Commit d6be539b authored by Sean McGivern's avatar Sean McGivern

Merge branch 'bvl-codeowner-rules-model-ce' into 'master'

Adds helper for `find_or_create_by` in transaction

See merge request gitlab-org/gitlab-ce!24913
parents 5dc15b2a ccd8a9b2
Pipeline #46229216 failed with stages
in 54 minutes and 46 seconds
......@@ -6,4 +6,12 @@ class ApplicationRecord < ActiveRecord::Base
def self.id_in(ids)
where(id: ids)
end
def self.safe_find_or_create_by(*args)
transaction(requires_new: true) do
find_or_create_by(*args)
end
rescue ActiveRecord::RecordNotUnique
retry
end
end
......@@ -256,32 +256,12 @@ violation, for example.
Using transactions does not solve this problem.
The following pattern should be used to avoid the problem:
To solve this we've added the `ApplicationRecord.safe_find_or_create_by`.
```ruby
Project.transaction do
begin
User.find_or_create_by(username: "foo")
rescue ActiveRecord::RecordNotUnique
retry
end
end
```
If the above block is run inside a transaction and hits the race
condition, the transaction is aborted and we cannot simply retry (any
further queries inside the aborted transaction are going to fail). We
can employ [nested transactions](http://api.rubyonrails.org/classes/ActiveRecord/Transactions/ClassMethods.html#module-ActiveRecord::Transactions::ClassMethods-label-Nested+transactions)
here to only rollback the "inner transaction". Note that `requires_new: true` is required here.
This method can be used just as you would the normal
`find_or_create_by` but it wraps the call in a *new* transaction and
retries if it were to fail because of an
`ActiveRecord::RecordNotUnique` error.
```ruby
Project.transaction do
begin
User.transaction(requires_new: true) do
User.find_or_create_by(username: "foo")
end
rescue ActiveRecord::RecordNotUnique
retry
end
end
```
To be able to use this method, make sure the model you want to use
this on inherits from `ApplicationRecord`.
......@@ -10,4 +10,14 @@ describe ApplicationRecord do
expect(User.id_in(records.last(2).map(&:id))).to eq(records.last(2))
end
end
describe '#safe_find_or_create_by' do
it 'creates the user avoiding race conditions' do
expect(Suggestion).to receive(:find_or_create_by).and_raise(ActiveRecord::RecordNotUnique)
allow(Suggestion).to receive(:find_or_create_by).and_call_original
expect { Suggestion.safe_find_or_create_by(build(:suggestion).attributes) }
.to change { Suggestion.count }.by(1)
end
end
end
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