spanner: provide column types in results

[rakyll]

The underlying proto contains ResultSetMetadata.RowType for results returned from the API but spanner.Row or spanner.RowIterator are not surfacing them to the user. I'm trying to put together a "database/sql" driver for Spanner and without the column type it is not possible.

/cc @tbpg

[rakyll]

spanner.GenericColumnValue seems to be doing what I want to do.

[hengfengli]

Hi @rakyll, I think currently, using spanner.GenericColumnValue is right choice when you don't know in advance what column type to expect.

In client library, we have the type info in Row.fields[i].Type, which returns *sppb.Type (sppb "google.golang.org/genproto/googleapis/spanner/v1"). However, the type info is not exposed. If we want to expose this info, we might need to add the following code in line 167 of row.go after ColumnNames() method:

// ColumnRawTypes returns all column raw types of the row.
func (r *Row) ColumnRawTypes() []*sppb.Type {
	var n []string
	for _, c := range r.fields {
		n = append(n, c.Type)
	}
	return n
}

[hengfengli]

Hi @rakyll , do you think whether or not the proposed method is a solution for your problem? or have you already solved your problem?

Is this still a feature that you would like us to add?

[rakyll]

spanner.GenericColumnValue worked for my case. I can close this issue, thanks.

[apstndb]

I want to see ResultSetMetadata.RowType even when there are empty results.
It is available using raw API and gcloud but unavailable using spanner.GenericColumnValue because there is no Row.

$ gcloud spanner databases execute-sql ${DATABASE_ID} --sql='SELECT * FROM (SELECT 1) LIMIT 0' --format=yaml
metadata:
  rowType:
    fields:
    - type:
        code: INT64
  transaction: {}

I believe it is useful to write a generic client application.

[olavloite]

It does seem that the Go client does not return the metadata of a result set, which makes it impossible to determine the column names and types of an empty result set.