Numeric to float64 conversion doesn't work

[crodwell]

The built in method AssignTo() for converting a postgresql numeric such as Numeric(5,2) to float64 does not work.

[crodwell]

could be fixed with following code

func (src *Numeric) Float64() float64 {
    f, err := strconv.ParseFloat(src.Int.String(), 64)
    if err != nil {
        return 0
    }
    var roundTo float64 = 1
    if src.Exp > 0 {
        for i := 0; i < int(src.Exp); i++ {
            f *= 10
            roundTo *= 10
        }
    } else if src.Exp < 0 {
        for i := 0; i > int(src.Exp); i-- {
            f /= 10
            roundTo /= 10
        }
    }
    return math.Round(f/roundTo) * roundTo
}

[jackc]

As far as it not working, do you have an example?

There is a passing test for assigning to float:

pgtype/numeric_test.go

Line 255 in ab5e597

{src: &pgtype.Numeric{Int: big.NewInt(42), Exp: -1, Status: pgtype.Present}, dst: &f64, expected: float64(4.2)},

[crodwell]

Hi Jack,

Sorry for being vague, it's an accuracy issue, so if I have 10.06 in my database:

		var test float64
		err = myFiveTwoNumeric.AssignTo(&test)
		fmt.Println(test)
		fmt.Println(myFiveTwoNumeric.Float64())

output:
10.059999999999999
10.06

Also the AssignTo method returning an error isn't as easy to use as when the dev just wants a float representation of the Big.Int, the same way I can get a .String or .Int from varchar/int4 types.

[jackc]

Should be fixed now.

As far as convenience goes AssignTo is mostly used internally. If you need a float64 you can scan directly into that and skip the numeric step. A public Float64() method would need an error return as well to handle null and undefined states.

Beyond that, pgtype.Numeric provides just enough functionality to transcode numeric values. https://github.com/shopspring/decimal provides a real decimal type in Go. pgtype.Numeric doesn't use it to avoid forcing an external dependency on everyone. But if you are using numerics you can use https://github.com/jackc/pgtype/tree/master/ext/shopspring-numeric to integrate with a real decimal type.