Self-contained SQL transactions

Description

Given that transactions are implemented, this function allows you to pass in code that is run in a transaction. The default method of dbWithTransaction calls dbBegin before executing the code, and dbCommit after successful completion, or dbRollback in case of an error. The advantage is that you don't have to remember to do dbBegin and dbCommit or dbRollback – that is all taken care of. The special function dbBreak allows an early exit with rollback, it can be called only inside dbWithTransaction.

Usage

dbWithTransaction(conn, code)

dbBreak()

Arguments

Value

The result of the evaluation of code

Side Effects

The transaction in code on the connection conn is committed or rolled back. The code chunk may also modify the local R environment.

Examples

con <- dbConnect(RSQLite::SQLite(), ":memory:")

dbWriteTable(con, "cars", head(cars, 3))
dbReadTable(con, "cars")   # there are 3 rows

## successful transaction
dbWithTransaction(con, {
  dbExecute(con, "INSERT INTO cars (speed, dist) VALUES (1, 1);")
  dbExecute(con, "INSERT INTO cars (speed, dist) VALUES (2, 2);")
  dbExecute(con, "INSERT INTO cars (speed, dist) VALUES (3, 3);")
})
dbReadTable(con, "cars")   # there are now 6 rows

## failed transaction -- note the missing comma
tryCatch(
  dbWithTransaction(con, {
    dbExecute(con, "INSERT INTO cars (speed, dist) VALUES (1, 1);")
    dbExecute(con, "INSERT INTO cars (speed dist) VALUES (2, 2);")
    dbExecute(con, "INSERT INTO cars (speed, dist) VALUES (3, 3);")
  }),
  error = identity
)
dbReadTable(con, "cars")   # still 6 rows

## early exit, silently
dbWithTransaction(con, {
  dbExecute(con, "INSERT INTO cars (speed, dist) VALUES (1, 1);")
  dbExecute(con, "INSERT INTO cars (speed, dist) VALUES (2, 2);")
  if (nrow(dbReadTable(con, "cars")) > 7) dbBreak()
  dbExecute(con, "INSERT INTO cars (speed, dist) VALUES (3, 3);")
})
dbReadTable(con, "cars")   # still 6 rows

dbDisconnect(con)