Support nil pointers to value implementing driver.Valuer

[kdar]

For example, you can't do something like this:

var d *apd.Decimal
fmt.Println(pool.Exec(`INSERT INTO test (value) VALUES ($1)`, d))

Relevant discussion with the Go stdlib is here: golang/go#8415
Commit fixing this in Go stdlib is here: golang/go@0ce1d79

[kdar]

I'm also not sure if pgx checks properly if a type implements driver.Valuer with a pointer receiver. When I try, I get an error like this:

cannot convert {0xc4201e2120} to Numeric

Instead of calling Value() on the pointer receiver, it seems to try to coerce the pointer into Numeric.

[jackc]

I used the same fix as was done for the standard lib. It now incurs a reflect operation for each driver.Valuer argument, but there doesn't seem to be any way around it.

[kdar]

Do you have any insight into the second comment I made on this issue?

Just to clarify what I'm doing, is I'm trying to avoid having to create a wrapper type to check if it's null.

type Decimal struct {...}

func (z *Decimal) Value() (driver.Value, error) {
  if z == nil {
    return nil, nil
  }
  return z.String(), nil
}

Let me know if this endeavor is inane and I should just use a NullDecimal wrapper type.

[jackc]

I don't think you should need a wrapper. I have a working test in the test suite with a nil *apd.Decimal so you should be able to do the same that it does.