Constants
ORDER_IGNORE_MESSAGE | = | "Scoped order is ignored, it's forced to be batch order." |
Instance Public methods
find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, order: :asc) Link
Looping through a collection of records from the database (using the Scoping::Named::ClassMethods.all
method, for example) is very inefficient since it will try to instantiate all the objects at once.
In that case, batch processing methods allow you to work with the records in batches, thereby greatly reducing memory consumption.
The find_each
method uses find_in_batches
with a batch size of 1000 (or as specified by the :batch_size
option).
Person.find_each do |person|
person.do_awesome_stuff
end
Person.where("age > 21").find_each do |person|
person.party_all_night!
end
If you do not provide a block to find_each
, it will return an Enumerator for chaining with other methods:
Person.find_each.with_index do |person, index|
person.award_trophy(index + 1)
end
Options
-
:batch_size
- Specifies the size of the batch. Defaults to 1000. -
:start
- Specifies the primary key value to start from, inclusive of the value. -
:finish
- Specifies the primary key value to end at, inclusive of the value. -
:error_on_ignore
- Overrides the application config to specify if an error should be raised when an order is present in the relation. -
:order
- Specifies the primary key order (can be :asc or :desc). Defaults to :asc.
Limits are honored, and if present there is no requirement for the batch size: it can be less than, equal to, or greater than the limit.
The options start
and finish
are especially useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the records between id 1 and 9999 and worker 2 handle from 10000 and beyond by setting the :start
and :finish
option on each worker.
# In worker 1, let's process until 9999 records.
Person.find_each(finish: 9_999) do |person|
person.party_all_night!
end
# In worker 2, let's process from record 10_000 and onwards.
Person.find_each(start: 10_000) do |person|
person.party_all_night!
end
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 orderable (e.g. an integer or string).
NOTE: By its nature, batch processing is subject to race conditions if other processes are modifying the database.
# File activerecord/lib/active_record/relation/batches.rb, line 68 def find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, order: :asc) if block_given? find_in_batches(start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, order: order) do |records| records.each { |record| yield record } end else enum_for(:find_each, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, order: order) do relation = self apply_limits(relation, start, finish, order).size end end end
find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, order: :asc) Link
Yields each batch of records that was found by the find options as an array.
Person.where("age > 21").find_in_batches do |group|
sleep(50) # Make sure it doesn't get too crowded in there!
group.each { |person| person.party_all_night! }
end
If you do not provide a block to find_in_batches
, it will return an Enumerator for chaining with other methods:
Person.find_in_batches.with_index do |group, batch|
puts "Processing group ##{batch}"
group.each(&:recover_from_last_night!)
end
To be yielded each record one by one, use find_each
instead.
Options
-
:batch_size
- Specifies the size of the batch. Defaults to 1000. -
:start
- Specifies the primary key value to start from, inclusive of the value. -
:finish
- Specifies the primary key value to end at, inclusive of the value. -
:error_on_ignore
- Overrides the application config to specify if an error should be raised when an order is present in the relation. -
:order
- Specifies the primary key order (can be :asc or :desc). Defaults to :asc.
Limits are honored, and if present there is no requirement for the batch size: it can be less than, equal to, or greater than the limit.
The options start
and finish
are especially useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the records between id 1 and 9999 and worker 2 handle from 10000 and beyond by setting the :start
and :finish
option on each worker.
# Let's process from record 10_000 on.
Person.find_in_batches(start: 10_000) do |group|
group.each { |person| person.party_all_night! }
end
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 orderable (e.g. an integer or string).
NOTE: By its nature, batch processing is subject to race conditions if other processes are modifying the database.
# File activerecord/lib/active_record/relation/batches.rb, line 128 def find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, order: :asc) 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, 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| yield batch.to_a end end
in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore: nil, order: :asc) Link
Yields ActiveRecord::Relation
objects to work with a batch of records.
Person.where("age > 21").in_batches do |relation|
relation.delete_all
sleep(10) # Throttle the delete queries
end
If you do not provide a block to in_batches
, it will return a BatchEnumerator
which is enumerable.
Person.in_batches.each_with_index do |relation, batch_index|
puts "Processing relation ##{batch_index}"
relation.delete_all
end
Examples of calling methods on the returned BatchEnumerator
object:
Person.in_batches.delete_all
Person.in_batches.update_all(awesome: true)
Person.in_batches.each_record(&:party_all_night!)
Options
-
:of
- Specifies the size of the batch. Defaults to 1000. -
:load
- Specifies if the relation should be loaded. Defaults to false. -
:start
- Specifies the primary key value to start from, inclusive of the value. -
:finish
- Specifies the primary key value to end at, inclusive of the value. -
:error_on_ignore
- Overrides the application config to specify if an error should be raised when an order is present in the relation. -
:order
- Specifies the primary key order (can be :asc or :desc). Defaults to :asc.
Limits are honored, and if present there is no requirement for the batch size, it can be less than, equal, or greater than the limit.
The options start
and finish
are especially useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the records between id 1 and 9999 and worker 2 handle from 10000 and beyond by setting the :start
and :finish
option on each worker.
# Let's process from record 10_000 on.
Person.in_batches(start: 10_000).update_all(awesome: true)
An example of calling where query method on the relation:
Person.in_batches.each do |relation|
relation.update_all('age = age + 1')
relation.where('age > 21').update_all(should_party: true)
relation.where('age <= 21').delete_all
end
NOTE: If you are going to iterate through each record, you should call each_record on the yielded BatchEnumerator:
Person.in_batches.each_record(&:party_all_night!)
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 orderable (e.g. an integer or string).
NOTE: By its nature, batch processing is subject to race conditions if other processes are modifying the database.
# File activerecord/lib/active_record/relation/batches.rb, line 204 def in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore: nil, order: :asc) relation = self unless block_given? return BatchEnumerator.new(of: of, start: start, finish: finish, relation: self) end unless [:asc, :desc].include?(order) raise ArgumentError, ":order must be :asc or :desc, got #{order.inspect}" end if arel.orders.present? act_on_ignored_order(error_on_ignore) end batch_limit = of if limit_value remaining = limit_value batch_limit = remaining if remaining < batch_limit end relation = relation.reorder(batch_order(order)).limit(batch_limit) relation = apply_limits(relation, start, finish, order) relation.skip_query_cache! # Retaining the results in the query cache would undermine the point of batching batch_relation = relation loop do if load records = batch_relation.records ids = records.map(&:id) yielded_relation = where(primary_key => ids) yielded_relation.load_records(records) else ids = batch_relation.pluck(primary_key) yielded_relation = where(primary_key => ids) end break if ids.empty? primary_key_offset = ids.last raise ArgumentError.new("Primary key not included in the custom select clause") unless primary_key_offset yield yielded_relation break if ids.length < batch_limit if limit_value remaining -= ids.length if remaining == 0 # Saves a useless iteration when the limit is a multiple of the # batch size. break elsif remaining < batch_limit relation = relation.limit(remaining) end end batch_relation = relation.where( predicate_builder[primary_key, primary_key_offset, order == :desc ? :lt : :gt] ) end end