module ActiveRecord::Sanitization::ClassMethods

def expand_hash_conditions_for_aggregates(attrs)

# => { address_street: "813 abc st.", address_city: "chicago" }
{ address: Address.new("813 abc st.", "chicago") }
Then:
end
mapping: [%w(address_street street), %w(address_city city)]
composed_of :address, class_name: "Address",
class Person < ActiveRecord::Base
Given:
aggregate attribute values.
that correspond to a +composed_of+ relationship with their expanded
Accepts a hash of SQL conditions and replaces those attributes 
def expand_hash_conditions_for_aggregates(attrs)
  expanded_attrs = {}
  attrs.each do |attr, value|
    if aggregation = reflect_on_aggregation(attr.to_sym)
      mapping = aggregation.mapping
      mapping.each do |field_attr, aggregate_attr|
        if mapping.size == 1 && !value.respond_to?(aggregate_attr)
          expanded_attrs[field_attr] = value
        else
          expanded_attrs[field_attr] = value.send(aggregate_attr)
        end
      end
    else
      expanded_attrs[attr] = value
    end
  end
  expanded_attrs
end

def quote_bound_value(value, c = connection) #:nodoc:

:nodoc: 
def quote_bound_value(value, c = connection) #:nodoc:
  if value.respond_to?(:map) && !value.acts_like?(:string)
    if value.respond_to?(:empty?) && value.empty?
      c.quote(nil)
    else
      value.map { |v| c.quote(v) }.join(',')
    end
  else
    c.quote(value)
  end
end

def quote_value(value, column = nil) #:nodoc:

:nodoc: 
def quote_value(value, column = nil) #:nodoc:
  connection.quote(value,column)
end

def raise_if_bind_arity_mismatch(statement, expected, provided) #:nodoc:

:nodoc: 
def raise_if_bind_arity_mismatch(statement, expected, provided) #:nodoc:
  unless expected == provided
    raise PreparedStatementInvalid, "wrong number of bind variables (#{provided} for #{expected}) in: #{statement}"
  end
end

def replace_bind_variable(value, c = connection) #:nodoc:

:nodoc: 
def replace_bind_variable(value, c = connection) #:nodoc:
  if ActiveRecord::Relation === value
    value.to_sql
  else
    quote_bound_value(value, c)
  end
end

def replace_bind_variables(statement, values) #:nodoc:

:nodoc: 
def replace_bind_variables(statement, values) #:nodoc:
  raise_if_bind_arity_mismatch(statement, statement.count('?'), values.size)
  bound = values.dup
  c = connection
  statement.gsub('?') do
    replace_bind_variable(bound.shift, c)
  end
end

def replace_named_bind_variables(statement, bind_vars) #:nodoc:

:nodoc: 
def replace_named_bind_variables(statement, bind_vars) #:nodoc:
  statement.gsub(/(:?):([a-zA-Z]\w*)/) do
    if $1 == ':' # skip postgresql casts
      $& # return the whole match
    elsif bind_vars.include?(match = $2.to_sym)
      replace_bind_variable(bind_vars[match])
    else
      raise PreparedStatementInvalid, "missing value for :#{match} in #{statement}"
    end
  end
end

def sanitize(object) #:nodoc:

:nodoc:
Used to sanitize objects before they're used in an SQL SELECT statement. Delegates to connection.quote. 
def sanitize(object) #:nodoc:
  connection.quote(object)
end

def sanitize_sql_array(ary)

["name='%s' and group_id='%s'", "foo'bar", 4] returns "name='foo''bar' and group_id='4'"
sanitized and interpolated into the SQL statement.
Accepts an array of conditions. The array has each value 
def sanitize_sql_array(ary)
  statement, *values = ary
  if values.first.is_a?(Hash) && statement =~ /:\w+/
    replace_named_bind_variables(statement, values.first)
  elsif statement.include?('?')
    replace_bind_variables(statement, values)
  elsif statement.blank?
    statement
  else
    statement % values.collect { |value| connection.quote_string(value.to_s) }
  end
end

def sanitize_sql_for_assignment(assignments, default_table_name = self.table_name)

{ name: nil, group_id: 4 } returns "name = NULL , group_id='4'"
them into a valid SQL fragment for a SET clause.
Accepts an array, hash, or string of SQL conditions and sanitizes 
def sanitize_sql_for_assignment(assignments, default_table_name = self.table_name)
  case assignments
  when Array; sanitize_sql_array(assignments)
  when Hash;  sanitize_sql_hash_for_assignment(assignments, default_table_name)
  else        assignments
  end
end

def sanitize_sql_for_conditions(condition, table_name = self.table_name)

"name='foo''bar' and group_id='4'" returns "name='foo''bar' and group_id='4'"
{ name: "foo'bar", group_id: 4 } returns "name='foo''bar' and group_id='4'"
["name='%s' and group_id='%s'", "foo'bar", 4] returns "name='foo''bar' and group_id='4'"
them into a valid SQL fragment for a WHERE clause.
Accepts an array, hash, or string of SQL conditions and sanitizes 
def sanitize_sql_for_conditions(condition, table_name = self.table_name)
  return nil if condition.blank?
  case condition
  when Array; sanitize_sql_array(condition)
  when Hash;  sanitize_sql_hash_for_conditions(condition, table_name)
  else        condition
  end
end

def sanitize_sql_hash_for_assignment(attrs, table)

# => "status = NULL , group_id = 1"
{ status: nil, group_id: 1 }
Sanitizes a hash of attribute/value pairs into SQL conditions for a SET clause. 
def sanitize_sql_hash_for_assignment(attrs, table)
  attrs.map do |attr, value|
    "#{connection.quote_table_name_for_assignment(table, attr)} = #{quote_bound_value(value)}"
  end.join(', ')
end

def sanitize_sql_hash_for_conditions(attrs, default_table_name = self.table_name)

# => "address_street='123 abc st.' and address_city='chicago'"
{ address: Address.new("123 abc st.", "chicago") }
And for value objects on a composed_of relationship:
# => "`other_records`.`id` = 7"
{ other_records: { id: 7 } }
# => "`other_records`.`id` = 7"
{ 'other_records.id' => 7 }
# => "age BETWEEN 13 AND 18"
{ age: 13..18 }
# => "status IS NULL and group_id IN (1,2,3)"
{ status: nil, group_id: [1,2,3] }
# => "name='foo''bar' and group_id= 4"
{ name: "foo'bar", group_id: 4 }
Sanitizes a hash of attribute/value pairs into SQL conditions for a WHERE clause. 
def sanitize_sql_hash_for_conditions(attrs, default_table_name = self.table_name)
  attrs = expand_hash_conditions_for_aggregates(attrs)
  table = Arel::Table.new(table_name, arel_engine).alias(default_table_name)
  PredicateBuilder.build_from_hash(self, attrs, table).map { |b|
    connection.visitor.accept b
  }.join(' AND ')
end