Add ability to config PostgreSQL ORDER BY ... NULLS FIRST or NULLS LA…

…ST, close #1125

README.md

@@ -250,6 +250,20 @@ the order indicator arrow by passing `hide_indicator: true` in the sort link:
   default_order: { last_name: 'asc', first_name: 'desc' }) %>
 ```
 
+#### PostgreSQL's sort option
+
+The `NULLS FIRST` and `NULLS LAST` options can be used to determine whether nulls appear before or after non-null values in the sort ordering.
+
+You may want to configure it like this:
+
+```rb
+Ransack.configure do |c|
+  c.postgres_fields_sort_option = :nulls_first # or :nulls_last
+end
+```
+
+See this feature: https://www.postgresql.org/docs/13/queries-order.html
+
 ### Advanced Mode
 
 "Advanced" searches (ab)use Rails' nested attributes functionality in order to

lib/ransack/adapters/active_record/context.rb

@@ -42,6 +42,13 @@ def evaluate(search, opts = {})
               if scope_or_sort.is_a?(Symbol)
                 relation = relation.send(scope_or_sort)
               else
+                case Ransack.options[:postgres_fields_sort_option]
+                when :nulls_first
+                  scope_or_sort = scope_or_sort.direction == :asc ? "#{scope_or_sort.to_sql} NULLS FIRST" : "#{scope_or_sort.to_sql} NULLS LAST"
+                when :nulls_last
+                  scope_or_sort = scope_or_sort.direction == :asc ? "#{scope_or_sort.to_sql} NULLS LAST" : "#{scope_or_sort.to_sql} NULLS FIRST"
+                end
+
                 relation = relation.order(scope_or_sort)
               end
             end

lib/ransack/configuration.rb

@@ -33,7 +33,8 @@ def []=(key, value)
       :up_arrow => '▼'.freeze,
       :down_arrow => '▲'.freeze,
       :default_arrow => nil,
-      :sanitize_scope_args => true
+      :sanitize_scope_args => true,
+      :postgres_fields_sort_option => nil
     }
 
     def configure
@@ -141,6 +142,21 @@ def sanitize_custom_scope_booleans=(boolean)
       self.options[:sanitize_scope_args] = boolean
     end
 
+    # The `NULLS FIRST` and `NULLS LAST` options can be used to determine
+    # whether nulls appear before or after non-null values in the sort ordering.
+    #
+    # User may want to configure it like this:
+    #
+    # Ransack.configure do |c|
+    #   c.postgres_fields_sort_option = :nulls_first # or :nulls_last
+    # end
+    #
+    # See this feature: https://www.postgresql.org/docs/13/queries-order.html
+    #
+    def postgres_fields_sort_option=(setting)
+      self.options[:postgres_fields_sort_option] = setting
+    end
+
     # By default, Ransack displays sort order indicator arrows in sort links.
     # The default may be globally overridden in an initializer file like
     # `config/initializers/ransack.rb` as follows:

spec/ransack/configuration_spec.rb

@@ -173,5 +173,15 @@ module Ransack
         .to eq false
       end
     end
+
+    it "PG's sort option", if: ::ActiveRecord::Base.connection.adapter_name == "PostgreSQL" do
+      default = Ransack.options.clone
+
+      Ransack.configure { |c| c.postgres_fields_sort_option = :nulls_first }
+
+      expect(Ransack.options[:postgres_fields_sort_option]).to eq :nulls_first
+
+      Ransack.options = default
+    end
   end
 end

spec/ransack/search_spec.rb

@@ -507,6 +507,27 @@ def remove_quotes_and_backticks(str)
         @s.sorts = 'id asc'
         expect(@s.result.first.id).to eq 1
       end
+
+      it "PG's sort option", if: ::ActiveRecord::Base.connection.adapter_name == "PostgreSQL" do
+        default = Ransack.options.clone
+
+        s = Search.new(Person, s: 'name asc')
+        expect(s.result.to_sql).to eq "SELECT \"people\".* FROM \"people\" ORDER BY \"people\".\"name\" ASC"
+
+        Ransack.configure { |c| c.postgres_fields_sort_option = :nulls_first }
+        s = Search.new(Person, s: 'name asc')
+        expect(s.result.to_sql).to eq "SELECT \"people\".* FROM \"people\" ORDER BY \"people\".\"name\" ASC NULLS FIRST"
+        s = Search.new(Person, s: 'name desc')
+        expect(s.result.to_sql).to eq "SELECT \"people\".* FROM \"people\" ORDER BY \"people\".\"name\" DESC NULLS LAST"
+
+        Ransack.configure { |c| c.postgres_fields_sort_option = :nulls_last }
+        s = Search.new(Person, s: 'name asc')
+        expect(s.result.to_sql).to eq "SELECT \"people\".* FROM \"people\" ORDER BY \"people\".\"name\" ASC NULLS LAST"
+        s = Search.new(Person, s: 'name desc')
+        expect(s.result.to_sql).to eq "SELECT \"people\".* FROM \"people\" ORDER BY \"people\".\"name\" DESC NULLS FIRST"
+
+        Ransack.options = default
+      end
     end
 
     describe '#method_missing' do