Active Record Associations - 1

The 7th Round of ROR Lab.

February 18th, 2012

Hyoseong ChoiROR Lab.

ROR Lab.

For what?

ROR Lab.

For what?

To add an order

ROR Lab.

For what?

To add an order

ROR Lab.

For what?

To add an order

To delete orders

ROR Lab.

For what?

To add an order

To delete orders

ROR Lab.

For what?

• Automation of connecting btw models

• Automatic assignment of foreign key

ROR Lab.

For what?

customer order

id idid

Primary & Foreign Keys

ROR Lab.

For what?

customer order

customer_id

id id

parent obj. child obj.

Primary & Foreign Keys

ROR Lab.

For what?

customer order

customer_id

id id

parent obj. child obj.

Active Record Assocation

Primary & Foreign Keys

ROR Lab.

For what?

ROR Lab.

For what?

To add an order

ROR Lab.

For what?

To add an order

ROR Lab.

For what?

To add an order

To delete orders

ROR Lab.

For what?

To add an order

To delete orders

ROR Lab.

AssociationsParent ClassParent Class Child Class

1 : 1has_onehas_one

belongs_to1 : 1has_one, :throughhas_one, :through

belongs_to

1 : n has_manyhas_many belongs_to

n : m

Ahas_many

belongs_ton : m

Ahas_many B, :through

belongs_ton : m

Bhas_many

belongs_ton : m

Bhas_many A, :through

belongs_ton : m

has_and_belongs_to_manyhas_and_belongs_to_manyhas_and_belongs_to_many

ROR Lab.

Association Optionshas_one options• :as• :autosave• :class_name• :conditions• :dependent• :foreign_key• :include• :order• :primary_key• :readonly• :select• :source• :source_type• :through• :validate

has_many options• :as• :autosave• :class_name• :conditions• :counter_sql• :dependent• :extend• :finder_sql• :foreign_key• :group• :include• :limit• :offset• :order• :primary_key• :readonly• :select• :source• :source_type• :through• :uniq• :validate

HABTM options• :association_foreign_key• :autosave• :class_name• :conditions• :counter_sql• :delete_sql• :extend• :finder_sql• :foreign_key• :group• :include• :insert_sql• :join_table• :limit• :offset• :order• :readonly• :select• :uniq• :validate

belongs_to options• :autosave• :class_name• :conditions• :counter_cache• :dependent• :foreign_key• :include• :polymorphic• :readonly• :select• :touch• :validate

ROR Lab.

belongs_to vshas_one

• “belongs_to” model has a foreign key

• dependent upon the actual meaning of data

ROR Lab.

has_many :through vs has_and_belongs_to_many

๏ has_many

- validations, callbacks, or extra attributes

๏ has_and_belongs_to_many

- no need for additional functionalities

- should create a “join” table in the DB.

ROR Lab.

Join TableHABTM

• Default join table btw Customer & Order models : custormers_orders

• Otherwise, :join_table => “join_table_name”

ROR Lab.

Join TableHABTM

ROR Lab.

Join TableHABTM

no need for join model

ROR Lab.

Product

id

Employee

id

Polymorphic

ROR Lab.

Product

id

Employee

id

PolymorphicPicture

ROR Lab.

Product

id

Employee

id

PolymorphicPicture

employee_id

ROR Lab.

Product

id

Employee

id

Picture

PolymorphicPicture

employee_id

ROR Lab.

Product

id

Employee

id

Picture

PolymorphicPicture

employee_id

product_id

ROR Lab.

Product

id

Employee

id

Picture

PolymorphicPicture

employee_id

product_idx

ROR Lab.

PolymorphicPicture

imageable_id

Picture

imageable_id

Imageable

Imageable

id

id

ROR Lab.

PolymorphicPicture

imageable_id

Picture

imageable_id

Imageable

Imageable

Employee

Product

id

id

id

id

ROR Lab.

PolymorphicModel Class

ROR Lab.

PolymorphicMigration

ROR Lab.

Self Joins

• ex. : following or follower

ROR Lab.

Screencastfor Self Join

Please click the above link

ROR Lab.

:include

• To eager-load the second-order association

ROR Lab.

:include

• To eager-load the second-order association

@line_item.order.customer

ROR Lab.

:include

• To eager-load the second-order association

@line_item.order.customer

ROR Lab.

:counter_cache

SELECT COUNT(*) from ...

ROR Lab.

:counter_cache

@customer.orders.sizeSELECT COUNT(*) from ...

ROR Lab.

:counter_cache

@customer.orders.sizeSELECT COUNT(*) from ...

ROR Lab.

:counter_cache

@customer.orders.sizeSELECT COUNT(*) from ...

ROR Lab.

:counter_cache• But, you should add “orders_count”

column to Customer model

• You can override the default column name.

• ReadOnly !!!

ROR Lab.

:counter_cache• But, you should add “orders_count”

column to Customer model

• You can override the default column name.

• ReadOnly !!!

ROR Lab.

Screencast for Belongs_to

:counter_cache

Please click the above link

ROR Lab.

:touch

• Automatically set :updated_at or :update_on to current timestamp whenever child objects are saved or updated

ROR Lab.

:touch

ROR Lab.

:touch

ROR Lab.

:touch

Or using a custom attribute

ROR Lab.

:touch

Or using a custom attribute

ROR Lab.

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