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Optimistic Concurrency Management in EntityFramework Core
A concurrency issue/conflict happens when two or more requests update the same object or the same entity instance. If we don’t control the concurrency conflicts, then whoever updates the database last will overwrite the other user’s changes. The concurrency conflicts are not rare and developers usually take two approaches to control concurrency, optimistically and/or pessimistically.
The pessimistic concurrency usually refers to preventing accidental data inconsistency in concurrent scenarios by using database locks. In this case, developers are sure that there is a very high probability that User A will try to update a data row at the same time when User B updates it. The database locks will ensure the updates are done one by one in order to prevent two updates from happening at the same time. The pessimistic concurrency control is rare nowadays. We can avoid it by carefully designing data models and database schema, decoupling the business modules by message queues or similar, utilizing distributed caches, and using other optimization techniques.
The optimistic concurrency, on the other hand, allows both User A and User B to update the same database record. However, before the change is persisted in a database, a concurrency exception will be raised if the labeled fields have different values from the existing ones in the database. In this case, either User A or User B will succeed in updating the record, and the failed user will receive an error message.
Entity Framework Core supports optimistic concurrency management. In this post, we will go over an example case and implement concurrency controls using a SQLite database. For other database providers, the implementation would be easier. The full example project can be found in this GitHub repository.
Without Concurrency Detection
Let’s consider an entity of type BankAccount as defined in the following code snippet. The overly simplified model tracks the ID and balance of the bank account and has credit/debit methods to update the account balance.
