38 lines
1.1 KiB
Markdown
38 lines
1.1 KiB
Markdown
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# Iterating Tables In Batches
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Rails provides a method called `in_batches` that can be used to iterate over
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rows in batches. For example:
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```ruby
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User.in_batches(of: 10) do |relation|
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relation.update_all(updated_at: Time.now)
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end
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```
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Unfortunately this method is implemented in a way that is not very efficient,
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both query and memory usage wise.
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To work around this you can include the `EachBatch` module into your models,
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then use the `each_batch` class method. For example:
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```ruby
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class User < ActiveRecord::Base
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include EachBatch
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end
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User.each_batch(of: 10) do |relation|
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relation.update_all(updated_at: Time.now)
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end
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```
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This will end up producing queries such as:
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```
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User Load (0.7ms) SELECT "users"."id" FROM "users" WHERE ("users"."id" >= 41654) ORDER BY "users"."id" ASC LIMIT 1 OFFSET 1000
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(0.7ms) SELECT COUNT(*) FROM "users" WHERE ("users"."id" >= 41654) AND ("users"."id" < 42687)
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```
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The API of this method is similar to `in_batches`, though it doesn't support
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all of the arguments that `in_batches` supports. You should always use
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`each_batch` _unless_ you have a specific need for `in_batches`.
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