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?
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 );
});
exampleThatUsesCount(count); method instead of the console.log()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
}
SELECT COUNT(*) FROM contacts