when/where does Rails convert "params" used to populate a model object from a form, into their correct types in the model object??? (i.e. from "string")

Greg_H · November 26, 2008, 9:43pm

Hi,

When/where does Rails convert "params" used to populate a model object from a form, into their correct types in the model object??? (i.e. from "string") What part of rails does this?

I have a form upload and in my create method where I go :@graph_options = GraphOptions.new(params[:graph_options])" it is not doing the type conversion, as the attributes remain as strings.

Note I am using BaseWithoutTable

Frederick_Cheung · November 27, 2008, 7:31am

Hi,

When/where does Rails convert "params" used to populate a model object from a form, into their correct types in the model object??? (i.e. from "string") What part of rails does this?

Well it's the call to column.typecast here:

github.com

rails/rails/blob/2-2-stable/activerecord/lib/active_record/attribute_methods.rb

module ActiveRecord
  module AttributeMethods #:nodoc:
    DEFAULT_SUFFIXES = %w(= ? _before_type_cast)
    ATTRIBUTE_TYPES_CACHED_BY_DEFAULT = [:datetime, :timestamp, :time, :date]

    def self.included(base)
      base.extend ClassMethods
      base.attribute_method_suffix(*DEFAULT_SUFFIXES)
      base.cattr_accessor :attribute_types_cached_by_default, :instance_writer => false
      base.attribute_types_cached_by_default = ATTRIBUTE_TYPES_CACHED_BY_DEFAULT
      base.cattr_accessor :time_zone_aware_attributes, :instance_writer => false
      base.time_zone_aware_attributes = false
      base.class_inheritable_accessor :skip_time_zone_conversion_for_attributes, :instance_writer => false
      base.skip_time_zone_conversion_for_attributes = []
    end

    # Declare and check for suffixed attribute methods.
    module ClassMethods
      # Declares a method available for all attributes with the given suffix.
      # Uses +method_missing+ and <tt>respond_to?</tt> to rewrite the method

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Which is defined here:

github.com

rails/rails/blob/2-2-stable/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb

require 'date'
require 'set'
require 'bigdecimal'
require 'bigdecimal/util'

module ActiveRecord
  module ConnectionAdapters #:nodoc:
    # An abstract definition of a column in a table.
    class Column
      TRUE_VALUES = [true, 1, '1', 't', 'T', 'true', 'TRUE'].to_set

      module Format
        ISO_DATE = /\A(\d{4})-(\d\d)-(\d\d)\z/
        ISO_DATETIME = /\A(\d{4})-(\d\d)-(\d\d) (\d\d):(\d\d):(\d\d)(\.\d+)?\z/
      end

      attr_reader :name, :default, :type, :limit, :null, :sql_type, :precision, :scale
      attr_accessor :primary

      # Instantiates a new column in the table.

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(but possibly overriden by individual connection adapters).

How that interacts with BaseWithoutTable I have no idea.

Fred

Greg_H · November 27, 2008, 7:54am

thanks - I'll have a look at the code - so would it be correct to say then that the Rails framework does effectively cast the params strings to their type prior to any saves to the data? (i.e. its not like it leave this up to the database to do itself is it, i.e. like if there was a date it doesn't just pass the string representation of the data through to the database to store in it's Date field)

Frederick_Cheung · November 27, 2008, 10:15am

thanks - I'll have a look at the code - so would it be correct to say then that the Rails framework does effectively cast the params strings to their type prior to any saves to the data? (i.e. its not like it leave this up to the database to do itself is it, i.e. like if there was a date it doesn't just pass the string representation of the data through to the database to store in it's Date field)

Actually it doesn't (minor exception in that a blank string is turned into nil for numbers). typecasting happens in read_attribute (check the source for read/write_attribute.

Fred

Greg_H · November 27, 2008, 10:43am

ohhh, thanks. Things make sense now when I look at my object state in debug & see the strings..

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when/where does Rails convert "params" used to populate a model object from a form, into their correct types in the model object??? (i.e. from "string")

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