How do I return the number of rows of a table according to a search criteria in Web SQL? - html

Question

I have created a database called todo with table name todo having fields like title,date etc. The table is empty right now.
I have defined a function which takes title as parameter and check whether table contains that title or not.
It should return the number of rows.
GetTitle function:
todo.webdb.GetTitle = function(title) {
var db = todo.webdb.db;
db.transaction(function(tx){
tx.executeSql("SELECT title FROM todo WHERE title=?", [title],
loadTitle,
todo.webdb.onError);
});
}
loadTitle Function:
function loadTitle(tx, rs) {
return rs.rows.length;
}
GetTitle Function is called:
row=todo.webdb.GetTitle("Hello");
alert(row);
I get alert 'undefined' it should return 0
I am confused right now how to resolve this issue.

Answer 1

I think the transactions are asynchronous, so you need to callback function to receive the value.
todo.webdb.GetTitle = function(title, callback) {
var db = todo.webdb.db;
db.transaction(function(tx){
tx.executeSql("SELECT title FROM todo WHERE title=?", [title],
(function loadTitle(tx, rs){
callback( rs.rows.length );
}),
todo.webdb.onError);
});
}
todo.webdb.GetTitle( "Hello", function(count){
alert( "count = " + count );
});
Here's an excellent tutorial for more information.
http://blog.darkcrimson.com/2010/05/local-databases/
Update
Don't make functions inside a loop for this main reason.
Both i and title are referencing a value created out of local scope.
So the last value of assigned to both i and title will be displayed.
for (i = 0; i < itemcount; i++) {
alert('i outside if:' + i);
var title = x[i].getElementsByTagName("title")[0].childNodes[0].nodeValue;
todo.webdb.GetTitle( title, function (count) {
if (!count) {
alert('i inside if:' + i);
alert( title );
}
});
}
Fix:
Generate a function that has the values locked in a closure.
var createTitleCallBack = function( i, title ){
return function (count) {
if (!count) {
alert('i inside if:' + i);
alert( title );
}
};
};
for (i = 0; i < itemcount; i++) {
alert('i outside if:' + i);
var title = x[i].getElementsByTagName("title")[0].childNodes[0].nodeValue;
todo.webdb.GetTitle( title, createTitleCallBack( i, title ) );
}