MONGOID-5844 Fix counting bug in HABTM associations (backport to 9.0) #5951
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In certain situations, calling #size on a HABTM association will return the wrong count. This will happen if the association is initialized to a single element (forcing the _unloaded Criteria object to be scoped to that specific element) and then assigning an array of multiple (already-persisted) elements to the association, where one of the elements is the same element that already existed there. In this case, `_unloaded.count` will return 1, and then the _added array will have two previously-persisted records. Naive implementations will thus return either 1, or 3, rather than the correct answer of 2. To get the correct answer, it is necessary to add a filter condition to `_unloaded.count` that excludes the records in the `_added` array.
comandeo-mongo
approved these changes
Feb 6, 2025
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(backport to 9.0)
In certain situations, calling #size on a HABTM association will return the wrong count.
This will happen if the association is
initialized to a single element (forcing the _unloaded Criteria object to be scoped to that specific element) and then assigning an array of multiple (already-persisted) elements to the association, where one of the elements is the same element that already existed there.
In this case,
_unloaded.countwill return 1, and then the _added array will have two previously-persisted records. Naive implementations will thus return either 1, or 3, rather than the correct answer of 2. To get the correct answer, it is necessary to add a filter condition to_unloaded.countthat excludes the records in the_addedarray.