groovy sql eachRow and rows method

Question

I am new to grails and groovy. Can anyone please explain to me the difference between these two groovy sql methods

sql.eachRow
sql.rows

Also, w

Answer 1

If we set aside minor syntax differences, there is one difference that seems important. Let's consider

sql.rows("select * from my_table").each { row -> doIt(row) }

vs

sql.eachRow("select * from my_table") { row -> doIt(row) }

The first one opens connection, retrieves results, closes connection and returns them. Now you can iterate over the results while connection is released. The drawback is you now have entire result list in memory which in some cases might be a lot.

EachRow on the other hand opens a connection and while keeping it open executes your closure for each row. If your closure operates on the database and requires another connection your code will consume two connections from the pool at the same time. The connection used by eachRow is released after it iterates though all the resulting rows. Also if you don't perform any database operations but closure takes a while to execute, you will be blocking one database connection until eachRow completes.

I am not 100% sure but possibly eachRow allows you not to keep all resulting rows in memory but access them through a cursor - this may depend on the database driver.

If you don't perform any database operations inside your closure, closure executes fast and results list is big enough to impact memory then I'd go for eachRow. If you do perform DB operations inside closure or each closure call takes significant time while results list is manageable, then go for rows.