require 'spec_helper'
module Alf
  describe Relation do
    
    let(:rel1){Alf::Relation[
      {:sid => 'S1'},
      {:sid => 'S2'},
      {:sid => 'S3'}
    ]}
    
    let(:rel2){Alf::Relation[
      {:sid => 'S5'},
      {:sid => 'S2'}
    ]}

    specify "project" do
      rel1.project([]).should eq(Alf::Relation[{}])
      rel1.project([:sid], :allbut => true).should eq(Alf::Relation[{}])
    end
    
    specify "allbut" do
      rel1.allbut([:sid]).should eq(Alf::Relation[{}])
    end
    
    specify "extend" do
      rel1.extend(:x => lambda{ sid.downcase }).should == Alf::Relation[
        {:sid => 'S1', :x => 's1'},
        {:sid => 'S2', :x => 's2'},
        {:sid => 'S3', :x => 's3'}
      ]
    end
      
    specify "union" do
      (rel1 + rel1).should == rel1
      (rel1 + rel2).should == Alf::Relation[
        {:sid => 'S1'},
        {:sid => 'S3'},
        {:sid => 'S2'},
        {:sid => 'S5'}
      ]
    end # coerce
      
    specify "difference" do
      (rel1 - rel1).should == Alf::Relation[]
      (rel1 - rel2).should == Alf::Relation[
        {:sid => 'S1'},
        {:sid => 'S3'}
      ]
      (rel2 - rel1).should == Alf::Relation[
        {:sid => 'S5'}
      ]
    end # coerce
    
  end
end