[R-sig-DB] DBI package

[Paul Gilbert]

On 13-10-17 11:02 PM, Hadley Wickham wrote:
>> I think Seth's proposal would mean that users would need to change the
>> TSconnect calls to something like
>>    con1 <- TSconnect(MySQL(), dbname="test")
>>    con2 <- TSconnect(SQLite(), dbname="test")
>>
>> I don't object to making changes if they fix a problem, but I don't think
>> this actually fixes the problem that I pointed out. The user session still
>> needs to find the function MySQL() or SQLite(), which means my package need
>> to indicate RMySQL or RSQLite as Depends rather than Imports.
>
> Well, the problem is that relying on strings to identify database
> drivers is not in general a good approach.

Agreed, just pointing out that it does not fix the problem I mentioned, 
which I think was the starting point for that thread.

>For your code, you could do
> something like:
>
> find_driver <- function(name) {
>    getExportedValue(paste0("R", name), name)()
> }
>
> setMethod("TSconnect",   signature(drv="character", dbname="character"),
>     definition=function(drv, dbname, ...)
>               TSconnect(find_driver(drv), dbname=dbname, ...))
>
> It may be worthwhile to include find_driver in DBI.

Thanks for the suggestion, however, I remain a bit confused. The 
function find_driver() seems like a direct replacement for dbConnect(), 
using a string to identify the database driver. You would be supporting 
what is a bad idea, and just changing the name of the function, which is 
a make work project for everyone.

If you do put it in DBI you probably want a try() wrapper so that it 
fails gracefully when the appropriate package is not attached.

Paul

>
> Hadley
>
>