How can I get the number of rows updated using an update statement in SQLite in Android?
Note that I need to use some type of raw execute of a SQL statement, rather than do anything with ContentValues because I need a dynamic query. Thus I can't make use of the SQLiteDatabase.update() method. For example, I'm running something like
UPDATE my_table
SET field_name = field_name + 1
The methods I know of return void, e.g. SQLiteDatabase.execSQL(). SQLiteDatabase.rawQuery() returns a Cursor, but the cursor has zero rows and its count is always -1.
You could do your insert whichever way you want, and then do a select and use the changes() function to return the number of affected rows.
To expand on Mat's answer, here's the example code for getting the updated row count:
Cursor cursor = null;
try
{
cursor = db.rawQuery("SELECT changes() AS affected_row_count", null);
if(cursor != null && cursor.getCount() > 0 && cursor.moveToFirst())
{
final long affectedRowCount = cursor.getLong(cursor.getColumnIndex("affected_row_count"));
Log.d("LOG", "affectedRowCount = " + affectedRowCount);
}
else
{
// Some error occurred?
}
}
catch(SQLException e)
{
// Handle exception here.
}
finally
{
if(cursor != null)
{
cursor.close();
}
}
Expanding on Mat and Pang's answers...
Could we skip the Cursor and use simpleQueryForLong()?
e.g.
public long getChangesCount() {
SQLiteDatabase db = getReadableDatabase();
SQLiteStatement statement = db.compileStatement("SELECT changes()");
return statement.simpleQueryForLong();
}
You can use SQLiteStatement.executeUpdateDelete method for this:
SQLiteDatabase db = getReadableDatabase();
SQLiteStatement statement = db.compileStatement("[your sql here]");
int affectedRows = statement.executeUpdateDelete();
The same method used internally in SQLiteDatabase.update(...) methods.
Related
I am using custom adapter extending cursor adapter for displaying data in listview, to display particular phone number i have passed the id to a method in database class but it is showing
errorandroid.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
while placing debugger in the the method it is not going after the line
num = cursor.getString(cursor.getColumnIndex("ContactNumber"));
Can any one help me to solve it.
This is the code:
public String getNumberFromId(int id)
{
String num;
db= this.getReadableDatabase();
Cursor cursor = db.query(scheduletable, new String[] { "ContactNumber" },"_id="+id, null, null, null, null);
cursor.moveToFirst();
num = cursor.getString(cursor.getColumnIndex("ContactNumber"));
cursor.close();
db.close();
return num;
}
Whenever you are dealing with Cursors, ALWAYS check for null and check for moveToFirst() without fail.
if( cursor != null && cursor.moveToFirst() ){
num = cursor.getString(cursor.getColumnIndex("ContactNumber"));
cursor.close();
}
Place logs appropriately to see whether it is returning null or an empty cursor. According to that check your query.
Update Put both the checks in a single statement as mentioned by Jon in the comment below.
Update 2 Put the close() call within the valid cursor scope.
try this.. this will avoid an Exception being thrown when the cursor is empty..
if(cursor != null && cursor.moveToFirst()){
num = cursor.getString(cursor.getColumnIndex("ContactNumber"));
cursor.close();
}
First check this Condition before fetching data
if(cursor!=null && cursor.getCount()>0){
cursor.moveToFirst();
num = cursor.getString(cursor.getColumnIndex("ContactNumber"));
}
Check the return value from moveToFirst(), before you try to read anything from the cursor. It looks as if no results are being returned.
a save schema to query Cursors is
// just one
Cursor cursor = db.query(...);
if (cursor != null) {
if (cursor.moveToFirst()) {
value = cursor.getSomething();
}
cursor.close();
}
// multiple columns
Cursor cursor = db.query(...);
if (cursor != null) {
while (cursor.moveToNext()) {
values.add(cursor.getSomething());
}
cursor.close();
}
In case people are still looking:
Instead of searching for "ContactNumber" try searching for Phone.NUMBER. The tutorial has the code with more details: http://developer.android.com/training/basics/intents/result.html
try to uninstall the app and then again test it... actually the sqlite db is created only once when the app is first install... so if you think your logic is current then reinstalling the app will do the trick for you. !!!!
I have some trouble with a SQLite database with 1 table and 2 columns, column_id and word. I extended SQLiteAssetHelper as MyDatabase and made a constructor:
public MyDatabase(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
I need to check whether some string is in the database (in column word). I tried to modify the code from answer provided by Benjamin and dipali, but I used SQLiteAssetHelper and I can't get it to work. The method that I have in mind receives the string to search for as a parameter and returns a boolean if string is in the database.
public boolean someMethod(String s)
In addition, I tried to put the check on a background thread with AsyncTask because I have 60 strings to check.
TABLE_NAME and COLUMN_WORD should be self-explanatory.
public boolean someMethod(String s) {
SQLiteDatabase db = getReadableDatabase();
String[] columns = new String[] {COLUMN_WORD};
String where = COLUMN_WORD + " = ?";
String[] whereArgs = new String[] {s};
// select column_word from table where column_word = 's' limit 1;
Cursor cursor = db.query(TABLE_NAME, columns, where, whereArgs, null, null, null, "1");
if (cursor.moveToFirst()) {
return true; // a row was found
}
return false; // no row was found
}
You can do this in the background, but I don't think for a query like this it's even necessary.
EDIT
There are some improvements that should be made to the above for the sake of correctness. For one thing, the Cursor should be closed since it is no longer being used. A try-finally block will ensure this:
Cursor cursor = db.query(...);
try {
return cursor.moveToFirst();
} finally {
cursor.close();
}
However, this method doesn't need to obtain a whole `Cursor. You can write it as follows and it should be more performant:
public boolean someMethod(String s) {
SQLiteDatabase db = getReadableDatabase();
String sql = "select count(*) from " + TABLE_NAME + " where "
+ COLUMN_WORD + " = " + DatabaseUtils.sqlEscapeString(s);
SQLiteStatement statement = db.compileStatement(sql);
try {
return statement.simpleQueryForLong() > 0;
} finally {
statement.close();
}
}
You could add a catch block and return false if you think it's possible (and valid) to encounter certain exceptions like SQLiteDoneException. Also note the use of DatabaseUtils.sqlEscapeString() because s is now concatenated directly into the query string and thus we should be wary of SQL injection. (If you can guarantee that s is not malicious by the time it gets passed in as the method argument, then you could theoretically skip this, but I wouldn't.)
because of possible data leaks best solution via cursor:
Cursor cursor = null;
try {
cursor = .... some query (raw or not your choice)
return cursor.moveToNext();
} finally {
if (cursor != null) {
cursor.close();
}
}
1) From API KITKAT u can use resources try()
try (cursor = ...some query)
2) if u query against VARCHAR TYPE use '...' eg. COLUMN_NAME='string_to_search'
3) dont use moveToFirst() is used when you need to start iterating from beggining
4) avoid getCount() is expensive - it iterates over many records to count them. It doesn't return a stored variable. There may be some caching on a second call, but the first call doesn't know the answer until it is counted.
I am just trying to search for the data in multiple table.If the where condition data is not present in first table(tab1) then it has to search in the second table(tab2) but I am getting the exception showing that
Cursor Index Out of Bounds Exception: Index -1 requested with size 0
Here is my code
SQLiteDatabase db=openOrCreateDatabase("train",SQLiteDatabase.CREATE_IF_NECESSARY, null);
Cursor c1;
String[] table={"tab1","tab2","tab3","tab4"};
int i=0;
do {
c1 = db.rawQuery("select * from '"+table[i]+"' where name='Triplicane'", null);
i++;
} while(c1 == null);
int id1=c1.getInt(0);
String nam1=c1.getString(1);
Toast.makeText(fare.this,"ID no:"+id1, Toast.LENGTH_LONG).show();
Toast.makeText(fare.this,"name"+nam1, Toast.LENGTH_LONG).show();
So from the beginning. Implicitly, each Cursor is positioned before first row so if you want to work with it you need to call
cursor.moveToFirst()
that moves Cursor to first row if is not empty and then is ready for work. If Cursor is empty simply it returns false. So how i mentioned now this method is very handy indicator whether your Cursor is valid or not.
And as my recommendation i suggest you to change your code because i think is broken and it sounds like "spaghetti code"
Cursor c = null;
String[] tables = {"tab1", "tab2", "tab3", "tab4"};
for (String table: tables) {
String query = "select * from '" + table + "' where name = 'Triplicane'";
c = db.rawQuery(query, null);
if (c != null) {
if (c.moveToFirst()) { // if Cursor is not empty
int id = c.getInt(0);
String name = c.getString(1);
Toast.makeText(fare.this, "ID: " + id, Toast.LENGTH_LONG).show();
Toast.makeText(fare.this, "Name: " + name, Toast.LENGTH_LONG).show();
}
else {
// Cursor is empty
}
}
else {
// Cursor is null
}
}
Notes:
Now i want to tell you some suggestions:
An usage of parametrized statements is very good practise so in a
future if you will work with statements, use placeholders in them. Then your statements becomes more human-readable, safer(SQL Injection) and faster.
It's also a very good practise to create static final fields that will hold
your column names, table names etc. and to use
getColumnIndex(<columnName>) method to avoid "typo errors" which are looking for very bad.
Your Cursor flag to empty row , On Sqlite cursor pointed to row number -1 ,
then if you use c.moveNext() or c.moveToFirst() you'll be able to read rows "row by row "
write cursor.movetoFirst() before getting data from cursor.
Now I want to access an entire column from database and then compare it with some text that I have stored...but I am getting no idea on how to do that..So can someone please help me with this...
Entire column? You mean all the values for a given column accross all records?
You should iterate the ResultSet obtained and start comparing the values (for example - if you iterate using "rs" object of ResultSet, you should compare:
String valueFromDB = rs.getString("myColumn");
String someTextStored = .... //the text being stored
if (valueFromDB != null) {
if (someTextStored.equals(valueFromDB) {
//Comparison succeeded - implement some logic here for handling success
}
}
And the above code should be inside a loop code that iterates over the ResultSet and
uses the "next" method to obtain the next record.
Hope this helps you
public ArrayList<String> getValues(){
Cursor cursor = null;
SQLiteDatabase db = getReadableDatabase();
Log.v("done","getting rows ");
cursor = db.rawQuery("SELECT YourColumnName FROM "+TABLE_NAME, null);
if(!cursor.moveToFirst()){
}
else{
do {
list_values.add(cursor.getString(0));
} while (cursor.moveToNext());
}
db.close();
cursor.close();
return list_values;
}
Now you are having all the values of a particular column you can compare it from this array list.
So I'm working on a game for android and I'm currently stuck at the 'load savegame' button in the main menu.
This button calls methods that read data from the database and write it into a resource class from which on this data will be accessed.
The problem is: I want to disable the load button if there are no rows in the tables, which means that no savegame exists.
To do this I used the following method:
public boolean checkForTables(){
boolean hasTables;
String[] column = new String[1];
column[0] = "Position";
Cursor cursor;
cursor = db.query("itemtable", column, null, null, null, null, null);
if(cursor.isNull(0) == true){
hasTables=false;
}else{
hasTables=true;
}
return hasTables;
As you can see it starts a query on one of the database tables and checks if the 0-column, which is the only one that should be in this cursor, is null. ATM I can't check logcat results on this call because I seem to have some problems with it, but it seems that the query throws an exception because the table is empty.
Any idea to check the tables for rows?
____________________EDIT______________
NOTE: I checked the database and it sure is empty
Okay I used a rawQuery on the table but the approach with count-statement produced an error, so I'm using
public boolean checkForTables(){
boolean hasTables;
Cursor cursor = db.rawQuery("SELECT * FROM playertable", null);
if(cursor.getCount() == 0){
hasTables=false;
if(cursor.getCount() > 0){
hasTables=true;
}
cursor.close();
return hasTables;
}
I'm using this method to decide whether or not to disable the loadGame-button which looks like this:
loadGame = (ImageButton) findViewById(R.id.loadButton);
loadGame.setEnabled(databaseAccess.checkForTables());
loadGame.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
databaseAccess.loadPlayer();
databaseAccess.loadItems();
databaseAccess.dropTables();
}
});
So if checkForTables gets a rowcount of != 0 it will return true and therefore enable the Button, or disable it if rowcount = 0
Amusingly, although the tables are empty, checkForTables() returns true because getCount() seems to return a != 0 value - I just don't get it.
Perform a query such as select count(*) from itemtable. This query will yield you a single integer result, containing the number of rows in that table.
For example:
Cursor cursor = db.rawQuery("SELECT count(*) FROM itemtable");
if (cursor.getInt(0) > 0) ... // there are rows in the table
-------------------------------------------------------------------------------------
Please note that the following edit was attempted by #PareshDudhat but was rejected by reviewers. I have not kept up with Android since this answer was posted, but a very brief bit of research suggests the edit (at least the change to how rawQuery() is called, I didn't inspect the moveToFirst() but #k2col's comment suggests it is required now as well) has merit.
Cursor cursor = db.rawQuery("SELECT count(*) FROM itemtable",null);
cursor.moveToFirst();
if (cursor.getInt(0) > 0) ... // there are rows in the table
What mah says will work. Another approach you could use in your current function is:
hasTables = cursor.moveToFirst());
Note that this approach is probably only better to use if you plan on using the results of the query if hasTables is in fact true.
Also, don't forget to close your cursor when you are done with it!
EDIT
I don't know if this is your problem but in your edit you are querying for all items from the playerTable instead of the itemTable as you did in the pre-edit. Is that your problem?
cursor.getCount()
return the number of rows in database table.
and then try
Toast.makeText(this,""+cursor.getCount(),Toast.LENGTHLONG).show();
and it will give you no of rows in database table
The accepted answer put me on the right track, but didn't compile because rawQuery's method signature has changed and the cursor wasn't advanced to the first row before being read.
Here's my solution which includes error handling and closes the cursor:
public static boolean isEmpty() {
boolean isEmpty;
Cursor cursor = null;
try {
cursor = db.rawQuery("SELECT count(*) FROM itemtable", null);
if (cursor.moveToFirst()) {
isEmpty = cursor.getInt(0) == 0;
} else {
// Error handling here
}
} catch (SQLException e) {
// Error handling here
} finally {
cursor.close();
}
return isEmpty;
}