database/sql: add NullInt16 support

[kyleconroy]

Hey Go team!

I maintain a database code generator. I'm having trouble correctly supporting null smallint columns because the database/sql package does not have a NullInt16 type. It would look almost identical to Nullint32 and NullInt64.

// NullInt16 represents an int32 that may be null.
// NullInt16 implements the Scanner interface so
// it can be used as a scan destination, similar to NullString.
type NullInt16 struct {
	Int16 int16
	Valid bool // Valid is true if Int16 is not NULL
}

// Scan implements the Scanner interface.
func (n *NullInt16) Scan(value interface{}) error {
	if value == nil {
		n.Int16, n.Valid = 0, false
		return nil
	}
	n.Valid = true
	return convertAssign(&n.Int16, value)
}

// Value implements the driver Valuer interface.
func (n NullInt16) Value() (driver.Value, error) {
	if !n.Valid {
		return nil, nil
	}
	return int64(n.Int16), nil
}

[ianlancetaylor]

CC @kardianos

[kardianos]

@kyleconroy This looks reasonable. Can you send a CL?

On a side note, these nullable wrappers would probably be a great use for generics...

[kyleconroy]

Yeah, can do. A bit swamped right now, but should have it done by the end of the week

[kyleconroy]

On a side note, these nullable wrappers would probably be a great use for generics...

I know! Here's a four-line replacement for the various sql.Null* types in the standard library.

    type Null(type T) struct {
        Val   T
        Valid bool // Valid is true if Val is not NULL
    }

Here's what it looks like in practice: https://go2goplay.golang.org/p/Qj8MqYWWAc3

[rsc]

Do we need NullByte for tinyint too?
(No luck for 24-bit mediumint)

[kardianos]

NullByte and NullInt16 both sound good. Might as well complete the family.

[rsc]

Based on the discussion above, this seems like a likely accept.

[rsc]

No change in consensus, so accepted.

[muhlemmer]

I have some spare time and like to contribute more to the Go project. May I volunteer for a CL @kyleconroy, or do you prefer to do it yourself?

[odeke-em]

@muhlemmer the Go tree is open for Go1.17, and it would be awesome to have you as a contributor. If you are unavailable, no biggie I’ll send one or someone from my team will send one. Thank you for the experience report @kyleconroy, and for the discussions @kardianos, @ianlancetaylor, and @rsc.

[a8m]

Hey @kyleconroy and @muhlemmer, do you have plans to submit CLs for these new types? I need them for ent and prefer to have them in the next release. Let me know if you don't have time and I can take it from here. Thanks

[odeke-em]

@alexander-melentyev sent this CL https://go-review.googlesource.com/c/go/+/305929 (thank you Alexander!) but it adds for NullUint64 which wasn’t approved, as this proposal is for NullByte and NullInt64. While it makes sense to me to also add it, we are adhering to the proposal process.

[gopherbot]

Change https://golang.org/cl/311572 mentions this issue: database/sql: add NullInt16

[gopherbot]

Change https://golang.org/cl/311989 mentions this issue: database/sql: add NullByte

[cagedmantis]

golang.org/cl/311572 is waiting for a trust +1. Is a package owner available to review?