The King of Relations: ManyToOne
Selecting between ManyToOne and ManyToMany
Each genus will have many genus_notes. But, each genus_note that someone adds
will relate to only one genus. There are only two possible types of relationships,
and this is by far the most common. It's called a ManyToOne association.
The second type is called a ManyToMany association. To use a different example,
this would be if each product had many tags, but also each tag related to many
products.
And when it comes to Doctrine relations - don't trust the Internet! Some people
will try to confuse you with other relationships like OneToMany, OneToOne and some
garbage about unidirectional and bidirectional associations. Gross. Ignore it all.
I guarantee, all of that will make sense really soon.
So your first job is simple: decide if you have a ManyToOne or ManyToMany relationship.
And it's easy. Just answer this question:
Do either of the sides of the relationship belong to only one of the other?
Each genus_note belongs to only one genus, so we have a classic ManyToOne relationship.
Setting up a ManyToOne Relation
Forget about Doctrine: just think about the database. If every genus_note should
belong to exactly one genus, How would you set that up? You'd probably add a
genus_id column to the genus_note table. Simple!
Since we need to add a new column to GenusNote, open that entity class. You probably
feel like you want to add a $genusId integer property here. That makes sense. But
don't! Instead, add a $genus property and give it a ManyToOne annotation. Inside
that, add targetEntity="Genus":
| // ... lines 1 - 10 | |
| class GenusNote | |
| { | |
| // ... lines 13 - 39 | |
| /** | |
| * @ORM\ManyToOne(targetEntity="Genus") | |
| */ | |
| private $genus; | |
| // ... lines 44 - 98 | |
| } |
Tip
You can also use the full namespace: AppBundle\Entity\Genus - and that's required
if the two entities do not live in the same namespace/directory.
Umm, guys? That's it. Relationship finished. Seriously.
