Add support for pgx

[kyleconroy]

Get out the trumpets and ready the 21-gun salute, lib/pq is deprecated (#470). This means it's time to support it's successor, pgx.

This will be the main tracking issue for pgx. It supersedes #28, as I have no intention of adding support for any additional PostgreSQL drivers beyond pgx.

[ldelossa]

We currently use PGX and its batching mechanism. Would be great if you keep pgx batching in mind while this unfolds.

[kyleconroy]

@ldelossa Do you have an example of the batching API? This is the first I've heard of it

[ldelossa]

@kyleconroy we wrap it a bit to handle variable sized input:
https://github.com/quay/claircore/blob/master/pkg/microbatch/microbatch.go

usage:
https://github.com/quay/claircore/blob/master/internal/indexer/postgres/indexpackage.go#L96

[powersjcb]

pgx is new to me, so I wanted to spend some time getting the driver working for the example in examples/booktest/postgresql/. Here's a quick diff of that: powersjcb#1

Some learnings:

• Several fields in pgtype do not implement MarshalJSON. (at least pgtype.Timestamp and pgtype.VarcharArray) So at first glance, it looks like fields wont be compatible with the emitjsontags feature of sqlc.
• Many fields need to be initialized and then have a value Set into them using the following signature (dst *Timestamp) Set(src interface{}) error. User application code will no longer be able to type check these inputs at compile time. For exampleerr := pgtype.Timestamp{}.Set("asdf") will compile without errors.

[maxhawkins]

Awesome!

It would be cool to support decoding composite types at some point. It's pretty tedious to implement DecodeBinary since you have to pull out every value from the pgtype.Record by hand. Since we know the schema that could be automated and save a lot of time.

[maxhawkins]

* Several fields in `pgtype` do not implement `MarshalJSON`. (at least `pgtype.Timestamp` and `pgtype.VarcharArray`) So at first glance, it looks like fields wont be compatible with the `emitjsontags` feature of sqlc.

In the booktest example at least, the available column uses timestamptz whose pgtype counterpart Timestamptz does support JSON. Regardless I'm not sure it's a problem that raw timestamps don't have a JSON encoding. JSON times always have a zone and Postgres timestamps are ambiguous about what zone they're in so there's no natural conversion.

[mvrhov]

Do you really need to support pgtype... There are a lot of times you don't need it.. and pointer to native type is enough. This also means that you can use the same struct through most application and there is no need to convert between db struct and "domain" struct. The onl conversion is then for viewing purposes.

[powersjcb]

Thanks for the feedback @mvrhov! I was able to get my test cases working with some native go types and the pgx driver interfaces.

Also, just discovered that sqlc only implements 1-dimensional array types, so that will help keep things simple. 👍

[johanbrandhorst]

I noticed we're still using pq.Array for postgres array type (e.g. TEXT[] becomes pq.Array([]string)). Is it possible for these types to map to the pgx types instead (i.e. TEXT[] becomes pgtype.TextArray)? I tried using an override and it didn't seem to work in 1.4.0.