Class: SimplerDB::QueryEvaluator

Inherits:
Dhaka::Evaluator
  • Object
show all
Defined in:
lib/simplerdb/query_language.rb

Overview

The query evaluator. This class acts on the parse tree and will return a list of item names that match the query from the evaluate method.

Instance Method Summary collapse

Constructor Details

#initialize(domain = nil) ⇒ QueryEvaluator

Returns a new instance of QueryEvaluator.



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# File 'lib/simplerdb/query_language.rb', line 150

def initialize(domain = nil)
  @domain = domain
  @predicate_identifier = nil
  @all_items = nil
end

Instance Method Details

#all_items ⇒ Object 



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# File 'lib/simplerdb/query_language.rb', line 237

def all_items
  unless @all_items
    @all_items = @domain.items.collect { |k,v| k }.to_set
  end
  
  return @all_items
end

#do_comparison(identifier, op, constant, negate = false) ⇒ Object

Apply the given comparison params to every item in the domain



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# File 'lib/simplerdb/query_language.rb', line 246

def do_comparison(identifier, op, constant, negate = false)  
  results = Set.new
  
  if @domain
    @domain.items.each_value do |item|
      attrs = item.attributes[identifier]
      
      attrs.each do |attr|
        match = op.call(constant, attr.value)
        if (match && !negate) || (negate && !match)
          results << item
          break
        end
      end
    end
  end
  
  results
end

#val(node) ⇒ Object 



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# File 'lib/simplerdb/query_language.rb', line 233

def val(node)
  node.token.value.to_s[1..-2]
end