JoinOperators

Join Operations¶ ↑

• Cross Join

  categories = [ "Beverages", "Condiments", "Vegetables", "Dairy Listings", "Seafood" ]
  products = [Listing.new("keyboard","computers"),Listing.new("pepsi","Beverages"),Listing.new("peppers","Vegetables"),Listing.new("coke","Beverages"),Listing.new("ice cream","Dairy Listings")]
  results = _{
    from c in_ categories
    join p in_ products on c equals p.category
    select  category:  c, name:  p.name
  }
  results.to_a.count.should == 4
  results.to_a.collect(&:name).should == ["pepsi", "coke", "peppers",

• multi join

  categories = [ "Beverages", "Condiments", "Vegetables", "Dairy Listings", "Seafood" ]
  products = [Listing.new("keyboard","computers"),Listing.new("pepsi","Beverages"),Listing.new("peppers","Vegetables"),Listing.new("coke","Beverages"),Listing.new("ice cream","Dairy Listings")]
  tag_lines = [TagLine.new("People Work on these","computers"),TagLine.new("People Drink these","Beverages"),TagLine.new("People Eat These","Vegetables")]
  results = _{
    from c in_ categories
    join p in_ products on c equals p.category
    join t in_ tag_lines on c equals t.category
    select  category:  c, name:  p.name, tag_line: t.tag_line
  }
  results.to_a.count.should == 3
  results.to_a.collect(&:name).should == ["pepsi",

• group join

  categories = [ "Beverages", "Condiments", "Vegetables", "Dairy Listings", "Seafood" ]
  products = [Listing.new("keyboard","computers"),Listing.new("pepsi","Beverages"),Listing.new("peppers","Vegetables"),Listing.new("coke","Beverages"),Listing.new("ice cream","Dairy Listings")]
  results = _{
    from c in_ categories
    join p in_ products on c equals p.category into ps
    select  category:  c, products:  ps
  }
  results.to_a.count.should == 3
  results.to_a.collect(&:category).should == ["Beverages", "Vegetables", "Dairy Listings"]
  results.to_a.collect(&:products).first.collect(&:name).should == ["pepsi", "coke"]
  results.to_a.collect(&:products)[1].collect(&:name).should == ["peppers"]
  results.to_a.collect(&:products)[2].collect(&:

• Cross Join with Group Join

  categories = [ "Beverages", "Condiments", "Vegetables", "Dairy Listings", "Seafood" ]
  products = [Listing.new("keyboard","computers"),Listing.new("pepsi","Beverages"),Listing.new("peppers","Vegetables"),Listing.new("coke","Beverages"),Listing.new("ice cream","Dairy Listings")]
  results = _{
    from c in_ categories
    join p in_ products on c equals p.category into ps
    from p in_ ps
    select  category:  c, product:  p.name
  }
  results.collect{|a|[a.category,a.product]}.should == [["Beverages","pepsi"], ["Beverages","coke"], ["Vegetables","peppers"], ["Dairy Listi