我正在使用 sqlite LocationsContentProvider 开发一个 Android 应用程序。我在加入时遇到了一些麻烦。
这工作正常:
// Returns all the locations from the table
public Cursor getAllLocations(){
Cursor cursor;
cursor = mDB.query(DATABASE_TABLE, new String[] { FIELD_ROW_ID, FIELD_LAT , FIELD_LNG, FIELD_ZOOM, FIELD_ADDRESS } , null, null, null, null, null);
Log.d(TAG, "DB: query complete" + cursor );
return cursor;
}
这不起作用:
// Return all locations joined with sub map name
public Cursor getAllLocations(){
Cursor cursor;
String query;
query = "SELECT a._id, a.lat, a.lng, a.sub_map_id, a.zoom, a.address, b._id, b.sub_map FROM locations a" +
" INNER JOIN sub_map_table b ON a.sub_map_id=b._id";
Log.d(TAG, "DB: query = \n" + query;
Log.d(TAG, "DB: query complete" );
cursor = mDB.rawQuery(query, null);
return cursor;
}
关于数据库结构的其他一些细节:
// Fields for locations table
public static final String FIELD_ROW_ID ="_id";
public static final String FIELD_LAT = "lat";
public static final String FIELD_LNG = "lng";
public static final String FIELD_ZOOM = "zoom";
public static final String FIELD_ADDRESS ="address";
public static final String FIELD_SUB_MAP_ID = "sub_map_id";
// Fields for SUB_MAP_TABLE table
public static final String FIELD_SUB_MAP_ROW_ID = "_id";
public static final String FIELD_SUB_MAP = "sub_map";
//table name, a constant
private static final String DATABASE_TABLE = "locations";
private static final String SUB_MAP_TABLE = "sub_map_table";
private static final String TAG = null;
//instance variable for SQLiteDatabse
private SQLiteDatabase mDB;
//constructor
public LocationsDB(Context context) {
super(context, DBNAME, null, VERSION);
this.mDB = getWritableDatabase();
}
/** This is a callback method, invoked when the method getReadableDatabase() / getWritableDatabase() is called
* provided the database does not exists
* */
@Override
public void onCreate(SQLiteDatabase db) {
String create_table_locations = "create table " + DATABASE_TABLE + " ( " +
FIELD_ROW_ID + " integer primary key autoincrement , " +
FIELD_LNG + " double , " +
FIELD_LAT + " double , " +
FIELD_ZOOM + " text , " +
FIELD_ADDRESS + " text , " +
FIELD_SUB_MAP_ID + " integer " +
" ) ";
String create_table_submap = "create table " + SUB_MAP_TABLE + " ( " +
FIELD_SUB_MAP_ROW_ID + " integer primary key autoincrement , " +
FIELD_SUB_MAP + " text " +
" ) ";
db.execSQL(create_table_locations);
db.execSQL(create_table_submap);
一整天都在看这个,我不知道出了什么问题。请给我提意见。好像什么都没有发送?或者如果它是通过发送的,它不会被捕获。