Lists of raw vectors should map to blobs by default

[krlmlr]

RPostgres, RMySQL and RSQLite map those to BLOBs. However, DBI doesn't declare the dbDataType method for lists, and the BLOB data type doesn't seem to be part of SQL-92.

Shall we add

setMethod("dbiDataType", "list", function(x) "blob")

to DBI?

CC @hannesmuehleisen.

[hannes]

fine with me.

[hadley]

How would lists get serialised into the database? I think this is part of a broader issue of allowing people to register custom serialisers and deserialisers for non-standard SQL types/R classes.

[krlmlr]

Lists (with raw vectors inside) already seem to be serialized as BLOBs in the existing rstats-db backends, but I don't have a test for that yet.

[hadley]

On option would be to do something like this:

setMethod("dbiDataType", "list", function(x) {
  is_raw <- vapply(x, is.raw, logical(1))
  if (all(is_raw)) {
    return("blob")
  }

  stop("Only lists of raw vectors are currently support", call. = FALSE)
})

[krlmlr]

A thin S3 wrapper is another option:

as.raw_list <- function(x) {
  check_raw_list(x)
  structure(x, class = "raw_list")
}

Here, the checking needs to be done only once during construction.