Return a COUNT from a WebSQL query in a javaScript function

Question

I want to return the number of rows in a particular table in a database in WebSQL inside a javascript function. Below is my code.

function getCustomerCount(){    
    var count = 0;  
    db.transaction(function(tx) {   
    tx.executeSql('SELECT * FROM contacts', [], function(tx, results) {
             count = results.rows.length;   
        });
    });
    return count;
}

I am new to WebSQL and rather unfamiliar with javascript also.
Any suggestions?

use the SQL count query `SELECT COUNT(*) FROM contacts` – TheGr8_Nik Oct 02 '14 at 08:17 — TheGr8_Nik, Oct 02 '14 at 08:17

TheGr8_Nik · Answer 1 · 2014-10-02T08:30:19.277

2

You can't do this:

function getCustomerCount(){    
    var count = 0;  
    db.transaction(function(tx) {   
    tx.executeSql('SELECT * FROM contacts', [], function(tx, results) {
             // this function is called when the executeSql is ended
             count = results.rows.length;   
        });
    });
    // This returns always 0!
    return count;
}

You have to use callbacks like so:

function getCustomerCount( callback ){    
    var count = 0;  
    db.transaction(function(tx) {   
    tx.executeSql('SELECT * FROM contacts', [], function(tx, results) {
             // this function is called when the executeSql is ended
             count = results.rows.length;
             callback( count );   // <-- call the callback when is done   
        });
    });
}

And use it like:

getCustomerCount( function( count ) {
    // do what you want with the count
    console.log( 'The number of rows is: '+ count );
});

edited Oct 02 '14 at 08:30

answered Oct 02 '14 at 08:24

TheGr8_Nik

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Perhaps it's better to remove the return statement in the second example – slebetman Oct 02 '14 at 08:26
The thing is I want to use that count in another location so that I want to return the value. Anything that can be done to return the count? – vidulaJ Oct 02 '14 at 08:37
it's the easier way to retrieve that number – TheGr8_Nik Oct 02 '14 at 08:42
Thanx for the time and support; that I wanted to return a value and use it somewhere I will go with jQuery method. – vidulaJ Oct 02 '14 at 09:02
@Droidy - you can simply call your `exampleThatUsesCount(count);` method instead of the `console.log()` – TheGr8_Nik Oct 02 '14 at 09:19

score 1 · Accepted Answer · answered Oct 02 '14 at 08:50

Another way is to use promises, here is an example with the Jquery deferred object

function getCustomerCount() {
    //setup the deferred object
    var defer = $.Deferred();
    var count = 0;
    db.transaction(function(tx) {
        tx.executeSql('SELECT * FROM contacts', [], function(tx, results) {
            //resolve the promise passing the count data
            defer.resolve(results.rows.length);
        });
    });

    //return a promise
    return defer.promise();
}

var countPromise = getCustomerCount();

//when the promise is resolved do something with the data
$.when(countPromise).done(function(count) {
    //now use count, could be you call another function that needs to use count,
    exampleThatUsesCount(count);
   //or assign it to another variable, or trigger an event that someone else in you app is    listening for
});


function exampleThatUsesCount(count) {
    //do something that uses count here
}

Why use this method? you are adding complexity that isn't needed! — TheGr8_Nik, Oct 02 '14 at 09:18
I was just showing another example of how to handle async processes don't see that being worthy of a down vote. Personally I like promises as I find it easier for my code to grow. — Quince, Oct 02 '14 at 09:39

Return a COUNT from a WebSQL query in a javaScript function

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