Support query-specific extensions in postgrex

[MSch]

There should be a way to enable certain extensions only for certain queries:

query("SELECT $1", ["=(integer, integer)"], extensions: [MyQuerySpecificExtension])

[josevalim]

I think this makes it very hard to cache. Can't you do it per connection?

[MSch]

Unfortunately not, the whole point is about having some extensions enabled only for some queries.

Isn't caching this as easy as adding the extensions to the cache key?

[ericmj]

It assumes that the postgres types the extension needs are already fetched and cached. This is specifically to override other extensions, if the extension adds new types it should just be added to the initial list of extensions.

If needed we can verify that the extension doesn't try to add new types.

[fishcakez]

As an alternative could you make use of encode_mapper/decode_mapper in #128? We can allow use of these in Ecto 2.0 as Ecto will need these.

[MSch]

My orginal use case was that I optionally wanted to send regclass/regname using text encoding, to make queries using them work like they do in psql or Rails. But I think the workaround described in the README works fine, and Postgrex even links the user to the documentation of this caveat when they run into this problem.

So from my side I don't have any use case for that feature any more.

[ericmj]

Since this becomes even more complicated with type caching I am closing this.