Oomoo

March 5, 2008

A Model Is A Class

Filed under: classes, model — oomoo @ 11:09 pm

A Model Is A Class

A “Model” is a Class that deals with the manipulation of data.  Classes allow the combination of data and methods in one place.  Because it is a full-blown Class, it can have any number of its own variables and methods.

The Model class is the perfect place for data validation for a Rails system. It actually makes more sense to store data-based logic here than in the database (assuming that other systems are not monkeying with your data). This is one of the reasons most Rails programmers don’t use database constraints (one of the big reasons is ActiveRecord doesn’t like it either).


Generally, a Model Class is comprised of several things:

  • Associations (Relationships to other tables in the database)
  • Validations (special rails “validates…” statements)
  • Accessors (creates “getter” and “setter” methods automatically) (methods used to get/put data in a private class variable)
  • CallBacks (hooks into the underlying rails logic that allow you to inject your code a specific steps)
  • Class Variables (@@varname, only one set maintained across all objects of the class)
  • Instance Variables (@varname, each object has its own set to manipulate at will)
  • Class Methods (generic logic methods not tied to specific data) (or operate on the class itself, like instance counters)
  • Instance Methods (any method that is not a class method)


# Associations
=======================================================

has_one :order_account_type
has_many :orders
belongs_to :order_address
belongs_to :order_user
belongs_to :order
 

# Validations
=======================================================

validates_presence_of :order_user_id, :order_address_id, :order_id
validates_length_of :cc_number, :maximum => 20
validates_format_of :cc_number, :with =>
/^[\d]*$/, :message => ERROR_NUMBER
validates_format_of :credit_ccv, :with => /^[\d]*$/, :message => ERROR_NUMBER
validates_numericality_of :expiration_month, :expiration_year

# Accessors
=======================================================
attr_accessor :name, :promotion_code, cc_number

# CALLBACKS
==========================================================

before_save :set_product_cost
before_destroy{|record | Person.destroy_all “firm_id=#{record.id}”}

During the life cycle of an active record object, you can hook into 8 events:
  (-) save
  (-) valid?
  (1) before_validation
  (2) before_validation_on_create
  (-) validate
  (-) validate_on_create
  (3) after_validation
  (4) after_validation_on_create
  (5) before_save
  (6) before_create
  (-) create
  (7) after_create
  (8) after_save


# CLASS VARIABLES
=======================================================

@@number_of_instances
@@version
# INSTANCE VARIABLES
=======================================================
@total_line_items
@time_created
# CLASS METHODS
=======================================================
# List of years for dropdown in UI

def self.years
  start_year = Date.today.year
  years = Array.new
  10.times do
    years << start_year
    start_year +=
1
  end
  return
years
end # Search by order_number
def self.search(search_term, count=false, limit_sql=nil)
  if (count == true) then
    sql = “SELECT COUNT(*) ”
  else
    sql = “SELECT DISTINCT orders.* ”
  end
  sql << “FROM orders ”
  sql << “WHERE orders.order_number = ? ”
  sql << “ORDER BY orders.created_on DESC ”
  sql << “LIMIT #{limit_sql}” if limit_sql arg_arr = [sql, search_term, “%#{search_term}%”]

  if
(count == true) then
    count_by_sql(arg_arr)
  else
    find_by_sql(arg_arr)
  end
end

# INSTANCE METHODS
==========================================================

def
status
  code = OrderStatusCode.find(
:first, :conditions => [“id = ?”, self.order_status_code_id])
  code.name
end def tax_cost
  (
self.line_items_total) * (self.tax/100)
end

def
name
  return “#{billing_address.first_name} # billing_address.last_name}”
end

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