In this post we will review how to define Doctrine relationships, from one-to-one to many-to-many relationships.
One-to-One
To explain this relationship we do it with an example. We suppose that we have two entities (User and Email); when we define the Email entity we should add a ‘user_id‘ property (which is the foreign key) due to the User entity is the “owner” of the relationship, this means the User has an Email. We always need to identify the “owner” side and add the foreign key to the entity which belongs to the “owner” entity. When we use this relationship, Doctrine uses a hasOne method. Let’s see how to define it with yaml:
1 2 3 4 5 6 7 8 9 | Email: columns: user_id: integer address: string(150) relations: User: local: user_id foreign: id foreignType: one |
One-to-Many and Many-to-One
Now, let’s suppose we have the same User entity which can have many phone numbers (for that we have a Phonenumber entity). We should follow the same convention than in the one-to-one relationship and define the foreign key in the Phonenumber entity, which belongs to the User entity. When we define this kind of relationship Doctrine uses the hasOne method for the Phonenumber entity and the hasMany method for the User entity. Let’s see how to define it with yaml:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | User: // Some properties definitions here relations: Phonenumbers: type: many class: Phonenumber local: id foreign: user_id Phonenumber: columns: user_id: integer phonenumber: string(50) relations: User: local: user_id foreign: id |
Many-to-Many
And last but not least, when we need to define a many-to-many we have the need to add an extra table :-S, called JOIN table. Following with our User entity, let’s suppose we have a new entity called Group, and we know that a User can belong to a many Groups and that a Group can have a lot of Users. In this case, if we remove an User we should not remove the Group, but yes the relationship. When we define this kind of relationship Doctrine uses the hasMany method in both entities. Let’s see how to define it with yaml:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | User: // Some properties definition here relations: Groups: class: Group local: user_id foreign: group_id refClass: UserGroup Group: tableName: groups columns: name: string(30) relations: Users: class: User local: group_id foreign: user_id refClass: UserGroup UserGroup: columns: user_id: type: integer primary: true group_id: type: integer primary: true |
Well, I hope this post will be helpful to understand and know how to define Doctrine relationships.
