Discussion about -go-type

[aight8]

I noticed that the --pg-type maps a pg type to a destination go type. The go type have to implement the ValueTranscoder interface, which are quiet a lot functions.
Furthermore, a transcoder type cannot be reused.

Often (including pggen itself) has following mechanics:
pg type <-> transcoder type <-> destination go type

note: this is a view of the pgx.ConnInfo state with it's default data set + 2 registerd Composit Types
note: the light green "yes" is the default one - the dark green "yes" is implemented but not the default

What do you think to optionally define separate pgx type / destination types?

-go-type=pgtype=valuetype=assigntotype

[aight8]

When I handcraft the destination type I can also set the optional fields manually as pointer.
The only requirement is that the transcoder type fullfill one of the things:

• destination type is the same than the transcoder type (just assign it - the type must implement the full ValueTranscoder interface)
• destination type can be used as destination parameter in AssignTo for the used transcoder type
• ? investigate: pointer destination type? can AssignTo handle values and also pointers...?

[jschaf]

What do you think to optionally define separate pgx type / destination types?

I think this implemented in 0056cfb. I still need to test the type override logic but it should work.

You can now do:

	q := NewQuerierConfig(conn, QuerierConfig{DataTypes: []pgtype.DataType{
		{
			Value: MyTranscoder,
			Name:  "a_postgres_type",
		},
	}})

Then you can tweak MyTranscoder.assignTo to set fields however you want on structs. The next step is to a support customizing the output type. We don't need it for anything and we can support any type.

[aight8]

I don't get it. Why this is a runtime option?
The problem is when I assign a domain pg type (which is literally only a basic pg type with predefined options and validation) to a go type. Pggen try to initialize the "int" as scan destination, but it's not implement the whole pgx Value interface.