how to return the sum of a value in a table with where clause in grails 2.5.0 - sql

Question

Domain class:
class Transaction {
String roundId
BigDecimal amount
:
}
The SQL we wish to execute the following:
"select sum(t.amount) from transaction t where t.roundId = xxx"
We have been unable to find an example which does not return Transaction rows.
We assume there are two approaches:
Use projections and/or criteria etc? All the examples we have found only return lists of transaction rows, not the sum.
Use raw SQL. How do we call SQL, and get a handle on the BigDecimal it returns?
I tried this:
class bla{
def sessionFactory
def someMethod() {
def SQLsession = sessionFactory.getCurrentSession()
def results = SQLsession.createSQLQuery("select sum(t.credit) from transaction t where t.round_id = :roundId", [roundId: roundId])
But this fails with
groovy.lang.MissingMethodException: No signature of method: org.hibernate.internal.SessionImpl.createSQLQuery() is applicable for argument types: (java.lang.String, java.util.LinkedHashMap)
Also, I have no idea what the return type would be (cant find any documentation). I am guessing it will be a list of something: Arrays? Maps?
==== UPDATE ====
Found one way which works (not very elegant or grails like)
def SQLsession = sessionFactory.getCurrentSession()
final query = "select sum(t.credit) from transaction t where t.round_id = :roundId"
final sqlQuery = SQLsession.createSQLQuery(query)
final results = sqlQuery.with {
setString('roundId', roundId)
list() // what is this for? Is there a better return value?
}
This seems to return an array, not a list as expected, so I can do this:
if (results?.size == 1) {
println results[0] // outputs a big decimal
}
Strangely, results.length fails, but results.size works.

Answer 1

Using Criteria, you can do
Transaction.withCriteria {
eq 'roundId', yourRoundIdValueHere
projections {
sum 'amount'
}
}

Answer 2

https://docs.jboss.org/hibernate/core/3.3/api/org/hibernate/classic/Session.html
Query createSQLQuery(String sql, String[] returnAliases, Class[] returnClasses)
Query createSQLQuery(String sql, String returnAlias, Class returnClass)
The second argument of createSQLQuery is one or more returnAliases and not meant for binding the statement to a value.
Instead of passing your values in the 2nd argument, use the setters of your Query object i.e. setString, setInteger, etc.
results.setInteger('roundId',roundId);