PHP Object Relations

After some discussion in the POG Google group, it seems that we haven’t done a good enough job yet, explaining how to use POG’s optional ability to generate object-relations code. So, here it goes:

In addition to the basic 5 CRUD methods (Get, Save, GetList, SaveNew and Delete), POG is able to generate additional methods for “connected objects”. These additional methods are only generated if, upon generation, you have chosen 1 or more attributes to be of type “Child” or “Parent” from the drop-down list in the POG interface.

More often than not, objects are related to each-other in an application, so it makes sense for developers to take advantage of these generated methods. However, a developer can still decide to implement object relations without going through POG’s child/parent concept. In this case, the developer would then generate objects containing attributes that can be used as foreign keys to match them with other objects.

Explanation of POG’s parent/child concept.
POG’s parent/child concept is quite simple and is essentially an implementation of 1-to-many and many-to-1relations. A parent object can have many children (1-to-many). Many children can refer to the same parent (many-to-1). Using POG to generate Many-to-many relations is a little less obvious and currently not supported out-of-the-box, but we’re working to correct this in the next release.

Programmatic meaning:
It might be worth mentioning what a Parent or Child attribute mean on a programmatic level in POG.

RULE A
When object “P” contains a Child attribute “C”, it means that P will have:
1. a method GetCList() will be generated. GetCList returns a list of all children for parent P.
2. a method AddC() will be generated. AddC() will add any child C to the list of children belonging to P.
3. the ability to save all children, grand-children, grand-grand children etc. recursively through Save($deep).
4. the ability to delete all children, grand-children, grand-grand children etc. recursively through Delete($deep).

RULE B
When an object “C” contains a Parent attribute “P”, it means that C will have:
1. an attribute pId which refers to the Id of the Parent object.
2. A GetP() method which fetches the parent object.
3. A SetP() method which sets the parent object.

How to use POG’s interface to generate object relations. (Examples)
The rule of thumb is: Whenever an object P has a attribute C of type {Child}, the child object C must also have an attribute P of type {Parent}.

Example #1.

• An author has a name and 1 or more books
• A book has a title and only 1 author
• A publishing Company has a name and 1 or more authors

Solution:
Create an “Author” object with the following attributes:

• Book ({Child})
• Publisher ({Parent})
• name (VARCHAR)

Create a “Book” object with the following attributes:

• Author ({Parent})
• title (VARCHAR)

Create a “Publisher” object with the following attributes:

• Author ({Child})
• name (VARCHAR)

Example #2

• A project has a name, a due date and 1 or more developers
• A task has a title and belongs to 1 developer
• A developer has a name, a title and one or more tasks.

Solution:
Create a “Project” object with the following attributes:

• name (VARCHAR)
• dueDate (VARCHAR)
• Developer ({Child})

Create a “Task” object with the following attributes:

• title (VARCHAR)
• Developer ({Parent})

Create a “Developer” object with the following attributes:

• name (VARCHAR)
• title (VARCHAR)
• Task ({Child})
• Project ({Parent})

Over the next little while, we’ll be adding some more info about Relations to the POG documentation as well as to the blog, and we hope some of you find it useful.