Merge pull request #12130 from egilburg/patch-1
Document a difference between pluck and select [ci skip]
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@ -1466,7 +1466,7 @@ Client.pluck(:id, :name)
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# => [[1, 'David'], [2, 'Jeremy'], [3, 'Jose']]
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```
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`pluck` makes it possible to replace code like
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`pluck` makes it possible to replace code like:
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```ruby
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Client.select(:id).map { |c| c.id }
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@ -1476,7 +1476,7 @@ Client.select(:id).map(&:id)
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Client.select(:id, :name).map { |c| [c.id, c.name] }
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```
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with
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with:
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```ruby
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Client.pluck(:id)
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@ -1484,6 +1484,37 @@ Client.pluck(:id)
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Client.pluck(:id, :name)
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```
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Unlike `select`, `pluck` directly converts a database result into a Ruby `Array`,
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without constructing `ActiveRecord` objects. This can mean better performance for
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a large or often-running query. However, any model method overrides will
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not be available. For example:
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```ruby
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class Client < ActiveRecord::Base
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def name
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"I am #{super}"
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end
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end
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Client.select(:name).map &:name
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# => ["I am David", "I am Jeremy", "I am Jose"]
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Client.pluck(:name)
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# => ["David", "Jeremy", "Jose"]
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```
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Furthermore, unlike `select` and other `Relation` scopes, `pluck` triggers an immediate
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query, and thus cannot be chained with any further scopes, although it can work with
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scopes already constructed earlier:
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```ruby
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Client.pluck(:name).limit(1)
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# => NoMethodError: undefined method `limit' for #<Array:0x007ff34d3ad6d8>
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Client.limit(1).pluck(:name)
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# => ["David"]
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```
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### `ids`
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`ids` can be used to pluck all the IDs for the relation using the table's primary key.
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