CODEWITHSUNDEEP
javascriptsqlite
lukeshek
lukeshek

Reputation: 978

JS function to count rows in SQLite table

I'm trying to make a JS function that counts rows in an SQLite table.

function countRows(){
    db.transaction(function (tx){
        tx.executeSql('SELECT id FROM table', [], function (tx, results) {
            var len = results.rows.length;
            alert(len);
        });
    });
}

The above code displays an alert with numbers of rows in the table. However, I'd like to make a function that would return the number instead of showing the alert box.

I tried:

function countRows(){
    db.transaction(function (tx){
        tx.executeSql('SELECT id FROM table', [], function (tx, results) {
            var len = results.rows.length;
            return len;
        });
    });
}

And then:

var number = countRows();
alert (number); // returns "undefined"

The above example returns "undefined", whereas a parallel example works fine:

function count(){
    return 3;
}
var number = count();
alert (number); // returns 3

I want to assign the number to a variable, so I could then make another sql query, count rows in another table, and compare the two results.

In PHP this would be:

$sql1 = mysql_query('SELECT COUNT(*) FROM table1');
$rows1 = mysql_result($sql1, 0);
$sql2 = mysql_query('SELECT COUNT(*) FROM table2');
$rows2 = mysql_result($sql2, 0);
if ($row1>$row2){}

Upvotes: 1

Views: 7774

Answers (2)

Ivan
Ivan

Reputation: 2262

db.transaction is asynchronous. returning value isn't assigned to any variable in code above. Solution is to pass callback or create custom event, which is almost the same.

Something like this:

function countRows(cb){
    db.transaction(function (tx){
        tx.executeSql('SELECT id FROM table', [], function (tx, results) {
            var len = results.rows.length;
            cb.call(this, len);
        });
    });
}

countRows(function (num) {alert(num)});

Upvotes: 2

Daniel A. White
Daniel A. White

Reputation: 190947

You would be served much better by changing your query.

SELECT COUNT(ID) FROM table

Plus, its an async call so that the call return is returning the callback function. You should pass your own callback function.

function countRows(callback){
    db.transaction(function (tx){
        tx.executeSql('SELECT id FROM table', [], function (tx, results) {
            var len = results.rows.length;
            callback(len);
        });
    });
}

Upvotes: 4

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