tree 10c25de8d479ea4c2d7da3a0264d35465fd34230
parent be07a624a2e4501df135ab7f731b7cfb408d9df2
author Jean de Klerk <deklerk@google.com> 1571863036 -0600
committer Knut Olav Løite <koloite@gmail.com> 1575882065 +0000

spanner: Allow decoding Spanner values to custom types.

This change adds support for decoding result set values from Spanner
into custom types that point back to supported types. This allows
decoding a result set into for example a struct like this:

type blobField []byte
type dbProductInfo struct {
    ProductID  int64     `spanner:"ProductID"`
    UpdateDate time.Time `spanner:"UpdateDate"`
    Data       blobField `spanner:"Data"`
}

Decoding Spanner column values to one of the known types
(string, []byte, int64, float64, time.Timestamp, civil.Date) and
their known Null<type> versions is done using a type switch
statement. Decoding to a custom type is done with reflection. The
reason for not using reflection for all types, including the known
base types, is the performance difference. Benchmark results executed
locally showing the difference between the two are shown below based
on decoding a single string value to a standard string or a custom
string type.

goos: linux
goarch: amd64
pkg: cloud.google.com/go/spanner
BenchmarkDecodeString-8         200000000   8.21 ns/op
BenchmarkDecodeCustomString-8   10000000    135  ns/op

Updates #1610.
Fixes #853.

Change-Id: Iad689b3704acadb83809375c762a7e0b564a7b2f
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/48090
Reviewed-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Tyler Bui-Palsulich <tbp@google.com>
Reviewed-by: Hengfeng Li <hengfeng@google.com>