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, which is more efficient?

I am working on an application that retrieves data from the database(the resultset is very huge) and writes it to CSV file or returns a JSON format.

I was wondering which of the two methods mentioned above to use to have the process done faster and efficient.

Answer 1

Can anyone please explain to me the difference between these two groovy sql methods sql.eachRow sql.rows

It's difficult to tell exactly which 2 methods you're referring 2 because there are a large number of overloaded versions of each method. However, in all cases, eachRow returns nothing

void eachRow(String sql, Closure closure)

whereas rows returns a list of rows

List rows(String sql) 

So if you use eachRow, the closure passed in as the second parameter should handle each row, e.g.

sql.eachRow("select * from PERSON where lastname = 'murphy'") { row ->
    println "$row.firstname"
}

whereas if you use rows the rows are returned, and therefore should be handled by the caller, e.g.

rows("select * from PERSON where lastname = 'murphy'").each {row ->
    println "$row.firstname"        
}

Also, which is more efficient?

This question is almost unanswerable. Even if I had implemented these methods myself there's no way of knowing which one will perform better for you because I don't know

• what hardware you're using
• what JVM you're targeting
• what version of Groovy you're using
• what parameters you'll be passing
• whether this method is a bottleneck for your application's performance

or any of the other factors that influence a method's performance that cannot be determined from the source code alone. The only way you can get a useful answer to the question of which method is more efficient for you is by measuring the performance of each.

Despite everything I've said above, I would be amazed if the performance difference between these two was in any way significant, so if I were you, I would choose whichever one you find more convenient. If you find later on that this method is a performance bottleneck, try using the other one instead (but I'll bet you a dollar to a dime it makes no difference).

Answer 2

They differ in signature only - both support result sets paging, so both will be efficient. Use whichever fits your code.