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Summary Given a Hash, what is the most efficient way to create a subset Hash based on a list of keys to use? h1 = { a:1, b:2, c:3 } # Given a hash... p foo( h1, :a, :c, :d ) # ...create a method that... #=> { :a=>1, :c=>3, :d=>nil } # ...returns specified keys... #=> { :a=>1, :c=>3 } # ...or perhaps only keys that exist Details The Sequel database toolkit allows one to create or update a model instance by passing in a Hash: foo = Product.create( hash_of_column_values ) foo.update( another_hash ) The Sinatra web framework makes available a Hash named params that includes form variables, querystring parameters and also route matches. If I create a form holding only fields named the same as the database columns and post it to this route, everything works very conveniently: post "/create_product" do new_product = Product.create params redirect "/product/#{new_product.id}" end However, this is both fragile and dangerous. It's dangerous because a malicious hacker could post a form with columns not intended to be changed and have them updated. It's fragile because using the same form with this route will not work: post "/update_product/:foo" do |prod_id| if product = Product[prod_id] product.update(params) #=> <Sequel::Error: method foo= doesn't exist or access is restricted to it> end end So, for robustness and security I want to be able to write this: post "/update_product/:foo" do |prod_id| if product = Product[prod_id] # Only update two specific fields product.update(params.slice(:name,:description)) # The above assumes a Hash (or Sinatra params) monkeypatch # I will

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