InvalidCastException with Instant field (using NodaTime) when many database connections are open about efcore.pg

[roji]

Yes, that is unfortunately the expected behavior; if you use a simple connection string to configure EF, then at the lower Npgsql level the same connection pool is used, and the first time it's initialized (e.g. without NodaTime) is what takes effect for all subsequent use.

The right way forward here is to create two NpgsqlDataSource instances (see the docs) - one with NodaTime, and one without. Then, pass the correct NpgsqlDataSource to EF's UseNpgsql() instead of the connection string. This creates a simple, clear separation between usage/non-usage of NodaTime all the way down the stack.

Another workaround is to simply always turn on NodaTime. Even if you don't use it, it shouldn't interfere with regular DateTime usage.

Finally, you can use different connection strings to have separate connection pools at the lower Npgsql level (as you see to be doing in your demo project). That ensures having different pools, similar to what NpgsqlDataSource achieves, but in a hackier worse way.

I'll go ahead and close this issue as the behavior is by-design, but don't hesitate to post back with more questions etc. I can reopen as necessary.

[draudrau]

Thanks,

I tried this on one of my projects and it seems to work.
Added a data source in the services collection and reused it on health checks and DbContext.