Support batching using custom columns

Author: fatkodima

activerecord/CHANGELOG.md

@@ -1,3 +1,13 @@
+*   Support batching using custom columns.
+
+    ```ruby
+    Product.in_batches(cursor: [:shop_id, :id]) do |relation|
+      # do something with relation
+    end
+    ```
+
+    *fatkodima*
+
 *   Use SQLite `IMMEDIATE` transactions when possible.
 
     Transactions run against the SQLite3 adapter default to IMMEDIATE mode to improve concurrency support and avoid busy exceptions.

activerecord/lib/active_record/relation/batches.rb

@@ -5,7 +5,7 @@
 module ActiveRecord
   # = Active Record \Batches
   module Batches
-    ORDER_IGNORE_MESSAGE = "Scoped order is ignored, it's forced to be batch order."
+    ORDER_IGNORE_MESSAGE = "Scoped order is ignored, use :cursor with :order to configure custom order."
     DEFAULT_ORDER = :asc
 
     # Looping through a collection of records from the database
@@ -35,11 +35,13 @@ module Batches
     #
     # ==== Options
     # * <tt>:batch_size</tt> - Specifies the size of the batch. Defaults to 1000.
-    # * <tt>:start</tt> - Specifies the primary key value to start from, inclusive of the value.
-    # * <tt>:finish</tt> - Specifies the primary key value to end at, inclusive of the value.
+    # * <tt>:start</tt> - Specifies the cursor column value to start from, inclusive of the value.
+    # * <tt>:finish</tt> - Specifies the cursor column value to end at, inclusive of the value.
     # * <tt>:error_on_ignore</tt> - Overrides the application config to specify if an error should be raised when
     #   an order is present in the relation.
-    # * <tt>:order</tt> - Specifies the primary key order (can be +:asc+ or +:desc+ or an array consisting
+    # * <tt>:cursor</tt> - Specifies the column to use for batching (can be a column name or an array
+    #   of column names). Defaults to primary key.
+    # * <tt>:order</tt> - Specifies the cursor column order (can be +:asc+ or +:desc+ or an array consisting
     #   of :asc or :desc). Defaults to +:asc+.
     #
     #     class Order < ActiveRecord::Base
@@ -71,20 +73,25 @@ module Batches
     #
     # NOTE: Order can be ascending (:asc) or descending (:desc). It is automatically set to
     # ascending on the primary key ("id ASC").
-    # This also means that this method only works when the primary key is
+    # This also means that this method only works when the cursor column is
     # orderable (e.g. an integer or string).
     #
+    # NOTE: When using custom columns for batching, they should include at least one unique column
+    # (e.g. primary key) as a tiebreaker. Also, to reduce the likelihood of race conditions,
+    # all columns should be static (unchangeable after it was set).
+    #
     # NOTE: By its nature, batch processing is subject to race conditions if
     # other processes are modifying the database.
-    def find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, order: DEFAULT_ORDER, &block)
+    def find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, cursor: primary_key, order: DEFAULT_ORDER, &block)
       if block_given?
-        find_in_batches(start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, order: order) do |records|
+        find_in_batches(start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, cursor: cursor, order: order) do |records|
           records.each(&block)
         end
       else
-        enum_for(:find_each, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, order: order) do
+        enum_for(:find_each, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, cursor: cursor, order: order) do
           relation = self
-          apply_limits(relation, start, finish, build_batch_orders(order)).size
+          cursor = Array(cursor)
+          apply_limits(relation, cursor, start, finish, build_batch_orders(cursor, order)).size
         end
       end
     end
@@ -109,11 +116,13 @@ def find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, o
     #
     # ==== Options
     # * <tt>:batch_size</tt> - Specifies the size of the batch. Defaults to 1000.
-    # * <tt>:start</tt> - Specifies the primary key value to start from, inclusive of the value.
-    # * <tt>:finish</tt> - Specifies the primary key value to end at, inclusive of the value.
+    # * <tt>:start</tt> - Specifies the cursor column value to start from, inclusive of the value.
+    # * <tt>:finish</tt> - Specifies the cursor column value to end at, inclusive of the value.
     # * <tt>:error_on_ignore</tt> - Overrides the application config to specify if an error should be raised when
     #   an order is present in the relation.
-    # * <tt>:order</tt> - Specifies the primary key order (can be +:asc+ or +:desc+ or an array consisting
+    # * <tt>:cursor</tt> - Specifies the column to use for batching (can be a column name or an array
+    #   of column names). Defaults to primary key.
+    # * <tt>:order</tt> - Specifies the cursor column order (can be +:asc+ or +:desc+ or an array consisting
     #   of :asc or :desc). Defaults to +:asc+.
     #
     #     class Order < ActiveRecord::Base
@@ -140,21 +149,26 @@ def find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, o
     #
     # NOTE: Order can be ascending (:asc) or descending (:desc). It is automatically set to
     # ascending on the primary key ("id ASC").
-    # This also means that this method only works when the primary key is
+    # This also means that this method only works when the cursor column is
     # orderable (e.g. an integer or string).
     #
+    # NOTE: When using custom columns for batching, they should include at least one unique column
+    # (e.g. primary key) as a tiebreaker. Also, to reduce the likelihood of race conditions,
+    # all columns should be static (unchangeable after it was set).
+    #
     # NOTE: By its nature, batch processing is subject to race conditions if
     # other processes are modifying the database.
-    def find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, order: DEFAULT_ORDER)
+    def find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, cursor: primary_key, order: DEFAULT_ORDER)
       relation = self
       unless block_given?
-        return to_enum(:find_in_batches, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, order: order) do
-          total = apply_limits(relation, start, finish, build_batch_orders(order)).size
+        return to_enum(:find_in_batches, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, cursor: cursor, order: order) do
+          cursor = Array(cursor)
+          total = apply_limits(relation, cursor, start, finish, build_batch_orders(cursor, order)).size
           (total - 1).div(batch_size) + 1
         end
       end
 
-      in_batches(of: batch_size, start: start, finish: finish, load: true, error_on_ignore: error_on_ignore, order: order) do |batch|
+      in_batches(of: batch_size, start: start, finish: finish, load: true, error_on_ignore: error_on_ignore, cursor: cursor, order: order) do |batch|
         yield batch.to_a
       end
     end
@@ -183,11 +197,13 @@ def find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore:
     # ==== Options
     # * <tt>:of</tt> - Specifies the size of the batch. Defaults to 1000.
     # * <tt>:load</tt> - Specifies if the relation should be loaded. Defaults to false.
-    # * <tt>:start</tt> - Specifies the primary key value to start from, inclusive of the value.
-    # * <tt>:finish</tt> - Specifies the primary key value to end at, inclusive of the value.
+    # * <tt>:start</tt> - Specifies the cursor column value to start from, inclusive of the value.
+    # * <tt>:finish</tt> - Specifies the cursor column value to end at, inclusive of the value.
     # * <tt>:error_on_ignore</tt> - Overrides the application config to specify if an error should be raised when
     #   an order is present in the relation.
-    # * <tt>:order</tt> - Specifies the primary key order (can be +:asc+ or +:desc+ or an array consisting
+    # * <tt>:cursor</tt> - Specifies the column to use for batching (can be a column name or an array
+    #   of column names). Defaults to primary key.
+    # * <tt>:order</tt> - Specifies the cursor column order (can be +:asc+ or +:desc+ or an array consisting
     #   of :asc or :desc). Defaults to +:asc+.
     #
     #     class Order < ActiveRecord::Base
@@ -231,18 +247,21 @@ def find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore:
     #
     # NOTE: Order can be ascending (:asc) or descending (:desc). It is automatically set to
     # ascending on the primary key ("id ASC").
-    # This also means that this method only works when the primary key is
+    # This also means that this method only works when the cursor column is
     # orderable (e.g. an integer or string).
     #
+    # NOTE: When using custom columns for batching, they should include at least one unique column
+    # (e.g. primary key) as a tiebreaker. Also, to reduce the likelihood of race conditions,
+    # all columns should be static (unchangeable after it was set).
+    #
     # NOTE: By its nature, batch processing is subject to race conditions if
     # other processes are modifying the database.
-    def in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore: nil, order: DEFAULT_ORDER, use_ranges: nil, &block)
-      unless Array(order).all? { |ord| [:asc, :desc].include?(ord) }
-        raise ArgumentError, ":order must be :asc or :desc or an array consisting of :asc or :desc, got #{order.inspect}"
-      end
+    def in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore: nil, cursor: primary_key, order: DEFAULT_ORDER, use_ranges: nil, &block)
+      cursor = Array(cursor).map(&:to_s)
+      ensure_valid_options_for_batching!(cursor, start, finish, order)
 
       unless block
-        return BatchEnumerator.new(of: of, start: start, finish: finish, relation: self, order: order, use_ranges: use_ranges)
+        return BatchEnumerator.new(of: of, start: start, finish: finish, relation: self, cursor: cursor, order: order, use_ranges: use_ranges)
       end
 
       if arel.orders.present?
@@ -261,6 +280,7 @@ def in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore:
           relation: self,
           start: start,
           finish: finish,
+          cursor: cursor,
           order: order,
           batch_limit: batch_limit,
           &block
@@ -271,6 +291,7 @@ def in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore:
           start: start,
           finish: finish,
           load: load,
+          cursor: cursor,
           order: order,
           use_ranges: use_ranges,
           remaining: remaining,
@@ -281,28 +302,51 @@ def in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore:
     end
 
     private
-      def apply_limits(relation, start, finish, batch_orders)
-        relation = apply_start_limit(relation, start, batch_orders) if start
-        relation = apply_finish_limit(relation, finish, batch_orders) if finish
+      def ensure_valid_options_for_batching!(cursor, start, finish, order)
+        if start && Array(start).size != cursor.size
+          raise ArgumentError, ":start must contain one value per cursor column"
+        end
+
+        if finish && Array(finish).size != cursor.size
+          raise ArgumentError, ":finish must contain one value per cursor column"
+        end
+
+        if (Array(primary_key) - cursor).any?
+          indexes = model.schema_cache.indexes(table_name)
+          unique_index = indexes.find { |index| index.unique && index.where.nil? && (Array(index.columns) - cursor).empty? }
+
+          unless unique_index
+            raise ArgumentError, ":cursor must include a primary key or other unique column(s)"
+          end
+        end
+
+        if (Array(order) - [:asc, :desc]).any?
+          raise ArgumentError, ":order must be :asc or :desc or an array consisting of :asc or :desc, got #{order.inspect}"
+        end
+      end
+
+      def apply_limits(relation, cursor, start, finish, batch_orders)
+        relation = apply_start_limit(relation, cursor, start, batch_orders) if start
+        relation = apply_finish_limit(relation, cursor, finish, batch_orders) if finish
         relation
       end
 
-      def apply_start_limit(relation, start, batch_orders)
+      def apply_start_limit(relation, cursor, start, batch_orders)
         operators = batch_orders.map do |_column, order|
           order == :desc ? :lteq : :gteq
         end
-        batch_condition(relation, primary_key, start, operators)
+        batch_condition(relation, cursor, start, operators)
       end
 
-      def apply_finish_limit(relation, finish, batch_orders)
+      def apply_finish_limit(relation, cursor, finish, batch_orders)
         operators = batch_orders.map do |_column, order|
           order == :desc ? :gteq : :lteq
         end
-        batch_condition(relation, primary_key, finish, operators)
+        batch_condition(relation, cursor, finish, operators)
       end
 
-      def batch_condition(relation, columns, values, operators)
-        cursor_positions = Array(columns).zip(Array(values), operators)
+      def batch_condition(relation, cursor, values, operators)
+        cursor_positions = cursor.zip(Array(values), operators)
 
         first_clause_column, first_clause_value, operator = cursor_positions.pop
         where_clause = predicate_builder[first_clause_column, first_clause_value, operator]
@@ -316,9 +360,9 @@ def batch_condition(relation, columns, values, operators)
         relation.where(where_clause)
       end
 
-      def build_batch_orders(order)
-        get_the_order_of_primary_key(order).map do |column, ord|
-          [column, ord || DEFAULT_ORDER]
+      def build_batch_orders(cursor, order)
+        cursor.zip(Array(order)).map do |column, order_|
+          [column, order_ || DEFAULT_ORDER]
         end
       end
 
@@ -332,23 +376,23 @@ def act_on_ignored_order(error_on_ignore)
         end
       end
 
-      def get_the_order_of_primary_key(order)
-        Array(primary_key).zip(Array(order))
-      end
-
-      def batch_on_loaded_relation(relation:, start:, finish:, order:, batch_limit:)
+      def batch_on_loaded_relation(relation:, start:, finish:, cursor:, order:, batch_limit:)
         records = relation.to_a
-        order = build_batch_orders(order).map(&:second)
+        order = build_batch_orders(cursor, order).map(&:second)
 
         if start || finish
           records = records.filter do |record|
-            (start.nil? || compare_values_for_order(record.id, start, order) >= 0) &&
-              (finish.nil? || compare_values_for_order(record.id, finish, order) <= 0)
+            values = record_cursor_values(record, cursor)
+
+            (start.nil? || compare_values_for_order(values, Array(start), order) >= 0) &&
+              (finish.nil? || compare_values_for_order(values, Array(finish), order) <= 0)
           end
         end
 
         records.sort! do |record1, record2|
-          compare_values_for_order(record1.id, record2.id, order)
+          values1 = record_cursor_values(record1, cursor)
+          values2 = record_cursor_values(record2, cursor)
+          compare_values_for_order(values1, values2, order)
         end
 
         records.each_slice(batch_limit) do |subrecords|
@@ -361,66 +405,65 @@ def batch_on_loaded_relation(relation:, start:, finish:, order:, batch_limit:)
         nil
       end
 
+      def record_cursor_values(record, cursor)
+        record.attributes.slice(*cursor).values
+      end
+
       # This is a custom implementation of `<=>` operator,
       # which also takes into account how the collection will be ordered.
-      def compare_values_for_order(value1, value2, order)
-        # Multiple column values.
-        if value1.is_a?(Array)
-          value1.each_with_index do |element1, index|
-            element2 = value2[index]
-            direction = order[index]
-            comparison = element1 <=> element2
-            comparison = -comparison if direction == :desc
-            return comparison if comparison != 0
-          end
-
-          0
-        # Single column values.
-        elsif order.first == :asc
-          value1 <=> value2
-        else
-          value2 <=> value1
+      def compare_values_for_order(values1, values2, order)
+        values1.each_with_index do |element1, index|
+          element2 = values2[index]
+          direction = order[index]
+          comparison = element1 <=> element2
+          comparison = -comparison if direction == :desc
+          return comparison if comparison != 0
         end
+
+        0
       end
 
-      def batch_on_unloaded_relation(relation:, start:, finish:, load:, order:, use_ranges:, remaining:, batch_limit:)
-        batch_orders = build_batch_orders(order)
+      def batch_on_unloaded_relation(relation:, start:, finish:, load:, cursor:, order:, use_ranges:, remaining:, batch_limit:)
+        batch_orders = build_batch_orders(cursor, order)
         relation = relation.reorder(batch_orders.to_h).limit(batch_limit)
-        relation = apply_limits(relation, start, finish, batch_orders)
+        relation = apply_limits(relation, cursor, start, finish, batch_orders)
         relation.skip_query_cache! # Retaining the results in the query cache would undermine the point of batching
         batch_relation = relation
         empty_scope = to_sql == model.unscoped.all.to_sql
 
         loop do
           if load
             records = batch_relation.records
-            ids = records.map(&:id)
-            yielded_relation = where(primary_key => ids)
+            values = records.pluck(*cursor)
+            yielded_relation = where(cursor => values)
             yielded_relation.load_records(records)
           elsif (empty_scope && use_ranges != false) || use_ranges
-            ids = batch_relation.ids
-            finish = ids.last
+            values = batch_relation.pluck(*cursor)
+
+            finish = values.last
             if finish
-              yielded_relation = apply_finish_limit(batch_relation, finish, batch_orders)
+              yielded_relation = apply_finish_limit(batch_relation, cursor, finish, batch_orders)
               yielded_relation = yielded_relation.except(:limit, :order)
               yielded_relation.skip_query_cache!(false)
             end
           else
-            ids = batch_relation.ids
-            yielded_relation = where(primary_key => ids)
+            values = batch_relation.pluck(*cursor)
+            yielded_relation = where(cursor => values)
           end
 
-          break if ids.empty?
+          break if values.empty?
 
-          primary_key_offset = ids.last
-          raise ArgumentError.new("Primary key not included in the custom select clause") unless primary_key_offset
+          if values.flatten.any?(nil)
+            raise ArgumentError, "Not all of the batch cursor columns were included in the custom select clause "\
+                                  "or some columns contain nil."
+          end
 
           yield yielded_relation
 
-          break if ids.length < batch_limit
+          break if values.length < batch_limit
 
           if limit_value
-            remaining -= ids.length
+            remaining -= values.length
 
             if remaining == 0
               # Saves a useless iteration when the limit is a multiple of the
@@ -438,7 +481,8 @@ def batch_on_unloaded_relation(relation:, start:, finish:, load:, order:, use_ra
           end
           operators << (last_order == :desc ? :lt : :gt)
 
-          batch_relation = batch_condition(relation, primary_key, primary_key_offset, operators)
+          cursor_value = values.last
+          batch_relation = batch_condition(relation, cursor, cursor_value, operators)
         end
 
         nil