Add table name to search query (thoughtbot#830)

* Add table name to search query

Problem: When default scopes with joins are used, the generated
search query can lead to ambiguity. For instance, the column
`id` may exist in two tables, which will lead to a SQL error when it is
impossible to decide which table to use.

Solution: Add `resource_class`'s `table_name` to the generated search
query. This ensures that the generated query produces the format
`table_name.id` instead of `id` in the where clause generated for the
search.

* Quote table and column name in search

Closes thoughtbot#829

lib/administrate/search.rb

@@ -21,7 +21,12 @@ def run
     delegate :resource_class, to: :resolver
 
     def query
-      search_attributes.map { |attr| "lower(#{attr}) LIKE ?" }.join(" OR ")
+      search_attributes.map do |attr|
+        table_name = ActiveRecord::Base.connection.
+          quote_table_name(resource_class.table_name)
+        attr_name = ActiveRecord::Base.connection.quote_column_name(attr)
+        "lower(#{table_name}.#{attr_name}) LIKE ?"
+      end.join(" OR ")
     end
 
     def search_terms

spec/lib/administrate/search_spec.rb

@@ -43,11 +43,12 @@ class User; end
 
     it "searches using lower() + LIKE for all searchable fields" do
       begin
-        class User; end
+        class User < ActiveRecord::Base; end
         resolver = double(resource_class: User, dashboard_class: MockDashboard)
         search = Administrate::Search.new(resolver, "test")
         expected_query = [
-          "lower(name) LIKE ? OR lower(email) LIKE ?",
+          "lower(\"users\".\"name\") LIKE ?"\
+          " OR lower(\"users\".\"email\") LIKE ?",
           "%test%",
           "%test%",
         ]