Thursday, 12 April 2012

Entities vs Nodes

For the last six months I've been working on a Drupal 6 site professionally, but developing a couple of personal Drupal 7 sites. However I haven't been going into D7 in any great detail - except for developing entities.

Now I've moved contracts and I'm developing a new Drupal 7 site to replace an older non-Drupal site with lots of additional facilities. And the Drupal implementation is entirely up to me.

Being an OOP person at heart I love the concept of entities but when working with a commercial website you have to make some serious decisions. My personal preferences have to give way to the reality of building a website that delivers the spec and can be maintained and extended by other developers in the future.

So how do you decide what should be a node and what should be an entity?

There's a line in this blog post which says:
You can now actually create data structures specific to your application domain with their own database table (or any other storage mechanism really) plus a standardised way to add fields to them. No need to turn nodes into something they are not.
Which is technically accurate but does not always provide clear guidance, so here's my step-by-step analysis method to decide whether a specific data structure should be a node or not:

1. Is it content? Is the item definitely stuff that gets turned into HTML and displayed for the user? If you were building a review site, a review would definitely be content, so that's a node.

2. Does it need to have revisions? The node module provides revisions and the associated modules make it easy and powerful. Building revisions into custom entities is hard. So if it has to have revisions then it has to be a node.

3. Is there additional "property" (as opposed to "field") information? I had a situation where I wanted to define a "proxy", and a proxy needs a web address, a port number, maybe a username and password. These are fundamental properties of a proxy. You could add these as fields for a node, of course, but it makes more sense for them to be properties of a proxy entity. So this should be considered as an entity. (Another way of looking at this is: is there a need for a new table containing information specific to this data structure? If so, think entity.)

4. Is the structure normally invisible to the user? That should be an entity.

5. Would using an entity instead of a node obscure the function? Perhaps this is tricky to answer, after all dividing functionality out to a new object should never make things more complex. But it's worth asking the question.

Any other ways of to help make the decision?

Remember: there is virtually no overhead in creating a new entity. And there are huge advantages in additional functionality that the core, Entity API, Views, Features and other entity-related modules can give you.