Class: Philtre::Grinder

Inherits:
Sequel::ASTTransformer
  • Object
show all
Defined in:
lib/philtre/grinder.rb

Overview

Using the expressions in the filter, transform a dataset with placeholders into a real dataset with expressions, for example:

ds = Personage.filter( :brief.lieu, :title.lieu ).order( :age.lieu )
g = Grinder.new( Philtre.new(title: 'Grand High Poobah', :order => :age.desc  ) )
nds = g.transform( ds )
nds.sql

=> SELECT * FROM "personages" WHERE (("title" = 'Grand High Poobah'))

In a sense, this is a means to defining SQL functions with optional keyword arguments.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(filter = Philtre::Filter.new) ⇒ Grinder

filter must respond to expr_for( key, sql_field = nil ), expr_hash and order_hash



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# File 'lib/philtre/grinder.rb', line 25

def initialize( filter = Philtre::Filter.new )
  @filter = filter
end

Instance Attribute Details

#filter ⇒ Object (readonly)

Returns the value of attribute filter.



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# File 'lib/philtre/grinder.rb', line 29

def filter
  @filter
end

Instance Method Details

#places ⇒ Object

Grouped hash of place holders in the original dataset from the last transform. Only has values after transform has been called.



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# File 'lib/philtre/grinder.rb', line 67

def places
  @places || raise("Call transform to find place holders.")
end

#transform(dataset, apply_unknown: true) ⇒ Object Also known as: []

pass in a dataset containing PlaceHolder expressions. you’ll get back a modified dataset with the filter values filled in.



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# File 'lib/philtre/grinder.rb', line 34

def transform( dataset, apply_unknown: true )
  @unknown = []
  @places = {}
  @subsets = []

  # handy for debugging
  @original_dataset = dataset

  # the transformed dataset with placeholders that
  # exist in filter replaced. unknown might have values
  # after this.
  t_dataset = super(dataset)
  unknown_placeholders

  if unknown.any?
    if apply_unknown
      # now filter by whatever predicates are left over
      # ie those not in the incoming dataset. Leftover
      # order parameters will overwrite existing ones
      # that are not protected by an outer select.
      filter.subset( *unknown ).apply t_dataset
    else
      raise "unknown values #{unknown.inspect} for\n#{dataset.sql}"
    end
  else
    t_dataset
  end
end

#unknown ⇒ Object

collection of values in the filter that were not found as placeholders in the original dataset.



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# File 'lib/philtre/grinder.rb', line 73

def unknown
  @unknown || raise("Call transform to find placeholders not provided by the filter.")
end