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PHP Trait: Populate

A simple Trait for PHP classes enabling properties to be populated and exported using the object's getters and setters but through a single method.

PopulateTrait is great because it:

• Is simple and fast - no use of code generation and such
• Uses getters and setters - always respects your public API
• Does not add overloaded methods - avoids magic behavior
• Is bi-directional - populates and exports properties
• Can perform mapping - input's property names can be different from target's
• Can populate and export properties selectively with or without mapping

Usage

Implemented as follows:

The PopulateInterface is optional - it is included to enable you to use type hinting in methods, and to be able to pass other instances as source data when populating. If you plan to pass your objects as data source to other objects, you must either implement the interface or manually call $source->exportGettableProperties(); to extract the values before you pass them to populate(). The following examples all illustrate usages where $source implements the interface.

Implemented in the class, the Trait allows the following to populate data:

And the following to export data to a simple array:

Note that in both examples when no mapping of properties' names is desired, the array acts as a list of names and not a map as such. Both methods will intelligently detect if you used a numerically indexed array or a string indexed array and behave accordingly; given that no PHP version allows class properties whose names are an integer value. When encountering a numerically indexed array, a new property name "map" (in quotes) is created using array_combine with the input as both keys and values.

Because of this the two arrays array('before' => 'before') and array('before') have the same meaning when populating or exporting.

Populating with objects: reference or clone?

When you populate an object and the input data contains other object instances, your expectation may be that clone is used on each object in order to populate with a clone, not a reference.

However, the default behavior of Populate is to populate any object values with references. If you wish to have objects cloned instead, switch to the alternative method:

This causes all object-type values to be cloned before being set on $copy.

If your requirement is that some properties be populated with clones and others with references, there are two ways to reach your goal:

Naturally, you would select the method that requires the least number of property names to be passed in the second populate operation.

The other, more obvious way is outside the scope of Populate because it manually post-processes the values to use clones/references, but it works just the same:

You can use whichever method fits your application design best. Populate provides methods which are suitable for generic usage but does not prevent you from using the existing setters and getters in any way.

Common pitfall

When populating objects with other objects as source and these other objects contain nested objects, the cloning that is performed by Populate does not happen recursively. To gain control over the cloning behavior for each object you are advised to define __clone methods on each object you need to control.

See the official PHP documentation, cloning chapter

Supported input types

The populate() method supports the following input types:

• Other PopulateTrait-implementing object instances of any type
• String-indexed arrays with property=>value syntax
• Any Iterator+ArrayAccess combination is fully supported
• ArrayAccess without Iterator is partially supported

Note that the final type, an object implementing ArrayAccess but not implementing Iterator, is only supported when using a manual list of property names along with the "only selected properties" flag.

Supported getters and setters

PopulateTrait does not care about the value types you are setting, but it does care about how your getters and setters are constructed.

In order to properly use your getters and setters, PopulateTrait requires the following to be fulfilled:

1. Getters must have no mandatory arguments
2. Setters must have no more than one mandatory argument
3. Valid getter names are (if property is name):
   1. getName
   2. isName
   3. getIsName
   4. name
4. Valid setter names are (if property is name):
   1. setName
   2. setIsName

The additional is-style method names are only attemted if the standard methods do not exist - this is done in order to accommodate the standard PHP pattern of naming boolean getters/setters using is. The getter can also be just the property name. This could be useful if the property is named like $isFinished.

Special requirements

There must be only one getter for each property. If multiple getters are found for a property, based on the rules above, an exception is thrown. This is required to ensure that the getter for a property always acts the same way.

Handling an error from PopulateTrait

Errors from PopulateTrait methods are thrown as Dkd\Populate\Exception with a unique exception code for error types, which are:

• 1422045180 when an invalid input type given to populate()

And using a more specific Dkd\Populate\AccessException for:

• 1422021211 when attempting to populate a setter-less property
• 1422021212 when attempting to export a getter-less property
• 1424776261 when multiple property accessor methods are found

The Exception type is caught as usual:

Edge cases

Being very compact and not using Reflection or any configuration of any kind, there are some edge cases that Populate cannot handle.

The edge cases and their workarounds:

• Populate does not set public properties on classes implementing the Trait. To work around this, handle your public properties manually. If your properties are already public then you do not need the logic provided by PopulateTrait in the first place.
• Populate does not support overloaded methods for getters and setters. The only "workaround" is to implement proper getters and setters.
• Populate is not recursive; populate() does not get called on child property values. To work around this, convert any values before passing them to populate(). You can create recursive methods that consume PopulateInterface instances and manually use export() and recurse those values before calling populate(). This also means that any nested object instances will not be cloned automatically when you call populateWithClones. To work around this when using arrays as source, your custom recursive methods should take care of the cloning. When using objects as source, you can implement the __clone method to control the cloning beahavior for each object.
• Populate can only use proper PHP type hints to determine an expected input type. This means that your @param annotations are not taken into consideration. Setters which perform additional validation of input arguments may still throw errors. In other words, Populate() does not attempt to catch errors from any method it calls. To work around this, manually remove any invalid values from the input data before you pass it to populate().