Namespace
Class
Methods
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)
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.
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: It's not possible to set the order. That is automatically set to ascending on the primary key (“id ASC”) to make the batch ordering work. 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.
📝 Source code
# File activerecord/lib/active_record/relation/batches.rb, line 67
def find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil)
if block_given?
find_in_batches(start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore) 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) do
relation = self
apply_limits(relation, start, finish).size
end
end
end
🔎 See on GitHub
find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil)
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.
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: It's not possible to set the order. That is automatically set to ascending on the primary key (“id ASC”) to make the batch ordering work. 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.
📝 Source code
# File activerecord/lib/active_record/relation/batches.rb, line 126
def find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil)
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) do
total = apply_limits(relation, start, finish).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) do |batch|
yield batch.to_a
end
end
🔎 See on GitHub
in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore: nil)
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.
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: It's not possible to set the order. That is automatically set to ascending on the primary key (“id ASC”) to make the batch ordering consistent. Therefore the primary key must be orderable, e.g. an integer or a string.
NOTE: By its nature, batch processing is subject to race conditions if other processes are modifying the database.
📝 Source code
# File activerecord/lib/active_record/relation/batches.rb, line 201
def in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore: nil)
relation = self
unless block_given?
return BatchEnumerator.new(of: of, start: start, finish: finish, relation: self)
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).limit(batch_limit)
relation = apply_limits(relation, start, finish)
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
attr = Relation::QueryAttribute.new(primary_key, primary_key_offset, klass.type_for_attribute(primary_key))
batch_relation = relation.where(arel_attribute(primary_key).gt(Arel::Nodes::BindParam.new(attr)))
end
end
🔎 See on GitHub