How do I rewrite a single element in a .phtml file?

Question

In my custom module I want to rewrite parts of several .phtml files. For example, in app/design/frontend/base/default/template/bundle/catalog/product/price.phtml, I want to rewrite <div class="price-box">.

Please note: I do not want to override the entire file, just this one div.

Given that when I override blocks and models I can rewrite individual functions of specific core classes by simply extending the class, I would expect that I could also rewrite a single element of a .phtml file by using SimpleXMLElement::xpath to use xpath to manipulate the XML of the .phtml file itself. That way I could make my module automatically detect if the parts of the .phtml file it's overriding have been changed (say, by an update, or by the installation of another module) and automatically disable my module and warn the user should this occur.

How would I go about approaching doing this? It seems that every guide I can find to how to override a .phtml file takes the rather draconian, brutal, and ugly approach of having a separate folder outside the module's main folder (/app/code/{codePool}/{nameSpace}/{moduleName}), instead putting it into /app/design/frontend/{rest of the path}. This seems very non-ideal because not only does it mean the module is not self-contained in a single directory (for everything but the module's main XML file) but also it requires overriding the entire .phtml file (not just the part you are changing) and it can lead to major problems down the road should there be updates to the file you're overriding (since your module has no way to detect those changes and overrides the entire file).

I just want to find a better way. Is there one?

EDIT:

Clarification: lets say I have a .phtml file with a single div. In that div there are appx. 210 lines of code (some are HTML lines, some are PHP lines). What I want to do is inject 160 new lines of code (some HTML, some PHP) prior to the existing lines that are inside that div, before it gets executed by the PHP interpreter.

Answer 1

This seems very non-ideal because not only does it mean the module is not self-contained in a single directory ...

What is "non-ideal" about it other than your lack of taste for it? Why does it all have to be in a single directory? Some parts go in design, some parts go in a code pool. If you know what should go where, it is not really an issue most of the time.

... but also it requires overriding the entire .phtml file (not just the part you are changing) ...

There are a number of ways to change content. The approach that it sounds like you're taking is one of "let's do this in a way that nobody would suspect instead of using the built-in tools Magento provides us".

You could, instead, design your own block that does what you want it to do and use your module's layout update XML to remove the old one and add your new one. Nobody says you must rewrite a template.

Please note: I do not want to override the entire file, just this one div.

But, that's the only div in that template.

... and it can lead to major problems down the road should there be updates to the file you're overriding (since your module has no way to detect those changes and overrides the entire file).

Again, nobody says you have to override a file, and even then, if you do there is a package/design system for a reason.

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EDIT

If the condition being checked is an admin config value, you can also use the ifconfig attribute to adjust the template being loaded, see: Conditionally show/hide blocks in layout XML

Answer 2

You can use event core_block_abstract_to_html_after, get the block HTML and modify it with regular expression or as XML via DOM / simplexml. No rewrites.

Answer 3

I came across your question when about to ask exactly the same thing myself. It feels as though overriding a whole phtml file is like using a hammer when what you really want is a scalpel. By reading the answers you've received I have convinced myself why things have to be this way.

The big difference between rewriting class methods and the code within a phtml file is what you can sensibly reference. The structure of a class is simple and more importantly predictable, it has methods and properties, nothing else, so its easy to refer to a method and swap it out. What elements would you suggest referencing in a phtml file so that you could inject your code; the div's, span's, fieldset's, line numbers? There are just no natural candidates.

Manipulating the phtml via a DOM would be great, but the phtml files are not well formed XML; try loading one with simpleXML and see how far you get! I think that to be able to manipulate the phtml files, you'd require a manipulator which could also interpret PHP.

Another way of looking at this problem is to reverse your argument. You hold up the ability to override individual class methods as good design, but you don't go on to grumble that its not possible to override individual lines within a class method. All the reasons you gave why its bad you can't modify individual lines within a phtml file apply just as strongly as to why can't modify lines within a class method.

It all boils down to what you can reference. Its easy to reference complete files and methods within a file, but it would be very difficult to reference elements within a phtml file.

I agree that finding overrides during an update is a pain. I use the following algorithm for dealing with this:

1. Generate a list of all core files which have been overridden - look in app/design/mytheme, app/code/local etc
2. Compare this list with a list of all files changed by the patch
3. Merge the changes into the overrides

I've semi automated the first two steps with a small PHP script.