@luca-esse I haven't investigated #3107 or looked at this in any depth, but as the name suggests, NpgsqlOwnedJsonTypeMapping is used for owned entity mapping (the general EF support), and not when trying to map JsonElement properties (which are the Npgsql-specific, weakly-typed "DOM" way to map); see the docs for more info on these mapping methods.

@roji well, if you look at my issue, you will see that this is not the case unfortunately, the NpgsqlOwnedJsonTypeMapping is also used for the JsonElement properties, since you have commented out the original clrMapper for the JsonElement and put this one instead.

here is a blame to the commented out line

and this is the current mapping:
{ typeof(JsonElement), _jsonbOwned },

As you can see, now the jsonElement is mapped to the NpgsqlOwnedJsonTypeMapping and this breaks the migrations if this method is not implemented, as explained in my issue

This is not the case for example with the JsonDocument, which is still mapped to NpgsqlJsonTypeMapping and in fact it’s working fine

This is a significant regression that seriously affects the ability to use JsonElement.

It warrants a more thorough investigation to understand the full impact and find a viable solution.

dotnet/efcore#32192

@luca-esse @Laurianti I spent some time to investigate this, and posted my findings as #3107 (comment) - please take a look. @luca-esse you're right that adding literal generation to NpgsqlOwnedJsonTypeMapping (as this PR does) would work around the specific bug, but that goes even further in the (current) hacky direction, whereas we really need to clean this up properly instead. The workaround I posted (specifying the default SQL explicitly) seems reasonable until that happens.