return instance of database in javascript - html

Question

Hi There best collegue,
i'm doing some experience with Object Oriented Javascript in combination with Mootools and creating a todolist for exercise. i've the following issue.
i've a class called database and looks as followd
var Database = new Class({
initialize:function(db){
this.db = db;
this.prepareDatabase();
this.createTable();
},
/*
* Creates the todo database
* #return {object Database}
* alDone ensures that the function will be called once, because we only want one database
* with the name 'Todo'
*/
prepareDatabase:function(){
var alDone = false;
if(!alDone){
var dbSize = 5 * 1024 * 1024; // 5MB
this.db = openDatabase("Todo", "1.0", "Todo manager", dbSize);
}else{
alDone = true;
}
},
/*
* Creates table 'todo'
* alDone ensures that the function will be called once, because we only want one table
* with the name 'todo'
*/
createTable:function(){
var alDone = false;
if(!alDone){
this.db.transaction(function(tx){
tx.executeSql("CREATE TABLE IF NOT EXISTS todo(ID INTEGER PRIMARY KEY ASC, title TEXT, description TEXT, isDone INTEGER, date DATETIME)", [])
});
}else{
alDone = true;
console.log("functie createTable is al aangeroepen");
}
},
});
and i've created a class todo. the goal I want to achieve is to create a instance of the db and call this in a method in the todolist class. I would be gratefull if someone can help me with this issue.
Tnx in advance.
my todolist class looks like below.
var Todo = new Class(
{
initialize: function(title,description,isDone,date){
this.title = title;
this.description = description;
this.isDone = isDone;
this.date = date;
},
getTitle:function()
{
return this.title;
},
getDescription:function()
{
return this.description;
},
getIsDone:function()
{
return this.isDone;
},
setIsDone:function(value)
{
this.isDone = value;
},
});

Answer 1

I did not understand what you are trying to do here but here is some errors you have:
In class Database you get db param in the constructor and set it to a class property name db: this.db = db; - Then you call prepareDatabase which override that this.db by setting it to openDatabase("Todo", "1.0", "Todo manager", dbSize); - so why sends the constructor db param if you override it in the next operation ?
you want the functions prepareDatabase and createTable will be called once so you set a variable alDone - but this variable is local to the function so in each call to one of this functions alDone will always be false and get executed - what I guess you want is set a class variable that each call to the function wil "remember" it's state so you can do something like this:
end List item (this is stackoverflow bug :))
prepareDatabase:function(){
if(!this.alDone){
this.alDone = true;
var dbSize = 5 * 1024 * 1024; // 5MB
this.db = openDatabase("Todo", "1.0", "Todo manager", dbSize);
}
},
Then again you can't call this.alDone twice so you need to change the name in the other function (createTable)
Continue:
If you want to make your db class "global" (the right term is static) then don't use mootools Class - use regular js objects: (you can use mootools inside of course)
var Database = {
init:function(db){
this.db = db;
this.prepareDatabase();
this.createTable();
},
prepareDatabase:function(){
if(!this.donePrepare){
this.donePrepare = true;
var dbSize = 5 * 1024 * 1024; // 5MB
this.db = openDatabase("Todo", "1.0", "Todo manager", dbSize);
}
},
createTable:function(){
if(!this.doneCreate){
this.doneCreate = true;
this.db.transaction(function(tx){
tx.executeSql("CREATE TABLE IF NOT EXISTS todo(ID INTEGER PRIMARY KEY ASC, title TEXT, description TEXT, isDone INTEGER, date DATETIME)", [])
});
}else{
console.log("functie createTable is al aangeroepen");
}
}
};
Then you can call it from everywhere like this:
Database.init();