Defer Arel attribute lookup to the model class

This still isn't as separated as I'd like, but it at least moves most of
the burden of alias mapping in one place.

activerecord/lib/active_record/associations/join_dependency/join_association.rb

@@ -75,7 +75,7 @@ def join_constraints(foreign_table, foreign_klass, node, join_type, tables, scop
               column = klass.columns_hash[reflection.type.to_s]
 
               binds << Relation::QueryAttribute.new(column.name, value, klass.type_for_attribute(column.name))
-              constraint = constraint.and table[reflection.type].eq(Arel::Nodes::BindParam.new)
+              constraint = constraint.and klass.arel_attribute(reflection.type, table).eq(Arel::Nodes::BindParam.new)
             end
 
             joins << table.create_join(table, table.create_on(constraint), join_type)

activerecord/lib/active_record/associations/preloader/association.rb

@@ -47,7 +47,7 @@ def association_key_name
         # This is overridden by HABTM as the condition should be on the foreign_key column in
         # the join table
         def association_key
-          table[association_key_name]
+          klass.arel_attribute(association_key_name, table)
         end
 
         # The name of the key on the model which declares the association

activerecord/lib/active_record/core.rb

@@ -256,6 +256,11 @@ def arel_engine # :nodoc:
           end
       end
 
+      def arel_attribute(name, table) # :nodoc:
+        name = attribute_alias(name) if attribute_alias?(name)
+        table[name]
+      end
+
       def predicate_builder # :nodoc:
         @predicate_builder ||= PredicateBuilder.new(table_metadata)
       end

activerecord/lib/active_record/inheritance.rb

@@ -192,7 +192,7 @@ def find_sti_class(type_name)
       end
 
       def type_condition(table = arel_table)
-        sti_column = table[inheritance_column]
+        sti_column = arel_attribute(inheritance_column, table)
         sti_names  = ([self] + descendants).map(&:sti_name)
 
         sti_column.in(sti_names)

activerecord/lib/active_record/relation.rb

@@ -47,7 +47,7 @@ def insert(values) # :nodoc:
 
         if !primary_key_value && connection.prefetch_primary_key?(klass.table_name)
           primary_key_value = connection.next_sequence_value(klass.sequence_name)
-          values[klass.arel_table[klass.primary_key]] = primary_key_value
+          values[klass.arel_attribute(klass.primary_key, table)] = primary_key_value
         end
       end
 
@@ -373,9 +373,9 @@ def update_all(updates)
       stmt.table(table)
 
       if joins_values.any?
-        @klass.connection.join_to_update(stmt, arel, table[primary_key])
+        @klass.connection.join_to_update(stmt, arel, @klass.arel_attribute(primary_key, table))
       else
-        stmt.key = table[primary_key]
+        stmt.key = @klass.arel_attribute(primary_key, table)
         stmt.take(arel.limit)
         stmt.order(*arel.orders)
         stmt.wheres = arel.constraints
@@ -527,7 +527,7 @@ def delete_all(conditions = nil)
         stmt.from(table)
 
         if joins_values.any?
-          @klass.connection.join_to_delete(stmt, arel, table[primary_key])
+          @klass.connection.join_to_delete(stmt, arel, @klass.arel_attribute(primary_key, table))
         else
           stmt.wheres = arel.constraints
         end

activerecord/lib/active_record/relation/batches.rb

@@ -204,15 +204,15 @@ def in_batches(of: 1000, start: nil, finish: nil, load: false)
         yield yielded_relation
 
         break if ids.length < of
-        batch_relation = relation.where(table[primary_key].gt(primary_key_offset))
+        batch_relation = relation.where(klass.arel_attribute(primary_key, table).gt(primary_key_offset))
       end
     end
 
     private
 
     def apply_limits(relation, start, finish)
-      relation = relation.where(table[primary_key].gteq(start)) if start
-      relation = relation.where(table[primary_key].lteq(finish)) if finish
+      relation = relation.where(klass.arel_attribute(primary_key, table).gteq(start)) if start
+      relation = relation.where(klass.arel_attribute(primary_key, table).lteq(finish)) if finish
       relation
     end
 

activerecord/lib/active_record/relation/calculations.rb

@@ -155,15 +155,7 @@ def calculate(operation, column_name)
     # See also #ids.
     #
     def pluck(*column_names)
-      column_names.map! do |column_name|
-        if column_name.is_a?(Symbol) && attribute_alias?(column_name)
-          attribute_alias(column_name)
-        else
-          column_name.to_s
-        end
-      end
-
-      if loaded? && (column_names - @klass.column_names).empty?
+      if loaded? && (column_names.map(&:to_s) - @klass.attribute_names - @klass.attribute_aliases.keys).empty?
         return @records.pluck(*column_names)
       end
 
@@ -172,7 +164,7 @@ def pluck(*column_names)
       else
         relation = spawn
         relation.select_values = column_names.map { |cn|
-          columns_hash.key?(cn) ? arel_table[cn] : cn
+          @klass.has_attribute?(cn) || @klass.attribute_alias?(cn) ? klass.arel_attribute(cn, table) : cn
         }
         result = klass.connection.select_all(relation.arel, nil, bound_attributes)
         result.cast_values(klass.attribute_types)

activerecord/lib/active_record/relation/finder_methods.rb

@@ -147,7 +147,7 @@ def first!
     def last(limit = nil)
       if limit
         if order_values.empty? && primary_key
-          order(arel_table[primary_key].desc).limit(limit).reverse
+          order(klass.arel_attribute(primary_key, table).desc).limit(limit).reverse
         else
           to_a.last(limit)
         end
@@ -514,7 +514,7 @@ def find_nth_with_limit(index, limit)
       # TODO: once the offset argument is removed from find_nth,
       # find_nth_with_limit_and_offset can be merged into this method
       relation = if order_values.empty? && primary_key
-                   order(arel_table[primary_key].asc)
+                   order(klass.arel_attribute(primary_key, table).asc)
                  else
                    self
                  end

activerecord/lib/active_record/relation/predicate_builder/relation_handler.rb

@@ -3,7 +3,7 @@ class PredicateBuilder
     class RelationHandler # :nodoc:
       def call(attribute, value)
         if value.select_values.empty?
-          value = value.select(value.klass.arel_table[value.klass.primary_key])
+          value = value.select(value.klass.arel_attribute(value.klass.primary_key, value.klass.arel_table))
         end
 
         attribute.in(value.arel)

activerecord/lib/active_record/relation/query_methods.rb

@@ -1093,8 +1093,8 @@ def build_select(arel)
 
     def arel_columns(columns)
       columns.map do |field|
-        if (Symbol === field || String === field) && columns_hash.key?(field.to_s) && !from_clause.value
-          arel_table[field]
+        if (Symbol === field || String === field) && (klass.has_attribute?(field) || klass.attribute_alias?(field)) && !from_clause.value
+          klass.arel_attribute(field, table)
         elsif Symbol === field
           connection.quote_table_name(field.to_s)
         else
@@ -1105,7 +1105,7 @@ def arel_columns(columns)
 
     def reverse_sql_order(order_query)
       if order_query.empty?
-        return [table[primary_key].desc] if primary_key
+        return [klass.arel_attribute(primary_key, table).desc] if primary_key
         raise IrreversibleOrderError,
           "Relation has no current order and table has no primary key to be used as default order"
       end
@@ -1170,12 +1170,10 @@ def preprocess_order_args(order_args)
       order_args.map! do |arg|
         case arg
         when Symbol
-          arg = klass.attribute_alias(arg) if klass.attribute_alias?(arg)
-          table[arg].asc
+          klass.arel_attribute(arg, table).asc
         when Hash
           arg.map { |field, dir|
-            field = klass.attribute_alias(field) if klass.attribute_alias?(field)
-            table[field].send(dir.downcase)
+            klass.arel_attribute(field, table).send(dir.downcase)
           }
         else
           arg

activerecord/lib/active_record/table_metadata.rb

@@ -22,7 +22,11 @@ def resolve_column_aliases(hash)
     end
 
     def arel_attribute(column_name)
-      arel_table[column_name]
+      if klass
+        klass.arel_attribute(column_name, arel_table)
+      else
+        arel_table[column_name]
+      end
     end
 
     def type(column_name)

activerecord/test/cases/relation/mutation_test.rb

@@ -26,6 +26,10 @@ def sanitize_sql(sql)
       def sanitize_sql_for_order(sql)
         sql
       end
+
+      def arel_attribute(name, table)
+        table[name]
+      end
     end
 
     def relation