i am trying to update a value and fetch it from a sqlite database :
private static final String TABLE_INTERVALLE_DE_MESURE = "intervalle_de_mesure";
private static final String COLONNE_ID = "_id";
private static final String COLONNE_VALEUR = "valeur";
private static final String CREATE_INTERVALLE_DE_MESURE =
"create table " TABLE_INTERVALLE_DE_MESURE " ("
COLONNE_ID " integer primary key autoincrement, "
COLONNE_VALEUR " integer default 0);";
public MaBD_IntervalleDeMesure (Context context) {
super(context, dbName, null, dbVersion) ;
}
public void updateIntervalle(int intervalle) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(COLONNE_VALEUR, intervalle);
db.update(TABLE_INTERVALLE_DE_MESURE, values, COLONNE_ID " = ?", new String[] {Long.toString(1)});
db.close();
}
public int getIntervalle() {
int res = 0;
SQLiteDatabase db = this.getReadableDatabase();
String maRequeteIntervalle = "SELECT " COLONNE_VALEUR " FROM " TABLE_INTERVALLE_DE_MESURE ";";
Cursor cursor = db.rawQuery(maRequeteIntervalle, null);
if (cursor.getCount() != 0) {
cursor.moveToFirst();
res = cursor.getInt(0);
}
cursor.close();
db.close();
return res;
}
}
the return of db.update in the updateIntervalle function returns me a number other than -1.
However, cursor.getCount() returns me 0. Why ?
CodePudding user response：
the return of db.update in the updateIntervalle function returns me a number other than -1.
There appears to be nothing wrong with the code. However, the update convenience method will never return -1. It returns the number of rows that have been updated or 0 if none.
However, cursor.getCount() returns me 0. Why ?
At a guess, because there is no data in the table.
- Perhaps you are assuming that the update method will add a row. It will not, it will only update existing rows. If so then you will need to insert a row.
Demonstration
Using the following adaptation of your code :-
class MaBD_IntervalleDeMesure extends SQLiteOpenHelper {
public static final String TABLE_INTERVALLE_DE_MESURE = "intervalle_de_mesure";
public static final String COLONNE_ID = "_id";
public static final String COLONNE_VALEUR = "valeur";
private static final String DBNAME = "mydb";
private static final int DBVERSION = 1;
private static final String CREATE_INTERVALLE_DE_MESURE =
"create table " TABLE_INTERVALLE_DE_MESURE " ("
COLONNE_ID " integer primary key autoincrement, "
COLONNE_VALEUR " integer default 0);";
public MaBD_IntervalleDeMesure (Context context) {
super(context, DBNAME, null, DBVERSION) ;
}
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
sqLiteDatabase.execSQL(CREATE_INTERVALLE_DE_MESURE);
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
}
public void updateIntervalle(int intervalle) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(COLONNE_VALEUR, intervalle);
int rv = db.update(TABLE_INTERVALLE_DE_MESURE, values, COLONNE_ID " = ?", new String[] {Long.toString(1)});
Log.d("DBINFO","Result of updateIntervalle is " rv " (0 = nothing update > 0 = number of rows updated");
//db.close(); closing database is inefficient
}
public int getIntervalle() {
int res = 0;
SQLiteDatabase db = this.getReadableDatabase();
String maRequeteIntervalle = "SELECT " COLONNE_VALEUR " FROM " TABLE_INTERVALLE_DE_MESURE ";";
Cursor cursor = db.rawQuery(maRequeteIntervalle, null);
if (cursor.getCount() != 0) {
cursor.moveToFirst();
res = cursor.getInt(0);
}
cursor.close();
//db.close(); again closing is inefficient
return res;
}
}
along with an activity MainActivity as :-
public class MainActivity extends AppCompatActivity {
MaBD_IntervalleDeMesure dbhelper;
SQLiteDatabase db;
public static final String TAG = "DBINFO";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// TEST 1 - Get from empty table
dbhelper = new MaBD_IntervalleDeMesure(this);
Log.d(TAG,"Test 1 - empty database results in " dbhelper.getIntervalle());
// TEST 2 - Update noithing as empty table
Log.d(TAG,"Test 2 - update of empty database (check log for result logged by update)");
dbhelper.updateIntervalle(1);
// TEST 3 - Insert new row (id will very likely be 1)
ContentValues cv = new ContentValues();
cv.put(MaBD_IntervalleDeMesure.COLONNE_VALEUR,999);
db = dbhelper.getWritableDatabase();
db.insert(MaBD_IntervalleDeMesure.TABLE_INTERVALLE_DE_MESURE,null,cv);
Log.d(TAG,"Test 3 - update of empty database (check log for result logged by update)");
dbhelper.updateIntervalle(888);
Log.d(TAG,"Test 4 - database with a single row results in " dbhelper.getIntervalle());
}
}
Then the log includes:-
2022-01-06 08:12:03.314 D/DBINFO: Test 1 - empty database results in 0
2022-01-06 08:12:03.314 D/DBINFO: Test 2 - update of empty database (check log for result logged by update)
2022-01-06 08:12:03.315 D/DBINFO: Result of updateIntervalle is 0 (0 = nothing update > 0 = number of rows updated
2022-01-06 08:12:03.315 D/DBINFO: Test 3 - update of empty database (check log for result logged by update)
2022-01-06 08:12:03.316 D/DBINFO: Result of updateIntervalle is 1 (0 = nothing update > 0 = number of rows updated
2022-01-06 08:12:03.317 D/DBINFO: Test 4 - database with a single row results in 888
So:-
Test 1 runs your getIntervalle method which returns 0 as there is no data in the table at this stage.
Test 2 reports that the updateIntervalle method does nothing, as there are no rows in the table to update.
TEST 3 reports, as now there is a suitable row (who's id is 1), that 1 row was updated.
TEST 4 reports that the value 888 (updated from 999) has been extracted.
Additionally is App Inspection is used then the database can be viewed it shows:-
