Composite() function returns a private type, which should
be registered with ConnInfo.RegisterDataType for the composite
type's OID.
All subsequent interaction with Composite types is to be done
via Row(...) function. Function return value can be either
passed as a query argument to build SQL composite value out of
individual fields or passed to Scan to read SQL composite value
back.
When passed to Scan, Row() should have first argument of type
*bool to flag NULL values returned from query.
It was a mistake to use it in other contexts. This made interop
difficult between pacakges that depended on pgtype such as pgx and
packages that did not like pgconn and pgproto3. In particular this was
awkward for prepared statements.
Because pgx depends on pgtype and the tests for pgtype depend on pgx
this change will require a couple back and forth commits to get the
go.mod dependecies correct.
Instead of needing to instrospect the database on connection preload the
standard OID / type map. Types from extensions (like hstore) and custom
types can be registered by the application developer. Otherwise, they
will be treated as strings.
They now take ownership of the src argument.
Needed to change Scan to make a copy of []byte arguments as lib/pq apparently
gives Scan a shared memory buffer.
Because reading a record type requires the decoder to be able to look up oid
to type mapping and types such as hstore have types that are not fixed between
different PostgreSQL servers it was necessary to restructure the pgtype system
so all encoders and decodes take a *ConnInfo that includes oid/name/type
information.
Though this doesn't follow Go naming conventions exactly it makes names more
consistent with PostgreSQL and it is easier to read. For example, TIDOID becomes
TidOid. In addition this is one less breaking change in the move to V3.
