Question

I am trying to get into some more advanced web development techniques and have a few projects in mind that require object relationships. I am developing in PHP and am planning on making the site completely object orientated.

Websites like Facebook have relationships between users, friends, groups, events, likes, posts, comments, ect. A user can belong to a group or many groups and a group can have many users. This same kind of relationship is true for events, likes, posts, comments, ect. So my question is how are these relationships handled and saved?

Obviously there is a very complex database that holds the actual content but when defining relationships such as “Which user belongs to which groups?”, how is this handled? Would all groups have a unique identification such as a hash or id number? And then a user has a “mygroups” array or such that continues to add/delete group ids which render the user a part of a group or not.

I may be way off track but any light shed on my question would be great. Thanks!

Answer 1

Let’s take an example. Users and Group.

It is a MANY to MANY relation ship. That means one user can be in 0 ore more group and One group can have one ore more Users

So There will be 3 Tables

USER Table

USER_ID (INT) Primary Key
USER_NAME V(VARCHAR)

GROUP Table

GROUP_ID (INT) Primary Key
GROUP_NAME (INT) 

USER_GROUP

USER_GROUP_ID (INT) Primary Key
GROUP_ID (INT) Foriegn Key (to GROUP Table, GROUP_ID Column)
USER_ID (INT) Foriegn Key (to USERTable, USER_ID Column)

Some sample data will be like

USER

 USER_ID              USER_NAME
 --------------------------------
 1                    Scott
 2                    Jon
 3                    Mike

GROUP

 GROUP_ID              GROUP_NAME
 --------------------------------
 161                    Bloggers
 162                    Geeks

USER_GROUP

 USER_GROUP_ID   USER_ID              GROUP_ID
 ----------------------------------------------
   1                1                    161
   2                2                    161
   3                2                    162
   4                3                    161

This means

1) Scott, Jon & Mike are present in Bloggers group.

2) Scott is present int eh Geeks group.