Update active_record_callbacks.md [ci skip]

[sharang-d]

Change 'happen' to a more technical term

[sharang-d]

We can also say 'run' instead of 'execute' as we've used on another line.

[vipulnsward]

Thanks, both work better in different sentences. Can keep as is

[kamipo]

I don't think this should be merged. We already use "happen" a lots for callbacks and validations.

rails/activemodel/lib/active_model/validations/absence.rb

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	# Validates that the specified attributes are blank (as defined by
	# Object#blank?). Happens by default on save.

rails/activemodel/lib/active_model/validations/presence.rb

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	# Validates that the specified attributes are not blank (as defined by
	# Object#blank?). Happens by default on save.

rails/activerecord/lib/active_record/transactions.rb

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	# {#destroy}[rdoc-ref:Persistence#destroy] come wrapped in a transaction that ensures
	# that whatever you do in validations or callbacks will happen under its
	# protected cover. So you can use validations to check for values that

rails/guides/source/active_record_validations.md

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### When Does Validation Happen?

rails/guides/source/active_record_validations.md

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	The validation happens by performing an SQL query into the model's table,
	searching for an existing record with the same value in that attribute.

rails/guides/source/active_record_validations.md

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	validates :name, uniqueness: { scope: :year,
	message: "should happen once per year" }

rails/guides/source/active_record_validations.md

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The `:on` option lets you specify when the validation should happen. The

rails/guides/source/active_record_validations.md

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	option when you want to specify when the validation **should** happen. If you
	want to specify when the validation **should not** happen, then you may use the
	`:unless` option.

rails/guides/source/active_record_validations.md

Lines 921 to 922 in 02e6abd

	You can associate the `:if` and `:unless` options with a symbol corresponding
	to the name of a method that will get called right before validation happens.

rails/guides/source/active_record_validations.md

Lines 975 to 977 in 02e6abd

	On the other hand, when multiple conditions define whether or not a validation
	should happen, an `Array` can be used. Moreover, you can apply both `:if` and
	`:unless` to the same validation.

[kamipo]

Reverted 30016df for now.

[vipulnsward]

We already use "happen" a lots for callbacks and validations.

I see we use it for validations. For callbacks though, it just felt unnatural to read it that way, given its more referred to as "callback execution".

Before merging, I tried searching if "callback happening" is a normal term to used anywhere, did not find many examples.

Anyway happy to leave as is for now though.