Adding a new DBI backend

First steps

For interactive exploation, attach dplyr and DBI. If you’re creating a package, you’ll need to import dplyr and DBI.

library(dplyr)
library(DBI)

Check that you can create a tbl from a connection, like:

con <- DBI::dbConnect(RSQLite::SQLite(), path = ":memory:")
DBI::dbWriteTable(con, "mtcars", mtcars)
#> [1] TRUE

tbl(con, "mtcars")
#> # Source:   table<mtcars> [?? x 11]
#> # Database: sqlite 3.11.1 []
#>     mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb
#>   <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1  21.0     6   160   110  3.90  2.62  16.5     0     1     4     4
#> 2  21.0     6   160   110  3.90  2.88  17.0     0     1     4     4
#> 3  22.8     4   108    93  3.85  2.32  18.6     1     1     4     1
#> 4  21.4     6   258   110  3.08  3.21  19.4     1     0     3     1
#> # ... with more rows

If you can’t, this likely indicates some problem with the DBI methods. Use DBItest to narrow down the problem.

Now is a good time to implement a method for db_desc(). This should briefly describe the connection, typically formatting the information returned form dbGetInfo(). This is what dbplyr does for Postgres connections:

#' @export
db_desc.PostgreSQLConnection <- function(x) {
  info <- dbGetInfo(x)
  host <- if (info$host == "") "localhost" else info$host

  paste0("postgres ", info$serverVersion, " [", info$user, "@",
    host, ":", info$port, "/", info$dbname, "]")
}

Coping, computing, collecting and collapsing

Next, check that copy_to(), collapse(), compute(), and collect() work.

• If copy_to() fails, it’s likely you need a method for db_write_table(), db_create_indexes() or db_analyze().

• If collapse() fails, your database has a non-standard way of constructing subqueries. Add a method for sql_subquery().

• If compute() fails, your database has a non-standard way of saving queries in temporary tables. Add a method for db_save_query().

SQL translation

Make sure you’ve read vignette("sql-translation") so you have the lay of the land.