How to get DB connection in grails 3 - grails

Question

What is proper way to get DB connection in Grails 3?
For grails 2 following code has works:
((SessionImpl) sessionFactory.getCurrentSession()).connection() // sessionFactory initialized in bootstrap
But after migration to Grails 3 sometimes I see exceptions in the log:
java.sql.SQLException: Operation not allowed after ResultSet closed at
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:957) at
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:896) at
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:885) at
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860) at
com.mysql.jdbc.ResultSetImpl.checkClosed(ResultSetImpl.java:743) at
com.mysql.jdbc.ResultSetImpl.findColumn(ResultSetImpl.java:1037) at
com.mysql.jdbc.ResultSetImpl.getLong(ResultSetImpl.java:2757) at
com.mchange.v2.c3p0.impl.NewProxyResultSet.getLong(NewProxyResultSet.java:424)
at java_sql_ResultSet$getLong$3.call(Unknown Source)
It happens for 0,01% of requests
Grails 3.2.11
Gorm 6.0.12

Answer 1

I guess it depends on where you need it, but you can inject a DataSource into a service.
javax.sql.DataSource dataSource
Then you can just use
dataSource.getConnection()
Also be aware of the changes to flush mode in GORM 6 (http://gorm.grails.org/6.0.x/hibernate/manual/ section 1.2.1). If an upstream save/commit is failing, your result set could be incidentally closed and trigger an error that looks like this while not really have anything to do with this particular line of code at all. I'd (very temporarily) set back to the old flush mode and see if the problem goes away, before tracking much more down!

Answer 2

From grails docs, you can get the actual dataSource bean. From that you can access the connection or use it to query your db
import groovy.sql.Sql
def dataSource
println "connection: ${dataSource.connection}"
Sql sql = new Sql(dataSource)
sql.eachRow("SELECT * FROM note") { row ->
println "row: ${row}"
}
Use 'dataSourceUnproxied' to avoid Hibernate transaction and session issues:
def dataSourceUnproxied

Answer 3

For executing queries inside current hibernate transactions following construction can be used:
sessionFactory.currentSession.doWork {connection ->
new Sql(connection).execute(query, params)
}