Joomla! Documentation™

Joomla! 

3.x

Tutorial

Developing an MVC Component

Articles in This Series

1. Introduction
2. Developing a Basic Component
3. Adding a View to the Site Part
4. Adding a Menu Type to the Site Part
5. Adding a Model to the Site Part
6. Adding a Variable Request in the Menu Type
7. Using the Database
8. Basic Backend
9. Adding Language Management
10. Adding Backend Actions
11. Adding Decorations to the Backend
12. Adding Verifications
13. Adding Categories
14. Adding Configuration
15. Adding ACL
16. Adding an Install/Uninstall/Update Script File
17. Adding a Frontend Form
18. Adding an Image
19. Adding a Map
20. Adding AJAX
21. Adding an Alias
22. Using the Language Filter Facility
23. Adding a Modal
24. Adding Associations
25. Adding Checkout
26. Adding Ordering
27. Adding Levels
28. Adding Versioning
29. Adding Tags
30. Adding Access
31. Adding a Batch Process
32. Adding Cache
33. Adding a Feed
34. Adding an Update Server
35. Adding Custom Fields
36. Upgrading to Joomla4

This is a multiple-article series of tutorials on how to develop a Model-View-Controller Component for Joomla! Version.

Begin with the Introduction, and navigate the articles in this series by using the navigation button at the bottom or the box to the right (the Articles in this series).

This tutorial is part of the Developing an MVC Component for Joomla! 3.2 tutorial. You are encouraged to read the previous parts of the tutorial before reading this.

In this step we add checkout capability to our component.

Introduction

Checkout capability avoids the unexpected results which can arise when 2 users edit the same record simultaneously. It provides a record-locking capability which means that only 1 user can edit the record at the one time. You might want to have this capability in your component if you have many users updating your component's database records and have a significant probably of 2 users updating the same record simultaneously. This might arise if you allow updates from the front end of your site, although in this tutorial step we just consider the back end; the work required on the front end to support checkout would be similar.

A number of core Joomla components, including com_content, support checkout, so we will mirror that functionality in our helloworld component.

Functionality

We want to support the following aspects

1. checking out a record when a user accesses it for editing
2. checking in a record whenever the user has finished editing (either by typing Save or Cancel)
3. preventing other users from editing the record when it's checked out
4. displaying on our helloworlds view the records which are locked (using the little padlock symbol)
5. allowing an authorised user to override the checkout and checkin a record manually

Approach

As usual, Joomla provides a lot of core functionality which we can reuse, provide we align with how the standard Joomla approach.

To our database record we need to add 2 fields

1. checked_out – which holds the id of the user who has checked out the record
2. checked_out_time – a date/timestamp field which records when the record was checked out

The very presence of these fields in our database record switches on the checkout functionality in the JTable class, and as checkin and checkout functionality is already in the Admin and Form Controllers/Model (which ours inherit from), there's no need to do anything else to enable the checkout functionality working for editing helloworld records.

(If you're adding this sort of control you may wish to add also "modified" and "modified_by" fields to capture the user who last modified the record, and when that occurred. Joomla automatically populates these fields for us as well.)

All that we are left to handle by ourselves is the display in our helloworlds view, and for that we need to do the following:

1. include the checked_out and checked_out_time fields in our select query in the model
2. display the little padlock symbol against records which are checked out, and enable clicking on it based on whether the user is authorised to checkin records which are checked out.
3. currently a user can click on a record to edit it – we'll disable this if the record is checked out, and the user doesn't have checkin capability
4. include a Checkin button in the toolbar.