Develop Reference

Returning sqlite query as cursor or object/list

When I started my app years ago, I did some tutorials and always did my queries to the database returning the cursor (without closing it):
public Cursor querySingleId(String szId) {
SQLiteDatabase db = getWritableDatabase();
return db.query(TABLE_ADR, szGetTableEntries, _ID + " = ?", new String[]{szId}, null, null, null);
}
Now I am refactoring my code to MVVM and added models, so I changed my code to this:
public Card querySingleId(String szId) {
SQLiteDatabase db = getWritableDatabase();
Cursor c1 = db.query(TABLE_ADR, szGetTableEntries, _ID + " = ?", new String[]{szId}, null, null, null);
c1.moveToFirst();
return new Card(c1.getString(c1.getColumnIndex(DbHandler.NAME)),
c1.getString(c1.getColumnIndex(DbHandler.STREET)),
c1.getString(c1.getColumnIndex(DbHandler.CITY)));
}
I read that cursors should always be closed (memory leak). Which is the best/most conform approach to return my data from the database? I'm also unsure if there are multiple results, should I stay with a cursor or change to a list?
public List<Card> queryAll() {
SQLiteDatabase db = getWritableDatabase();
Cursor c1 = db.query(TABLE_ADR, szGetTableEntries, null, null, null, null, null);
List<Card> list = new ArrayList<>();
if(c1.moveToFirst()){
do{
list.add(new Card(c1.getString(c1.getColumnIndex(DbHandler.NAME)),
c1.getString(c1.getColumnIndex(DbHandler.STREET)),
c1.getString(c1.getColumnIndex(DbHandler.CITY))));
} while(c1.moveToNext());
}
c1.close();
return list;
}
Is this all just a matter of taste or are there reasons why it should return a cursor or a list/object? Depending where in my code I need the data, a list or a cursor is more convenient.
I'm just not sure what is the correct approach in sqlite queries. There are so many code examples and but it seems most is copy/paste without really digging into the topic.

If the query can return multiple rows then you should return a list.
If you are sure that the query will return just a single Card then returning that single Card would be OK (probably preferable) BUT you should close the Cursor.
However, there isn't an actual requirement/need to do so (e.g. if you your initial activity uses a Cursor for a ListView/Spinner then you may not want to close the Cursor but reuse it and use the adapter's swapCursor when the Activity resumes). The cursor would be effectively closed, as would the database when the App finishes.
As you have used the column _ID which is typically used for a column that is an alias of the rowid column, which is typically generated by SQLite then if used/defined as such (column has been defined explicitly or implicitly as INTEGER PRIMARY KEY with or without AUTOINCREMENT) then it will be a unique value and only return a single row as you have _ID = ?. As such there is a high likeliehood that a single row, or no row would be returned, and unlikely that multiple rows are returned.
So (for a single Card):-
public Card querySingleId(String szId) {
SQLiteDatabase db = getWritableDatabase();
Cursor c1 = db.query(TABLE_ADR, szGetTableEntries, _ID + " = ?", new String[]{szId}, null, null, null);
c1.moveToFirst();
return new Card(c1.getString(c1.getColumnIndex(DbHandler.NAME)),
c1.getString(c1.getColumnIndex(DbHandler.STREET)),
c1.getString(c1.getColumnIndex(DbHandler.CITY)));
}
Should be something like :-
public Card querySingleId(String szId) {
SQLiteDatabase db = getWritableDatabase();
Card rv = null;
Cursor c1 = db.query(TABLE_ADR, szGetTableEntries, _ID + " = ?", new String[]{szId}, null, null, null);
if (c1.moveToFirst()) { //<<<<<< Should always check if the move moved
rv = new Card(c1.getString(c1.getColumnIndex(DbHandler.NAME)),
c1.getString(c1.getColumnIndex(DbHandler.STREET)),
c1.getString(c1.getColumnIndex(DbHandler.CITY)));
}
c1.close();
return rv; //<<<<< Note should check the returned Card for null
}
In addition to memory leaks not closing Cursors can result in a too many open connections (1K (1024) if memory serves correctly) and then a exception: unable to open database file (code 14); as underneath all the wrappers a Cursor has a file associated with it.

How to write a sqlite query to get specific data?

I want to get the first name, middle name and last name of a student whose userid is used for login. I have written this particular piece of code but it stops my application.
I have used both the ways like database.query() and .rawquery() also.
Cursor studentData(String userId) {
SQLiteDatabase db = getWritableDatabase();
Cursor cursor = db.query(studentTable, new String[] { "First_Name", "Middle_Name", "Last_Name"}, "User_ID=?", new String[] { userId }, null, null, null, null);
// Cursor cursor = db.rawQuery("select First_Name, Middle_Name, Last_Name from Student_Table where User_ID =?", new String[]{userId});
String data = cursor.getString(cursor.getColumnIndex("First_Name"));
db.close();
return cursor;
}
I should get whole name in the string.

You have a number of issues.
Attempting to use String data = cursor.getString(cursor.getColumnIndex("First_Name"));,
will result in an error because you have not moved the cursor beyond BEFORE THE FIRST ROW and the attempt to access the row -1 will result in an exception (the likely issue you have encountered).
you can use various move??? methods e.g. moveToFirst, moveToNext (the 2 most common), moveToLast, moveToPosition.
Most of the Cursor move??? methods return true if the move could be made, else false.
You CANNOT close the database and then access the Cursor (this would happen if the issue above was resolved)
The Cursor buffers rows and then ONLY when required.
That is The Cursor is when returned from the query method (or rawQuery) at a position of BEFORE THE FIRST ROW (-1), it's only when an attempt is made to move through the Cursor that the CursorWindow (the buffer) is filled (getCount() included) and the actual data obtained. So the database MUST be open.
If you want a single String, the full name, then you could use :-
String studentData(String userId) { //<<<<<<<<<< returns the string rather than the Cursor
SQLiteDatabase db = getWritableDatabase();
String rv = "NO NAME FOUND"; //<<<<<<<<<< value returned if no row is located
Cursor cursor = db.query(studentTable, new String[] { "First_Name", "Middle_Name", "Last_Name"}, "User_ID=?", new String[] { userId }, null, null, null, null);
if (cursor.modeToFirst()) {
String rv =
cursor.getString(cursor.getColumnIndex("First_Name")) +
" " +
cursor.getString(cursor.getColumnIndex("Middle_Name")) +
" " +
cursor.getString(cursor.getColumnIndex("Last_Name"));
}
cursor.close(); //<<<<<<<<<< should close all cursors when done with them
db.close(); //<<<<<<<<<< not required but would result in an exception if returning a Cursor
return rv;
}
Or alternately :-
String studentData(String userId) { //<<<<<<<<<< returns the string rather than the Cursor
SQLiteDatabase db = getWritableDatabase();
String rv = "NO NAME FOUND"; //<<<<<<<<<< value returned if no row is located
Cursor cursor = db.query(studentTable, new String[] { "First_Name"||" "||"Middle_Name"||" "||"Last_Name" AS fullname}, "User_ID=?", new String[] { userId }, null, null, null, null);
if (cursor.modeToFirst()) {
String rv =
cursor.getString(cursor.getColumnIndex("fullname"));
}
cursor.close(); //<<<<<<<<<< should close all cursors when done with them
db.close(); //<<<<<<<<<< not required but would result in an exception if returning a Cursor
return rv;
}
the underlying query being SELECT First_Name||" "||Middle_Name||" "||LastName AS fullname FROM student_table; so you concatenate the names as part of the query which returns just one dynamically created column named fullname.

Android Close dataBase Failed

with simple below code i get this error for close database or cursor:
Database﹕ close() was never explicitly called on database '/data/data/ir.tsms/databases/tsms'
android.database.sqlite.DatabaseObjectNotClosedException:
My Function:
public Boolean searchLastID( Long lastID){
SQLiteDatabase db = this.getReadableDatabase();
String selectQuery = "SELECT * FROM " + this.RECEIVE_FIELDS_TABLE + " WHERE lastId = ?" ;
String[] args = {String.valueOf(lastID)};
Cursor cursor = db.rawQuery(selectQuery, args);
//db.close();
return cursor.moveToFirst();
}
after uncommenting db.close();
Cursor﹕ Finalizing a Cursor that has not been deactivated or closed. database = /data/data/ir.tsms/databases/tsms, table = null, query = SELECT * FROM ReceiveFields WHERE lastId = ?
whats problem and how to resolve that? i can't find any document about this problem. Thanks

make your cursor a global variable
and inside your onDestory Method close your cursor and your database
#Override
protected void onDestroy() {
super.onDestroy();
cursor.close();
db.close();
}

As soon as you're done retrieving the data of your query from your database you should close the Cursor or at least deactivate it. (Keyword: Freeing resources)
Following two quotes from the Docs on the close() and deactivate() method:
#close()
Closes the Cursor, releasing all of its resources and making it
completely invalid. Unlike deactivate() a call to requery() will not
make the Cursor valid again.
#deactivate()
Deactivates the Cursor, making all calls on it fail until requery() is
called. Inactive Cursors use fewer resources than active Cursors.
Calling requery() will make the cursor active again.

Sqlite open helper insert else update?

I want to insert data successfully
Here is my code:
public void insertData(String strTableName,
ArrayList<HashMap<String, String>> arrListproductdatabase) {
db = this.getWritableDatabase();
ContentValues cv = new ContentValues();
for (int i = 0; i < arrListproductdatabase.size(); i++) {
// cv.put(columnName, arrListOfRecord.get(i).get("name"));
cv.put(columnproductname,
arrListproductdatabase.get(i).get("product"));
cv.put(columnproductprice,
arrListproductdatabase.get(i).get("price"));
cv.put(columnproductquantity,
arrListproductdatabase.get(i).get("quantity"));
cv.put(columnproductid,
arrListproductdatabase.get(i).get("productID"));
cv.put(columnresturantID,
arrListproductdatabase.get(i).get("resturantID"));
db.insert(strTableName, null, cv);
}
I want that when I have to press add button again, that time it should check if the product is already inserted, and in that condition it should update and all.
I don't want to create any duplicate value.
Any help would be appreciated!

you can check for the distinct values in the db. please follow the link to have more details
android check duplicate values before inserting data into database

Set 'Product' field as unique key. So when duplicate value arrives from standard insert, it will simply return -1 and the error message will be swallowed.
You can control the behavior by using insertWithOnConflict (String table, String nullColumnHack, ContentValues initialValues, int conflictAlgorithm) where you also specify a conflict algorithm that can be of values:
CONFLICT_ABORT
CONFLICT_FAIL
CONFLICT_IGNORE
CONFLICT_REPLACE
CONFLICT_ROLLBACK
Check out the reference for descrption of the conflict resolution types.
There is also an updateWithOnConflict

You can do that like this :
public boolean checkProduct(String product){
// shold open database here
Cursor mCursor =
db.query(true, DATABASE_TABLE, null, "product='" + product+"'", null, null, null, null, null);
if(mCursor != null){
mCursor.close();
// shold close database here
return true;
}
// shold close database first here also
return false;
}
Hope this helped you.

Retrieve data from SQLite database

inHow do i retrieve data from sqlite database from adapter class and insert to listview???
I'm having difficulty, been coding day & night and googling non-stop but i just don't understand the links when i open them up. I just start learning android programming recently on my own...
I have attach my code below
public Cursor RetrieveActivityCursor(String NRIC){
String where = NRIC;
Cursor cursor = _db.query(DATABASE_TABLE,new String[]{ MOBILE_HOUSE_VISIT_ID, ELDERLY_NAME,
ELDERLY_NRIC, ELDERLY_DATE_TIME, PHYSICAL_HEALTH_STATUS, MENTAL_HEALTH_STATUS} , where, null, null, null, null);
//Cursor cursor = _db.query(DATABASE_TABLE, new String[] { ELDERLY_NAME,
//ELDERLY_NRIC, DATE_TIME, PHYSICAL_HEALTH_STATUS, MENTAL_HEALTH_STATUS }, null, null, null, null, null);
return cursor;
}
this code is from my adapter class and have to pass in nric and return datetime value inserted into listview
im not too sure how to code to call this method.

If you are extending the SqliteOpenHelper for the database handling and using another class to which extends Activity, in which you have your ListView then, in your Activity class make the object of your class like,
YourDBClass helperDB;
helperDB = new HelperDB(YourActivityClass.this);
And to retrive the data from the Database.
Make Cursor reference like,
Cursor cursor;
And then, do like this,
cursor = helperDB.RetrieveActivityCursor(NRIC);
cursor.moveToFirst();
while(!cursor.isAfterLast()) {
// here you have to collect the data in the collection object.
cursor.moveToNext();
}
cursor.close();
That's it! And you have done with retriving data from database

you need iterate cursor, like this:
Cursor cursor = RetrieveActivityCursor(NRIC);
if (cursor != null && cursor.moveToNext())
do {
String str = cursor.getString(cursor.getColumnIndex("your_column"));
// do something, your code
} while (cursor.moveToNext());

Where you like to retrieve the date value do the below over there.
Cursor cursor = RetrieveActivityCursor(NRIC);
if(mCursor.moveToFirst()) {
do{
String date_time = cursor.getString(cursor.getColumnIndex(column_name));
} while(mCursor.moveToNext());
}
cursor.close();