Should dbDataType dispatch to the default AsIs method in custom backends?

[MichaelChirico]

I have a custom backend where we need a custom method for dbDataType() for logical() ("BOOL" instead of "SMALLINT").

https://cloud.google.com/bigquery/docs/reference/standard-sql/data-types

I'd rather back up to the default dispatch where possible, so instead of writing out a full custom R type->backend type mapping, I've just added one method for logical():

setMethod(
  "dbDataType", c("MyDBIConnection", "logical"),
  \(dbObj, obj, ...) "BOOL"
)

However, that fails the {DBItest} suite:

`expect_identical(...)` threw an unexpected error. ('test-DBITest.R:54:1')
--------------------------------------------------------------------------------
`expect_identical(...)` threw an unexpected error.
Message: dbDataType(dbObj, I(FALSE)) (`actual`) not identical to dbDataType(dbObj, FALSE) (`expected`).

`actual`:   "SMALLINT"
`expected`: "BOOL"    
Class:   expectation_failure/expectation/error/condition

My S4 knowledge is pretty weak, but IIUC the issue is that AsIs does not dispatch to the correct method:

DBI/R/dbiDataType_AsIs.R

Lines 1 to 6 in 9d28b2a

	dbiDataType_AsIs <- function(x) {
	oldClass(x) <- oldClass(x)[-1]
	dbiDataType(x)
	}
	setMethod("dbiDataType", signature("AsIs"), dbiDataType_AsIs)

So I had to wind up just copy-pasting that as a new c("MyDBIConnection", "AsIs") method.

But shouldn't that be the default behavior so I don't need to copy over boilerplate? That would just mean adding a specific c("DBIConnection", "AsIs") method, right?

(happy to file a PR, but checking my understanding first)

[krlmlr]

Thanks. There is a nasty message that can't be turned off when more than one S4 method matches. Copying the boilerplate is the easiest way to shut off that message.

I'm not sure if this applies here, so worth a check.

[MichaelChirico]

I'll investigate when I get to a suitable machine for doing so :)