PHP

When creating functions in PHP it is possible to provide default parameters so that when a parameter is not passed to the function it is still available within the function with a pre-defined value. These default values can also be called optional parameters because they don't need to be passed to the function. I have seen this sort of code being used incorrectly quite often recently so I thought I would go over it in a post.

Creating a default parameter in a function is very simple and is quite like normal variable assignment. The following function has a single parameter that is set to 1 if it is not passed when calling the function.

function testFunction($a = 1)
{
    return $a;
}

It is usual when writing a list of items to separate each item with a comma, except the last two items, which are separated with the word "and". I recently needed to implement a function that took a string and converted it into a list of this type so I thought I would expand on it and post it here.

The function takes a single parameter, which can either be an array or a comma separated string. If an array is passed to the function then it is converted into a comma separated string and then passed onto the next part in the function. The function then removes any trailing commas, any commas that have nothing in between them and then makes sure that each comma has a single space after it. The final step is to replace the last comma with the word "and". Once the manipulation is complete then the resulting string is returned. If the string (after removing any trailing commas) doesn't contain any commas then it is simply returned.

Overloading in PHP describes the way in which properties and methods of an object can be dynamically created or accessed without having to define them first. Traditionally, the word overloading in programming is used to describe accessing object methods with the same name but with different parameters. It is not possible to do this in PHP as it will complain about methods having the same name, so the term describes calling a method or accessing a property that hasn't previously been set or is out of scope. In object orientated terms this means that the method or property is private.

Object Property Overloading

Property overloading allows you to access the property of an object through a method without having to write them first. It can also be used to access any properties that are inaccessible. There are two basic property overloading methods available, these are __set() and __get(), both contain a double underscore (_) in their name.

The other day I needed to copy a Drupal project from my source folder to another folder, so rather than manually copy the files I decided to create a Phing script that would do it for me in one go. This Phing script will export your Drupal project into another directory, change the database credentials and create zip and tar files of the project. The first thing to do is create a properties, here is the contents of that file.

When you run a phing script it will print things out to the console. These messages are either system messages (eg. BUILD STARTED) or echo messages that you have put into your build.xml file. All of this output is controlled and created by a logger file. The default logger is called (unsurprisingly) DefaultLogger and will be used as a default. There are a few different types of logger available, all of which can be found in the listener folder in your PEAR\phing directory.

To select a different logger script to be used just use the -logger flag in your phing call. To specify the DefaultLogger use the following:

phing -logger phing.listener.DefaultLogger

To specify an XML logger that will create an XML document of the phing events that occurred in the current working directory use the XmlLogger logger.

If you have been following the last four posts you should now have an application that will allow you to view and edit PDF metadata, extract the document contents for search indexing, and allow users to search that index.

The one final thing to do is to sort out what happens when any PDF metadata is changed. At the moment the application will allow us to change the metadata as much as we like, but these changes will not be replicated in our search index. In order to do this we have to fully re-index everything. This is obviously the wrong way to go about things, and the solution is quite simple. All we need to do is up the file controllers/PdfController.php and change the editmetaAction() method so that when the PDF metadata is saved, the search index is updated. Add the following code to the editmetaAction() method, just before the redirect.

Last time we had indexed our PDF documents and were ready to add a search form to our application. Adding search requires two things, the form to enter the search terms into and an action to control what happens when the form is submitted.

The easiest task is to set up the search view, create the view file search.phtml (in views/scripts/search/) and add the following code. This is just a basic form with a single text input. Note the addition of the queryString parameter, this will allow us to print out the last searched for value in the search box, which is good usability practice.

Last time we had reached the stage where we had PDF meta data and the extracted contents of PDF documents ready to be fed into our search indexing classes so that we can search them.

The first thing that is needed is a couple of configuration options to be set up. This will control where our Lucene index and the PDF files to be indexed will be kept. Add the following options to your configuration files (called application.ini if you used Zend Tool to create your applcation).

luceneIndex = \path\to\lucene\index
filesDirectory = \path\to\pdf\files\

Last time we looked at viewing and saving meta data to PDF documents using Zend Framework. The next step before we try to index them with Zend Lucene is to extract the data out of the documents themselves. I should note here that we can't extract the data perfectly from every PDF document, we certainly can't extract any images or tables from the PDF into any recognisable text. There is a little issue with extracting the text because we are essentially looking at compressed data. The text isn't saved into the document, it is rendered into the document using a font. So what we need to do is extract this data into some format the Lucene can tokenize. Because we are just getting the text out of the document for our search index we can take a few short-cuts in order to get as much textual data out of the document as possible. All of this data might not be fully readable and we will definitely loose any formatting and images, but for the purposes we are using it for we don't really need it. The idea is that we can retrieve as much relevant and indexable content for Zend Lucene to tokenize. Also, it is not possible to extract the data out of encrypted PDF documents.

Zend Lucene is a powerful search engine, but it does take a bit of setting up to get it working properly. One thing that I have had trouble getting up and running in the past is indexing and searching PDF documents. The difficulty here is that it isn't immediately apparent how you can index the contents of a PDF document with ease. I came across a couple of functions you can try out, but even if that doesn't work it is possible to create and edit PDF meta data using the Zend_Pdf library. Because there is a lot to cover on this subject I thought I would create a blog post in multiple parts. For this post I will be looking at how to add and edit this meta data. This meta data can be used to classify your PDF documents and allow you to index them and provide a decent search solution using Zend Lucene.