Clean way to wrap-up and handle RMySQL connections? - r

Question

I'm fairly new to R, so forgive me if this is a amateur question. I still don't get parts of how the R language works and I haven't used closures enough to really build intuition on how to approach this problem.
I want to wrap up opening and closing a database connection in my R project in a clean way. I have a variety of scripts set aside that all use a common DB connection configuration file (I don't put it in my repo, it's a local file only), all of which need to connect to the same MySQL database.
The end goal is to do something like :
query <- db_open()
out <- query("select * from example limit 10")
db_close()
This is what I wrote so far (all my scripts load these functions from another .R file) :
db_open <- function() {
db_close()
db_conn <<- dbConnect(MySQL(), user = db_user, password = db_pass, host = db_host)
query <- function(...) { dbGetQuery(db_conn, ...) }
return(query)
}
db_close <- function() {
result <- tryCatch({
dbDisconnect(db_conn)
}, warning = function(w) {
# ignore
}, error = function(e) {
return(FALSE)
})
return(result)
}
I'm probably thinking of this in an OOP way when I shouldn't be, but sticking db_conn in the global environment feels unnecessary or even wrong.
Is this a reasonable way to accomplish what I want? Is there a better way that I'm missing here?
Any advice is appreciated.

Answer 1

You basically had it, you just need to move the query function into its own function. Regarding keeping db_conn, there really is no reason not to have it in the global environment.
db_open <- function() {
db_close()
db_conn <<- dbConnect(MySQL(), user='root', password='Use14Characters!', dbname='msdb_complex', host='localhost')
}
db_close <- function() {
result <- tryCatch({
dbDisconnect(db_conn)
}, warning = function(w) {
# ignore
}, error = function(e) {
return(FALSE)
})
return(return)
}
query <- function(x,num=-1)
{
q <- dbSendQuery(db_conn, x)
s <- fetch(q, num);
}
Then you should be able to do something like:
query <- db_open()
results <- query("SELECT * FROM msenrollmentlog", 10)
db_close()