adds implementation of driver.RowsNextResultSet interface

[basvanbeek]

Go's database/sql package supports multiple resultsets.

To enable this feature the driver.RowsNextResultSet interface must be implemented by the database driver. This PR adds the implementation for this.

[abradley201]

Hi basvanbeek,

If you haven't done so already, please review the CLA on this page:
https://github.com/VoltDB/voltdb-client-go/blob/master/CONTRIBUTING.md

Before we merge any commits, all contributors must sign and submit the CLA form to support@voltdb.com. Thank you.

[basvanbeek]

Hi @abradley201, already signed and returned the CLA some time ago. If you look at the repo stats you'll notice there is already contributed code of mine merged previously.

[abradley201]

Thank you. We will review the code for merging soon.
-Andrew

[benjaminballard]

Hi Bas, yes, we're all set on your CLA. We have it on file.

[basvanbeek]

@benjaminballard @abradley201 is there something I can do to expedite this?

[basvanbeek]

@benjaminballard friendly ping... I'd rather use the official package instead of a fork but need this for our production code.

[benjaminballard]

I've asked someone in Engineering to look at this today.

[QingyangWtg]

Can you explain why you need to change the return type to pointer here?
If so, function return types also need update.

[basvanbeek]

Because I needed to add func (vr *VoltRows) NextResultSet() error which needs to change the current table index. Function return type does not need an update as it is an interface itself.

[QingyangWtg]

I see. But I assume the the query result would be stored to some local variable before issue the NextResultSet() method, right? So that nextResultSet still be able to call upon that variable? i.e

rows, err := conn.Query(....)
for rows.HasNextResultSet() {
      .....
      rows.NextResultSet()  // x.m() is shorthand for (&x).m() ? https://golang.org/ref/spec#Calls
}

[basvanbeek]

So yes Go has automatic dereferencing of pointers but that's not the issue here.

The problem is that because we must update vr.tableIndex I must use a pointer receiver in the NextResultSet method (func (vr *VoltRows) NextResultSet()). If purely working on the VoltRows object itself this is no issue. However VoltRows needs to implement driver.RowsNextResultSet as this is the enhancement interface sql/database tests against for
this logic. Here lies the problem, if providing the composite literal VoltRows{} instead of a pointer to it &VoltRows{}; it will not satisfy the interface and sql/database will assume the driver does not support multiple result sets and NextResultSet will always return false.

I've added a unit test so this can easily be demonstrated as well as a compile time assertion for the driver.RowsNextResultSet interface. Remove the & and see stuff fail.

[QingyangWtg]

I see, that make sense. Thanks for the detailed explanation.