey(autoGenerate = true)
private int id;
@ColumnInfo(name = NameConstants.COL_NAME)
private String Name;
@ColumnInfo(name= NameConstants.COL_PHONE)
private String Phone;
@ColumnInfo(name = NameConstants.COL_CITY)
private String City;
public Name(){
}
public Name(String name, String phone, String city) {
Name = name;
Phone = phone;
City = city;
}
public String getName() {
return Name;
}
public void setName(String name) {
Name = name;
}
public String getPhone() {
return Phone;
}
public void setPhone(String phone) {
Phone = phone;
}
public String getCity() {
return City;
}
public void setCity(String city) {
City = city;
}
}
DAO
实现是
@Dao
public interface NameDAO {
@Insert(onConflict = OnConflictStrategy.REPLACE)
void insertAll(Name... names);
@Insert(onConflict = OnConflictStrategy.REPLACE)
void insert(Name name);
@Delete
void delete(Name name);
}
该类Database
似乎是这样的,从一个Raw
文件中读取数据
@Database(entities = {Name.class},version = 1,exportSchema = false)
public abstract class NameDatabase extends RoomDatabase {
public abstract NameDAO nameDAO();
private static volatile NameDatabase dInstance=null;
static synchronized NameDatabase getInstance(final Context context){
if(dInstance==null){
synchronized (NameDatabase.class){
if(dInstance==null){
dInstance= Room.databaseBuilder(context.getApplicationContext(),NameDatabase.class,"appdatabase")
.allowMainThreadQueries()
.addCallback(new Callback() {
@Override
public void onCreate(@NonNull SupportSQLiteDatabase db) {
super.onCreate(db);
fillWithDemoData(context);
}
}
).build();
}
}
}
return dInstance;
}
@WorkerThread
private static void fillWithDemoData(Context context){
NameDAO dao=getInstance(context).nameDAO();
JSONArray emoji = loadJsonArray(context);
try {
for (int i = 0; i < emoji.length(); i++) {
JSONObject item = emoji.getJSONObject(i);
dao.insert(new Name(item.getString("name"),
item.getString("phone"),
item.getString("city")));
}
} catch (JSONException exception) {
exception.printStackTrace();
}
}
private static JSONArray loadJsonArray(Context context) {
StringBuilder builder = new StringBuilder();
InputStream in = context.getResources().openRawResource(R.raw.namesdata);
BufferedReader reader = new BufferedReader(new InputStreamReader(in));
String line;
try {
while ((line = reader.readLine()) != null) {
builder.append(line);
}
JSONObject json = new JSONObject(builder.toString());
return json.getJSONArray("names");
} catch (IOException | JSONException exception) {
exception.printStackTrace();
}
return null;
}
}
Repository
班级是公开的
class DataRepository {
private NameDAO nDao;
public DataRepository(Application application) {
NameDatabase database = NameDatabase.getInstance(application);
nDao = database.nameDAO();
}
}
当应用程序安装并打开应用程序工作正常时,没有崩溃,但没有创建数据库文件,也没有数据插入数据库。代码中还缺少什么或有什么问题?
解决方案
当应用程序安装并打开应用程序工作正常时,没有崩溃,但没有创建数据库文件,也没有数据插入数据库。
如果您没有崩溃,那么我相信您没有对数据库做任何其他事情。只需构建它并获取实例。
在您尝试访问数据库之前,不会创建数据库。您需要尝试对数据库做一些事情。
然而!!!!!
然后你会得到一个java.lang.IllegalStateException: getDatabase called recursively
FATAL 异常。
基本上,通过访问数据库,您然后尝试打开它,因为数据库不存在,所以调用 onCreate 回调,然后通过插入访问它的 attemtp 将尝试打开数据库,从而进行递归。
简而言之,您只能通过传递给 onCreate 的 SupportSQLiteDatabase 访问数据库。
你可以使用:-
public static void fillWithDemoData(Context context, SupportSQLiteDatabase sdb){
ContentValues cv = new ContentValues(); //<<<<<<<<<< ADDED
JSONArray emoji = loadJsonArray(context);
try {
for (int i = 0; i < emoji.length(); i++) {
JSONObject item = emoji.getJSONObject(i);
//<<<<<<<<<< CANNOT USE ROOM here >>>>>>>>>
//dao.insert(new Name(item.getString("name"),
// item.getString("phone"),
// item.getString("city")));
cv.clear();
cv.put(NameConstants.COL_NAME,item.getString(NameConstants.COL_NAME));
cv.put(NameConstants.COL_CITY,item.getString(NameConstants.COL_CITY));
cv.put(NameConstants.COL_PHONE,item.getString(NameConstants.COL_PHONE));
sdb.insert(NameConstants.TABLE_NAME, OnConflictStrategy.IGNORE,cv);
}
} catch (JSONException exception) {
exception.printStackTrace();
}
}
但是您需要尝试访问 ROOM,例如,在您的活动或等效项中,您可以使用:-
ndb = NameDatabase.getInstance(this); //<<<<<<<<<< ROOM databse not yet created (opened)
ndb.getOpenHelper(); //<<<<<<<<<< FORCE OPEN and thus create (or just access the db via a Dao call)
示例/演示/测试
由于我无权访问您的 JSON 文件,因此我使用以下方法测试了上述内容:-
@WorkerThread
public static void fillWithDemoData(Context context, SupportSQLiteDatabase sdb){
ContentValues cv = new ContentValues(); //<<<<<<<<<< ADDED
cv.clear();
cv.put(NameConstants.COL_NAME,"Fred");
cv.put(NameConstants.COL_CITY,"London");
cv.put(NameConstants.COL_PHONE,"0000000000");
sdb.insert(NameConstants.TABLE_NAME, OnConflictStrategy.IGNORE,cv);
/*
JSONArray emoji = loadJsonArray(context);
try {
for (int i = 0; i < emoji.length(); i++) {
JSONObject item = emoji.getJSONObject(i);
//<<<<<<<<<< CANNOT USE ROOM here >>>>>>>>>
//dao.insert(new Name(item.getString("name"),
// item.getString("phone"),
// item.getString("city")));
cv.clear();
cv.put(NameConstants.COL_NAME,item.getString(NameConstants.COL_NAME));
cv.put(NameConstants.COL_CITY,item.getString(NameConstants.COL_CITY));
cv.put(NameConstants.COL_PHONE,item.getString(NameConstants.COL_PHONE));
sdb.insert(NameConstants.TABLE_NAME, OnConflictStrategy.IGNORE,cv);
}
} catch (JSONException exception) {
exception.printStackTrace();
}
*/
}
- 还注释掉了loadJsonArray中的代码
使用的活动是:-
public class MainActivity extends AppCompatActivity {
NameDatabase ndb;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ndb = NameDatabase.getInstance(this);
ndb.getOpenHelper(); //<<<<<<<<<< FORCE OPEN and thus create (not needed as db accessed below)
//This would also do the same, this used to test the data//
List<Name> nameList = ndb.nameDAO().getALl();
for (Name n: nameList) {
logName(n);
}
}
private void logName(Name n) {
Log.d("NAMEINFO","Name is " + n.getName() + "\n\tCity is " + n.getCity() + "\n\tPhone is " + n.getPhone() + "ID is " + n.getId());
}
}
结果
安装后首次运行:-
2019-11-14 08:22:08.483 D/ONCREATE: onCreate has been called 2019-11-14 08:22:08.492 D/NAMEINFO: Name is Fred City is London Phone is 0000000000ID is 1
- 未将日志添加到 onCreate 中,因此它表明它已被调用。
第二次运行:-
2019-11-14 08:23:22.532 D/NAMEINFO: Name is Fred City is London Phone is 0000000000ID is 1
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