How that we’ve covered flow bulkification and flow interviews, we can tie things together. As mentioned, sometimes Salesforce automagically bulkifies flow interviews.
Most of the time, this is a good thing. Sometimes it’s not so good.
For example, imagine a flow that gets and updates a custom setting. Perhaps you store the last number used for a specific activity (like a counter).
When flow interviews are bulkified, then the last number will not always be reflected in each flow interview. For example, say Custom Setting.Last Number Used = 10. Then
- Flow interview A gets this value, sees 10, and then increments it to 11
- Flow interview B also gets this value, also sees 10, and also increments it to 11
If flows interviews were not bulkified, then Flow interview B also would see 11 instead of 10. But since they are bulkified, they are essentially running at the same time and see the same value.
So how do you prevent this from happening?
One answer is record locking. You call an invocable apex action from your flow. In the apex, you get the field and specify to lock the record until the transaction has ended (Details coming tomorrow).
Note: One drawback of this approach is you may come across the error, “The record you are attempting to edit, or one of its related records, is currently being modified by another user”
The takeaway
When you don’t want Salesforce to bulkify flows interviews, you only have a few options. One of them is to use record locking in apex.