EDIT: For the current status of the issue, skip to #4231 (comment)

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I'm having an issue implementing an Optimistic Concurrency library on an application that uses DRF to interact with the database. I'm trying to:

• Confirm that the behavior I'm seeing is attributable to DRF
• Confirm that this is the intended behavior
• Determine if there's any practical way to overcome this behavior

I recently added optimistic concurrency to my Django application. To save you the Wiki lookup:

• Every model has a version field
• When an editor edits an object, they get the version of the object they're editing
• When the editor saves the object, the included version number is compared to the database
• If the versions match, the editor updated the latest document and the save goes through
• If the versions don't match, we assume a "conflicting" edit was submitted between the time the editor loaded and saved so we reject the edit
• If the version is missing, we cannot do testing and should reject the edit

I had a legacy UI talking through DRF. The legacy UI did not handle version numbers. I expected this to cause concurrency errors, but it did not. If I understand the discussion in #3648 correctly:

• DRF merges the PUT with the existing record. This causes a missing version ID to be filled with the current database ID
• Since this always provides a match, omitting this variable will always break an optimistic concurrency system that communicates across DRF
• There are no easy options (like making the field "required") to ensure the data is submitted every time. (edit: you can workaround the issue by making it required as demonstrated in this comment)

Steps to reproduce

1. Setup an Optimistic Concurrency field on a model
2. Create a new instance and update several times (to ensure you no longer have a default version number)
3. Submit an update (PUT) through DRF excluding the version ID

Expected behavior

The missing version ID should not match the database and cause a concurrency issue.

Actual behavior

The missing version ID is filled by DRF with the current ID so the concurrency check passes.