increment_counter
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increment_counter(counter_name, id)
public
Increment a number field by one, usually representing a count.
This is used for caching aggregate values, so that they don’t need to be computed every time. For example, a DiscussionBoard may cache post_count and comment_count otherwise every time the board is shown it would have to run an SQL query to find how many posts and comments there are.
Attributes
- counter_name - The name of the field that should be incremented.
- id - The id of the object that should be incremented.
Examples
# Increment the post_count column for the record with an id of 5 DiscussionBoard.increment_counter(:post_count, 5)
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See also: ActiveRecord::Base#increment
This is a class-level method. For the instance-level equivalent see: ActiveRecord::Base#increment
item = Item.find(1) item.foo_count # => 0 Item.increment_counter(:foo_count, 1) item.foo_count # => 0 item.reload item.foo_count # => 1 item.increment(:foo_count) item.foo_count # => 2
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won't refresh updated_at
This will not cause :updated_at column to refresh, while ActiveRecord::Base#increment! would.
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The "instance-level equivalent" ActiveRecord::Base#increment is NOT atomic
Typically, you want to increment counters atomically, so the class method ActiveRecord::Base.increment_counter is the right choice.
Also, there is an issue with the increment example below as it does not save automatically:
item = Item.find(1) item.foo_count # => 0 item.increment(:foo_count) item.foo_count # => 1 item.reload item.foo_count # => 0 item.increment(:foo_count) item.save item.reload item.foo_count # => 1