instance method
create_or_find_by
Ruby on Rails 7.2.3
Since v6.0.6Signature
create_or_find_by(attributes, &block)Attempts to create a record with the given attributes in a table that has a unique database constraint on one or several of its columns. If a row already exists with one or several of these unique constraints, the exception such an insertion would normally raise is caught, and the existing record with those attributes is found using #find_by!.
This is similar to #find_or_create_by, but tries to create the record first. As such it is better suited for cases where the record is most likely not to exist yet.
There are several drawbacks to #create_or_find_by, though:
-
The underlying table must have the relevant columns defined with unique database constraints.
-
A unique constraint violation may be triggered by only one, or at least less than all, of the given attributes. This means that the subsequent #find_by! may fail to find a matching record, which will then raise an
ActiveRecord::RecordNotFoundexception, rather than a record with the given attributes. -
While we avoid the race condition between SELECT -> INSERT from
#find_or_create_by, we actually have another race condition between INSERT -> SELECT, which can be triggered if a DELETE between those two statements is run by another client. But for most applications, that’s a significantly less likely condition to hit. -
It relies on exception handling to handle control flow, which may be marginally slower.
-
The primary key may auto-increment on each create, even if it fails. This can accelerate the problem of running out of integers, if the underlying table is still stuck on a primary key of type int (note: All Rails apps since 5.1+ have defaulted to bigint, which is not liable to this problem).
-
Columns with unique database constraints should not have uniqueness validations defined, otherwise
#createwill fail due to validation errors and #find_by will never be called.
This method will return a record if all given attributes are covered by unique constraints (unless the INSERT -> DELETE -> SELECT race condition is triggered), but if creation was attempted and failed due to validation errors it won’t be persisted, you get what #create returns in such situation.
Parameters
-
attributesreq -
blockblock
Source
# File activerecord/lib/active_record/relation.rb, line 266
def create_or_find_by(attributes, &block)
with_connection do |connection|
record = nil
transaction(requires_new: true) do
record = create(attributes, &block)
record._last_transaction_return_status || raise(ActiveRecord::Rollback)
end
record
rescue ActiveRecord::RecordNotUnique
if connection.transaction_open?
where(attributes).lock.find_by!(attributes)
else
find_by!(attributes)
end
end
end
Defined in activerecord/lib/active_record/relation.rb line 266
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Defined in ActiveRecord::Relation