Documentation: if DBI::dbConnect() is the way to connect dplyr to DBs then should require initExtension()

[JohnMount]

If DBI::dbConnect() is now the preferred way to connect dplyr to DBs then the documentation should include how to trigger initExtension() (or the equivalent) for each common database. For example this is functionality that is in dplyr::src_sqlite(), but not triggered when using DBI::dbConnect() directly on a SQLite database. This means switching the connection method can break downstream code.

Example:

suppressPackageStartupMessages(library("dplyr"))
packageVersion("dplyr")
#> [1] '0.7.4'

d <- data.frame(x = 1:2)
small <- 1

# SQLite example

#my_db <- dplyr::src_sqlite(":memory:", create = TRUE)
my_db <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")
#RSQLite::initExtension(my_db) # needed for many summary fns.

dSQLite <- copy_to(my_db, d, 'dSQLite')

dSQLite %>% 
  mutate(z = STDEV(x))
#> Error in rsqlite_send_query(conn@ptr, statement): no such function: STDEV

[hadley]

I think we should just handle this in RSQLite: r-dbi/RSQLite#236