AR's distinct compatible with 4.x (and 3.x) for Oracle, Derby and Postgres

Author: kares

lib/arjdbc/derby/adapter.rb

@@ -342,20 +342,28 @@ def rename_column(table_name, column_name, new_column_name)
     # @note This is based on distinct method for the PostgreSQL Adapter.
     # @override
     def distinct(columns, order_by)
-      return "DISTINCT #{columns}" if order_by.blank?
-
-      # construct a clean list of column names from the ORDER BY clause, removing
-      # any asc/desc modifiers
-      order_columns = [ order_by ].flatten!
-      order_columns.map! do |o|
-        o.split(',').collect! { |s| s.split.first }
-      end # .flatten!
+      "DISTINCT #{columns_for_distinct(columns, order_by)}"
+    end
+
+    # @override Since AR 4.0 (on 4.1 {#distinct} is gone and won't be called).
+    def columns_for_distinct(columns, orders)
+      return columns if orders.blank?
+
+      # construct a clean list of column names from the ORDER BY clause,
+      # removing any ASC/DESC modifiers
+      order_columns = [ orders ]; order_columns.flatten! # AR 3.x vs 4.x
+      order_columns.map! do |column|
+        column = column.to_sql unless column.is_a?(String) # handle AREL node
+        column.split(',').collect! { |s| s.split.first }
+      end.flatten!
       order_columns.reject!(&:blank?)
-      order_columns = order_columns.zip((0...order_columns.size).to_a).map { |s, i| "#{s} AS alias_#{i}" }
+      order_columns = order_columns.zip (0...order_columns.size).to_a
+      order_columns = order_columns.map { |s, i| "#{s} AS alias_#{i}" }
 
-      # return a DISTINCT clause that's distinct on the columns we want but includes
-      # all the required columns for the ORDER BY to work properly
-      "DISTINCT #{columns}, #{order_columns * ', '}"
+      columns = [ columns ]; columns.flatten!
+      columns.push( *order_columns ).join(', ')
+      # return a DISTINCT clause that's distinct on the columns we want but
+      # includes all the required columns for the ORDER BY to work properly
     end
 
     # @override

lib/arjdbc/oracle/adapter.rb

@@ -295,16 +295,27 @@ def remove_column(table_name, *column_names)
     # making every row the same.
     #
     #   distinct("posts.id", "posts.created_at desc")
+    #
+    # @override
     def distinct(columns, order_by)
-      return "DISTINCT #{columns}" if order_by.blank?
+      "DISTINCT #{columns_for_distinct(columns, order_by)}"
+    end
 
+    # @override Since AR 4.0 (on 4.1 {#distinct} is gone and won't be called).
+    def columns_for_distinct(columns, orders)
+      return columns if orders.blank?
+      if orders.is_a?(Array) # AR 3.x vs 4.x
+        orders = orders.map { |column| column.is_a?(String) ? column : column.to_sql }
+      else
+        orders = extract_order_columns(orders)
+      end
       # construct a valid DISTINCT clause, ie. one that includes the ORDER BY columns, using
       # FIRST_VALUE such that the inclusion of these columns doesn't invalidate the DISTINCT
-      order_columns = extract_order_columns(order_by).map do |c, i|
+      order_columns = orders.map do |c, i|
         "FIRST_VALUE(#{c.split.first}) OVER (PARTITION BY #{columns} ORDER BY #{c}) AS alias_#{i}__"
       end
-      sql = "DISTINCT #{columns}, "
-      sql << order_columns * ", "
+      columns = [ columns ]; columns.flatten!
+      columns.push( *order_columns ).join(', ')
     end
 
     # ORDER BY clause for the passed order option.

lib/arjdbc/postgresql/adapter.rb

@@ -747,29 +747,28 @@ def multi_column_index_limit=(limit)
       @multi_column_index_limit = limit
     end
 
-    # Returns a SELECT DISTINCT clause for a given set of columns and a given
-    # ORDER BY clause.
-    #
+    # @override
+    def distinct(columns, orders)
+      "DISTINCT #{columns_for_distinct(columns, orders)}"
+    end
+
     # PostgreSQL requires the ORDER BY columns in the select list for distinct
     # queries, and requires that the ORDER BY include the distinct column.
-    #
-    # distinct("posts.id", ["posts.created_at desc"])
-    # # => "DISTINCT posts.id, posts.created_at AS alias_0"
-    def distinct(columns, orders)
+    # @override Since AR 4.0 (on 4.1 {#distinct} is gone and won't be called).
+    def columns_for_distinct(columns, orders)
       if orders.is_a?(String)
         orders = orders.split(','); orders.each(&:strip!)
       end
 
-      order_columns = orders.map do |column|
+      order_columns = orders.reject(&:blank?).map! do |column|
         column = column.to_sql unless column.is_a?(String) # handle AREL node
         column.gsub(/\s+(ASC|DESC)\s*(NULLS\s+(FIRST|LAST)\s*)?/i, '') # remove ASC/DESC
-      end.reject(&:blank?)
-
-      return "DISTINCT #{columns}" if order_columns.empty?
-
+      end
+      order_columns.reject!(&:blank?)
       i = -1; order_columns.map! { |c| "#{c} AS alias_#{i += 1}" }
 
-      "DISTINCT #{columns}, #{order_columns.join(', ')}"
+      columns = [ columns ]; columns.flatten!
+      columns.push( *order_columns ).join(', ')
     end
 
     # ORDER BY clause for the passed order option.