Support providing arbitrary SQL strings

This commit provides a low level extension point in the
hash structure to provide a lambda that returns the section of the query that
is being asked for.

This allows people to query for any DB types or operated that aren't directly
supported in SearchCop, and SearchCop doesn't have to support them.

It's a pretty low level API in that it expects you to know about what nodes and
visitors are, but this seems like a starting point that gets users past being
stuck, and could be built on in the future.

One of those things that I think could be useful is providing this same
structure, but as one of the `options` instead and that would be used every time
you query for that said attribute. The downside of the method proposed in this
PR is that you have to use the hash parser, and inline your SQL there and every
other place you want to use it. Providing it as a default option would allow
that.

Related to mrkamel#31 and mrkamel#28.

README.md

@@ -33,6 +33,7 @@ Book.search(:author => "Rowling", :title => "Harry Potter")
 Book.search(:or => [{:author => "Rowling"}, {:author => "Tolkien"}])
 Book.search(:and => [{:price => {:gt => 10}}, {:not => {:stock => 0}}, :or => [{:title => "Potter"}, {:author => "Rowling"}]])
 Book.search(:or => [{:query => "Rowling -Potter"}, {:query => "Tolkien -Rings"}])
+Book.search({:title => {:sql => ->(node, visitor) { "#{visitor.visit node.left} LIKE '%Rowl%'" }}})
 # ...
 ```
 

lib/search_cop/hash_parser.rb

@@ -31,9 +31,13 @@ def parse_attribute(key, value)
     collection = SearchCopGrammar::Attributes::Collection.new(query_info, key.to_s)
 
     if value.is_a?(Hash)
-      raise(SearchCop::ParseError, "Unknown operator #{value.keys.first}") unless [:matches, :eq, :not_eq, :gt, :gteq, :lt, :lteq].include?(value.keys.first)
+      raise(SearchCop::ParseError, "Unknown operator #{value.keys.first}") unless [:matches, :eq, :not_eq, :gt, :gteq, :lt, :lteq, :sql].include?(value.keys.first)
 
-      collection.send value.keys.first, value.values.first.to_s
+      if value.keys.first == :sql
+        collection.send value.keys.first, value.values.first
+      else
+        collection.send value.keys.first, value.values.first.to_s
+      end
     else
       collection.send :matches, value.to_s
     end

lib/search_cop/visitors/visitor.rb

@@ -55,6 +55,10 @@ def visit_SearchCopGrammar_Nodes_Not(node)
         "NOT (#{visit node.object})"
       end
 
+      def visit_SearchCopGrammar_Nodes_Sql(node)
+        node.right.call(node, self)
+      end
+
       def quote_table_name(name)
         connection.quote_table_name name
       end

lib/search_cop_grammar/attributes.rb

@@ -31,6 +31,12 @@ def hash
          end
       end
 
+      def sql(value)
+        attributes.collect! do |attribute|
+          SearchCopGrammar::Nodes::Sql.new(attribute, value)
+        end.inject(:or)
+      end
+
       def matches(value)
         if fulltext?
           SearchCopGrammar::Nodes::MatchesFulltext.new self, value.to_s

lib/search_cop_grammar/nodes.rb

@@ -73,6 +73,7 @@ class GreaterThanOrEqual < Binary; end
     class LessThan < Binary; end
     class LessThanOrEqual < Binary; end
     class Matches < Binary; end
+    class Sql < Binary; end
 
     class Not
       include Base

test/hash_test.rb

@@ -93,5 +93,18 @@ def test_lteq
     assert_includes results, expected
     refute_includes results, rejected
   end
+
+  def test_sql
+    expected = create(:product, :title => "Expected")
+    rejected = create(:product, :title => "Rejected")
+
+    sql_generator = lambda do |node, visitor|
+      "#{visitor.visit node.left} = 'Expected'"
+    end
+    results = Product.search(:title => { :sql => sql_generator })
+
+    assert_includes results, expected
+    refute_includes results, rejected
+  end
 end
 

test/visitor_test.rb

@@ -97,5 +97,14 @@ def test_fulltext_or
     assert_equal("(MATCH(`products`.`title`) AGAINST('(Query1) (Query2)' IN BOOLEAN MODE))", SearchCop::Visitors::Visitor.new(ActiveRecord::Base.connection).visit(node)) if ENV["DATABASE"] == "mysql"
     assert_equal("(to_tsvector('english', COALESCE(\"products\".\"title\", '')) @@ to_tsquery('english', '(''Query1'') | (''Query2'')'))", SearchCop::Visitors::Visitor.new(ActiveRecord::Base.connection).visit(node)) if ENV["DATABASE"] == "postgres"
   end
+
+  def test_sql
+    sql_generator = ->(node, visitor) do
+      "#{visitor.visit node.left} = SQL STRING"
+    end
+    node = SearchCopGrammar::Attributes::Collection.new(SearchCop::QueryInfo.new(Product, Product.search_scopes[:search]), "title").sql(sql_generator).optimize!
+
+    assert_equal "#{quote_table_name "products"}.#{quote_column_name "title"} = SQL STRING", SearchCop::Visitors::Visitor.new(ActiveRecord::Base.connection).visit(node)
+  end
 end