Generate getter methods for query models

[Cyberax]

This change allows the use of face interfaces to write somewhat generic
mapping methods.

Example:

// An example of an application-level structure
type AppAuthor struct {
	ID   int64
	Name string
	Bio  string
}

// A mapper that uses a face interface
func MapToAuthor(a interface {
	GetID() int64
	GetName() string
	GetBio() sql.NullString
}) AppAuthor {
	return AppAuthor{
		ID:   a.GetID(),
		Name: a.GetName(),
		Bio:  a.GetBio().String,
	}
}

[kyleconroy]

@Cyberax I'm so sorry this PR has languished with a review. I was going to review it and then things got a bit crazy.

I'm not sold on the utility of these Getter methods. They also conflict other fields on the structs themselves. You can imagine a database table with a foo and get_foo column.

If you're looking for these type of interfaces, I'd suggest using a small amount of codegen to inspect the struct and generate the methods from that.

[Cyberax]

These "face interfaces" actually saved me quite a bit of code in mappers, because I have a fair amount of almost but not exactly the same queries.

I don't see any problems with foo and get_foo, you'll have methods GetFoo and GetGetFoo. This is admittedly ugly, but won't cause any issues.

I guess custom codegen is an option, but at least can you tags to generated classes so that they can be easily discovered?

[Cyberax]

Would you mind revisiting this PR? It would really help us (we're maintaining an internal fork for now).

[rf]

+1, this would be particularly useful for us as well for a similar reason!

[akshayjshah]

I'd also find this convenient, but I think it's reasonable to do with a separate code gen tool. Seems to me that there's enough complexity here already, especially for a personal project - cutting scope to keep the project semi-maintainable seems like a good long-term decision.

I don't see any problems with foo and get_foo, you'll have methods GetFoo and GetGetFoo. This is admittedly ugly, but won't cause any issues.

The problem is that the get_foo column will (by default) correspond to a GetFoo struct field, which conflicts with the GetFoo accessor for the foo column. See "Method declarations" in the Go spec: "If the base type is a struct type, the non-blank method and field names must be distinct." This exact issue creates some complexity in the protobuf and Apache Thrift compilers, both of which generate accessors.

(Also, 👋 @rf!)