This is a summary about handling concurrency in Asp.Net Core.
A concurrency conflict occurs when one user displays an entity’s data in order to edit it, and then another user updates the same entity’s data before the first user’s change is written to the database. If you don’t enable the detection of such conflicts, whoever updates the database last overwrites the other user’s changes. In many applications, this risk is acceptable: if there are few users, or few updates, or if isn’t really critical if some changes are overwritten, the cost of programming for concurrency might outweigh the benefit. In that case, you don’t have to configure the application to handle concurrency conflicts.
Pessimistic concurrency (locking)
If your application does need to prevent accidental data loss in concurrency scenarios, one way to do that is to use database locks. This is called pessimistic concurrency. For example, before you read a row from a database, you request a lock for read-only or for update access. If you lock a row for update access, no other users are allowed to lock the row either for read-only or update access, because they would get a copy of data that’s in the process of being changed. If you lock a row for read-only access, others can also lock it for read-only access but not for update.
Managing locks has disadvantages. It can be complex to program. It requires significant database management resources, and it can cause performance problems as the number of users of an application increases. For these reasons, not all database management systems support pessimistic concurrency. Entity Framework Core provides no built-in support for it, and this tutorial doesn’t show you how to implement it.
The alternative to pessimistic concurrency is optimistic concurrency. Optimistic concurrency means allowing concurrency conflicts to happen, and then reacting appropriately if they do. For example, Jane visits the Department Edit page and changes the Budget amount for the English department from $350,000.00 to $0.00. At the nearly same time, John changes it as well. More on Microsoft Docs Handle Concurrency