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Opencart Modification System Related Questions

I have been using opencart since a short time. But I know nothing about Vqmod, Ocmod and third part extensions. I have few questions about them. I have searched Goolge and forum but did not find a solution, so I came to you for help. I would be greately thankful if someone guides me.

  1. Does Ocmod or Vqmod installation makes any changes to core files of oencart

  2. Does Ocmod or Vqmod installation is necessary to avoid changes in core files, if we install anyother third party extensions

  3. If we install a third party extension without ocmod.zip or vqmod.zip file extension manually, does it make changes to core files

  4. Has Ocmod and Vqmod been developed by opencart itself or it is developed by independent developers and opencart community.

  5. Does different ocmods or vqmods are needed to make changes in different files for example theme, controller and catalog or same ocmod or vqmod can perform all the tasks

  6. Where to download standard ocmod or vqmod to make changes in opencart without effecting the core files. I went to opencart market place. I found ocmod manager, ocmod editor, ocmod downloader. But I did not find ocmod or vqmod extension to make changes in opencart files for example theme without effecting core files.

Solution
    1. OCMOD or VQMOD installation doesn't make any changes to core files of OpenCart. That's the main purpose of these two systems. To make changes without making changes. These systems are creating cached copies of the core files with changes, which were implemented by OCMOD or VQMOD files.
    2. Third party extensions sometimes doesn't need any core changes. They may only add new files and new tables to database. BUT! When third party extensions need to overwrite core files - they have to use OCMOD or VQMOD to do it. Sometimes they have to change core files, but you should be careful with this kind of extensions. That may cause conflicts between other extensions, which are calling the same file with OCMOD or VQMOD.
    3. If you install a third party extension without ocmod.zip or vqmod.zip file extension manually, your FTP client will ask you, if you want to rewrite some specific files, if there are any files to rewrite, so you can make backups of those files or to analyse what changes has been made in new files. In other cases you will only paste new files without rewriting anything.
    4. VQMOD has been developed somewhere in OpenCart 1.5 version. It's a standalone extension developed outside of the main OpenCart core. Have to be installed manual. Since OpenCart version 2 - OCMOD was implemented. It has been developed in the image and likeness of VQMOD, but with several differences. And OCMOD is native to OpenCart and fully integrated.
    5. Using OCMOD or VQMOD you can make changes only in .php, .tpl and .twig files, you can't make any changes in .css or .js, only by adding new files.
    6. First of all. Forget about VQMOD, it's outdated. OCMOD is native and supported by 95% of extensions. And those extensions who doesn't support OCMOD - are although mostly outdated. OCMOD file is basically a bunch of statements of where to find some code and what to do with it (replace it or add something before/after it). And the result is cached core file with changes. You can fine them generally in /system/storage/modification/. If you installed new OCMOD file - you should clear cache to implement changes. More about OCMOD cache cleaning.

    Using both OCMOD or VQMOD - is not the best experience and may cause conflicts and errors. It its possible to use them together, but you will have to be careful and patient. Just use OCMOD.

    More about OCMOD installation and file structure.