In a social network environment, what would be the easiest way to check for friendships globally?

For reference, here is a question on SO that I asked recently that is relevant to this question: How to model Friendship relationships

On that question, we figured out a way to display news feed items only if posted by friends. However, what I need is advice on how to check for friendship in a more dynamic way so it can be used throughout several site functions.

For example, I've just installed a comment system, allowing users to post comments on news posts. However, this isn't restricted to friends, and it should be (and later should be made optional by the author of the post).

Posting news items only by friends was slightly different because I was getting data directly from the database, and using SELECT subqueries to only get posts by friends of the current user. However, in the example of the commenting, I only want to display the comment post form if the person is a friend. I'm not actually pulling anything from the database to pick, sort, and display.

Knowing issues like this will arise many times throughout the site, what would be the simplest way to check for friendship? Could I somehow pull all the friends' user IDs from the database into a session array of some kind and then do an if(in_array($friends)) whenever I needed to determine if the person in question is a friend of the currently logged in user? Off the top of my head, this sounds like it would work fine, but I'd like your input first.

The question I linked to above 开发者_运维知识库explains how my friendship table works, in case that help you help me with this.

Actually, it is a very bad idea to stor the friend array in the session. What happens if some you add a new friend after the session variable is created? It does not get updated in the session.

Since you will be checking the list of friends a lot of times on the same page, why not just query it out and store it in a local array that you can keep using on the same page.

When the page finish executing, the array will be discarded.

So basically, you will only query the list out once.

A recommended implementation would be to follow the advise of "pst" in the above comment, and just query for every time you need to find the relationship first, as that is simple to implement. Later, when the speed of the query starts to become a issue, you can just change the internal of that method to cache the friend list in a local array when it is first called to speed things up. (exchange memory usage for processor usage).