Rails Development Details (vii) ACTIVERECORD Associations Association

1. Why do I need to associate

Many times, such as E-commerce users and orders, a user will have a lot of orders, an order belongs to only one user, this is an association.

When creating an order, you need to use the householder key as a foreign key to delete the user's order while deleting the user's.

In rails, you can associate an order like this to the following.

Class Customer < ActiveRecord::Base 
  has_many:orders,:d ependent =>:d estroy 
End 
      
Class Order < ActiveRecord::Base 
  belongs_to:customer 
End

You can create orders like the following, deleting users.

@order = @customer. Orders.create (: order_date => time.now) 
     
@customer. Destroy

2. Type of association

is associated with the following 6.

Belongs_to

Has_one

Has_many

Has_many:through

Has_one:through

Has_and_belongs_to_many

2.1.belongs_to

BELONGS_TO is a one-to-one association. Express a kind of relationship that belongs to.

Just like an order can only belong to a user. There is a field in the order table that stores the user's primary key, which is the foreign key of the order table.

Class Order < ActiveRecord::Base 
  Belongs_to:customer 
End

2.2.has_one

Has_one is also a one-to-one association. Expressing a relationship that has one.

Just like a supplier can only have one account. The Account table has a supplier primary key, which is the foreign key of the account table.

Class Supplier < activerecord::base 
  Has_one:account 
End

2.3.has_many

Has_many is a one-to-many association. Expresses a number of relationships.

Just like a user has multiple orders.

Class Customer < activerecord::base 
  has_many:orders 
End

The name associated with Has_many needs to be in the plural form.