EF Core DbContext Connection issue

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

References

• DbContext Lifetime, Configuration, and Initialization
• c# - How to avoid DbContext threading issues