PHP Master | Using YAML in Your PHP Projects

YAML: Data serialization format to improve the efficiency of PHP projects

The test device, configuration file and log file all need to take into account both human and machine readability. YAML (YAML Ain’t Markup Language) is a simpler data serialization format than XML, and is popular among software developers for its legibility. YAML files simply contain text data files written according to YAML syntax rules, usually with the extension .yml. This article will introduce the basics of YAML and how to integrate the PHP YAML parser in your PHP project.

Key points:

• YAML is a simpler data serialization format than XML, and is popular among developers for its legibility. It is commonly used for testing devices, configuration files, and log files, and can be integrated into PHP projects through the PHP YAML parser.
• Understanding YAML syntax is crucial for PHP developers. YAML represents enumerating arrays (sequences in YAML terms) and associative arrays (mappings) similar to PHP. Indentation in YAML must use spaces, not tabs.
• YAML should not be considered a replacement for XML. Both have advantages: YAML is simpler, easier to write and read, and does not require a tree structure with a single parent node. XML, on the other hand, has more built-in PHP support and is widely recognized for communication between applications, and its tags can have attributes to provide more information about the data contained.
• Selecting a PHP YAML parser depends on the needs of the project. PHP's YAML parser can be used as a PECL extension, but there are also parsers written in pure PHP, such as the Symfony 1.4 YAML component. Integrating PHP YAML parser into a PHP project should be done with caution, and wrappers and test suites are required to ensure functionality is correct.

Detailed explanation of YAML grammar

YAML supports advanced features such as references and custom data types, but as a PHP developer, you will pay attention to how YAML represents enumerated arrays (sequences in YAML terms) and associative arrays (mappings). The following is the representation of enumerated arrays in YAML:

- 2
- "William O'Neil"
- false

Each element of the array appears after hyphen and spaces. The syntax for representing values ​​is similar to PHP (reference strings, etc.). The above content is equivalent to the following PHP:

<?php array(2, "William O'Neil", false);

Usually, each element appears in a separate line in YAML, but the enumeration array can also be represented in a line using square brackets:

[ 2, "William O'Neil", false ]

The following code shows how to represent an associative array in YAML:

id:       2
name:     "William O'Neil"
isActive: false

First declare the key of the element, followed by a colon and one or more spaces, and then declare the value. It's enough to have only one space after the colon, but for greater readability you can use more spaces. The equivalent PHP array of the above YAML is:

<?php array("id" => 2, "name" => "William O'Neil", "isActive" => false);

Similar to enumerated arrays, you can use braces to represent associative arrays in a row:

{ id: 2, name: "William O'Neil”, isActive: false }

Use one or more spaces for indentation, you can represent a multidimensional array like this:

- 2
- "William O'Neil"
- false

Note that although the second layer array is an enumerated array, I used the syntax of map (colon) instead of sequence (hyphen) for clarity. The above YAML block is equivalent to the following PHP:

<?php array(2, "William O'Neil", false);

YAML also allows representing a collection of multiple data elements in the same document without the need for a root node. The following example is the content of article.yml, which shows several multidimensional arrays in the same file.

[ 2, "William O'Neil", false ]

Although most of the syntax of YAML is intuitive and easy to remember, there is an important rule that needs attention. Indentation must use one or more spaces; tab characters are not allowed. You can configure the IDE to insert spaces instead of tabs when the tab key is pressed, a common configuration for software developers to ensure that the code is indented and displayed correctly when viewed in other editors. You can learn more complex features and syntax supported by YAML by reading official documentation, Symfony references, or Wikipedia.

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YAML is not a substitute for XML

If you search for YAML using search engines, you will undoubtedly find discussions about "YAML vs. XML" and naturally, when you first experience YAML, you will tend to like it more because it's easier Read and write. However, YAML should be another tool in your developer toolbox and is not necessarily a replacement for XML. Here are some of the advantages of YAML and XML.

Advantages of YAML:

• Simpler, easier to write and read
• No need for a tree structure with a single parent node

Advantages of XML:

• More built-in PHP support than YAML
• XML has always been the de facto standard for communication between applications and has been widely recognized
• XML tags can have attributes that provide more information about the data contained

Although XML is verbose, XML is easier to read and maintain when the element hierarchy is deep than YAML's space-oriented hierarchical representation. Given the advantages of both languages, YAML seems to be more suitable for collections of different data sets, and when humans are also data users.

Select PHP YAML parser

The YAML parser should have two functions: some kind of loading function that converts YAML to an array; and a dump function that converts the array to YAML. Currently, PHP's YAML parser can be used as a PECL extension and is not bundled with PHP. Alternatively, there are parsers written in pure PHP that are slightly slower than PECL extensions. Here are some YAML parsers that can be used for PHP:

• PECL extension - not bundled with PHP

• The server's root permission is required to be installed

• Symfony 1.4 YAML Component - Implemented with PHP

• Can be used in PHP version 5.2.4

• Need to be extracted from the Symfony framework

• Symfony 2 YAML component - Implemented with PHP

• Can be used in PHP version 5.3.2

• SPYC - Implemented with PHP

• Can be used in PHP 5 version

I prefer the Symfony 1.4 YAML component because it is portable (it works with PHP 5.2.4 version) and maturity (Symfony 1.4 is a complete PHP framework). After extracting the YAML component from the Symfony archive, the YAML class is located under lib/yaml. The static methods load() and dump() can be used in the sfYaml class.

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Integrate PHP YAML parser into your project

Whenever you integrate a third-party class or library into a PHP project, it is best to create a wrapper and a test suite. This allows you to change the third-party library later with minimal changes to project code (the project code should only reference the wrapper), and ensures that the changes do not break any functionality (the test suite will tell you). Below is a test case (YamlParserTest.php) created for my wrapper class (YamlParser.php). You need to understand PHPUnit to run and maintain test cases. If you prefer, you can add more tests, such as wrong file names and file extensions other than .yml, as well as other tests based on scenarios you encounter in your project.

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Summary

Now you have learned what YAML is, how to represent PHP arrays in YAML, and how to integrate PHP YAML parser in your project. By spending more time learning YAML syntax, you will be able to master the power it provides. You can also consider exploring Symfony 1.4 and 2 frameworks that use YAML extensively.

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