Merge pull request #18909 from kbrock/fix_order

Allow order fields to be subqueries with order

lib/extensions/ar_order.rb

@@ -0,0 +1,39 @@
+# This monkey patches rails to support proper joins
+# current PR: https://github.com/rails/rails/pull/36531
+module ActiveRecord
+  module ConnectionAdapters
+    module PostgreSQL
+      module SchemaStatements
+        def columns_for_distinct(columns, orders) #:nodoc:
+          order_columns = orders.reject(&:blank?).map { |s|
+              # Convert Arel node to string
+              unless s.is_a?(String)
+                if s.kind_of?(Arel::Nodes::Ordering)
+                  s = s.expr
+                  keep_order = true
+                end
+                if s.respond_to?(:to_sql)
+                  s = s.to_sql
+                else # for Arel::Nodes::Attribute
+                  engine = Arel::Table.engine
+                  collector = Arel::Collectors::SQLString.new
+                  collector = engine.connection.visitor.accept s, collector
+                  s = collector.value
+                end
+              end
+              # If we haven't already removed the order clause,
+              # Remove any ASC/DESC modifiers
+              if keep_order
+                s
+              else
+                s.gsub(/\s+(?:ASC|DESC)\b/i, "")
+                 .gsub(/\s+NULLS\s+(?:FIRST|LAST)\b/i, "")
+              end
+            }.reject(&:blank?).map.with_index { |column, i| "#{column} AS alias_#{i}" }
+
+          (order_columns << super).join(", ")
+        end
+      end
+    end
+  end
+end

spec/lib/extensions/ar_order_spec.rb

@@ -0,0 +1,19 @@
+describe "ar_order extension" do
+  # includes a has_many AND references the has many
+  # this introduces a DISTINCT to the query.
+  # rails uses limited_ids_for (which calls columns_for_distinct) to run a quick query
+  #
+  # when we use a virtual attribute in the sort (and the attribute has a descending order)
+  # the string munging gives us issues.
+  it "supports order when distinct is present for has_many virtual column" do
+    expect do
+      VmOrTemplate.includes(:disks).references(:disks).order(:last_compliance_status).first
+    end.not_to raise_error
+  end
+
+  it "supports order when distinct is present for basic column" do
+    expect do
+      VmOrTemplate.includes(:disks).references(:disks).order(:id).first
+    end.not_to raise_error
+  end
+end