EF Core DbContext Connection issue
net | EF Core, Database, C# | 2021-08-20
Was working on .NET Core application using Entity Framework Core as ORM to database. The application consists of multiple DbContext, public / authorized RESTful API with JWT token authentication.
The request & response flow as below:
Request –>
JWT Middleware to grab user object –>
Authorization Filter to stop multiple login ->
Touch Controller ->
Repository ->
Execute Query ->
Response
Issue and Solution:
An exception occurred while **iterating over** the results of a query for context type.
The connection is closed
Check the through LINQ / Lambda query, make sure that has no second query holds queryable object before current queryable object has execute into a list or released.
$One or more errors occurred.
(A second operation started on this context before a previous operation completed.
This is usually caused by **different threads** using the same instance of DbContext.)
As we know EF Core does not support multiple parallel operations being run on the same DbContext instance
A few troubleshoots can carry out:
- Reduce frontend API calls by consolidating similar API into a single / fewer endpoints
- Make sure to await all async calls before continuing to use the context instance.
- Register DbContext as transient service
- Using IServiceScopeFactory for each thread