codebright

Eloquent Relationships 351
1 +---------+------------------------+
2 | id (PK) | name |
3 +---------+------------------------+
4 | 1 | Code Sexy |
5 | 2 | Code Dutch |
6 | 3 | Code Bright |
7 | 4 | Code Happy |
8 +----------------------------------+
book_user
1 +-------------------------+
2 | id | user_id | book_id |
3 +-----+---------+---------+
4 | 1 | 1 | 2 |
5 | 2 | 1 | 3 |
6 | 3 | 2 | 2 |
7 | 4 | 3 | 2 |
8 +-----+---------+---------+
Wait a minute, what’s that third table?
Well spotted! That would be our join table, or pivot table, or lookup table, or intermediatory table,
or doing the hibbity-bibbity table. It has a lot of names. The Laravel documentation tends to refer
to them as pivot tables, so I’m going to stick with that. Whenever you need a many_to_many
relationship you will find a need for a pivot table. It’s the database table that links the two entities
together by using two foreign keys to define the rows from the other tables.
Looking at the first two rows of the pivot table, we can see that the user ‘Dayle Rees’ has favourited
both ‘Code Dutch’ and ‘Code Bright’. We can also see that the users Matthew Machuga and Shawn
McCool have both favourited Code Dutch.
There is an additional type of relationship known as a polymorphic relationship. Due to it’s complex
nature, and it’s long name, we will cover it within a later chapter on advanced Eloquent tactics. We
won’t need it yet.
That’s enough learning. It’s time for different learning! Practical learning. Now that we have
discovered the variety of relationships available, let’s learn how to implement them with Eloquent.
Implementing Relationships
Right, let’s set the stage. First we are going to need to construct some tables. Normally I’d create a
new migration for each table, but to simplify the examples I will put them all in one.