I have a parent child entity relationship which is driven by a REST API. The payload contains data for both the parent and the child. The parent can have many children.
When the (child) payload is posted the API first checks if the parent exists (based solely on an ID value in the payload). If it does exist, that parent entity is assigned to an entityref field when the child entity is created. If the parent doesn't exist; it is created and the newly created parent is assigned to the child.
This works great.. until. It seems now that the API user is publishing multiple children with the same parent at the same time (I assume some sort of multi-threaded process). So the breakdown occurs when the first 2 children are created (at the "same time") and they both determine there is no existing parent; and then create duplicate parents.
Is there some Drupal db method that allows me to lock creation of a certain entity type; triggered by the first spot in the API code where the parent is to be created? I assume they are not exactly the same time; but they are within 1 second of each other and more precisely they are within the time it takes to create the first parent. Perhaps even a REST function to handle threaded calls?