Rails Relationship basics
How to make relationships for rails?
Association
Model Database relationships
No Relationship
@item = Item.find(1) @category = Category.where(:item_id => @item.id)
Relationship
@item = Item.find(1) @category = @item.categories
Relationships and Name rule
Relationships are 1:1, 1:n, m:n
To express relationships, we have to follow name rules
- Foregn key column name is “reftablemodel_id” example (item_id, user_id)
- If you use middlein table, you use table1_table2 example (authors_books)
Database?
This is not actually foreign key in database.
List
| Name | Description |
|---|---|
| belongs_to | Access from ref table |
| has_many | Reverse of belong_to, Create 1:n to 1 object |
| has_one | 1:1, or 1:0..1 |
| has_and_belongs_to_many | n:m |
| has_many:through | m:n, and cross over model(middlein table) |
Let’s see each cases.