How can I debug NPE in Grails? - grails

Question

I try to execute raw SQL in Grails with this code:
class PlainSqlService {
def dataSource // the Spring-Bean "dataSource" is auto-injected
def newNum = {
def sql = new Sql(dataSource) // Create a new instance of groovy.sql.Sql with the DB of the Grails app
def q = "SELECT a.xaction_id, a.xdin FROM actions a WHERE a.is_approved = 0"
def result = sql.rows(q) // Perform the query
return result
}
}
But I get this exception at runtime.
sql object is not null!
How can I debug it?
2011-02-13 15:55:27,507 [http-8080-1] ERROR errors.GrailsExceptionResolver - Exception occurred when processing request: [GET] /moderator/login/index
Stacktrace follows:
java.lang.NullPointerException
at moderator.PlainSqlService$_closure1.doCall(PlainSqlService.groovy:17)
at moderator.PlainSqlService$_closure1.doCall(PlainSqlService.groovy)
at moderator.LoginController$_closure1.doCall(LoginController.groovy:29)
at moderator.LoginController$_closure1.doCall(LoginController.groovy)
at java.lang.Thread.run(Thread.java:662)

Answer 1

It's hard to tell what's going on from the limited code you're providing, but there are some things to check. Is the service injected into the controller with a class-scope field "def plainSqlService" like you have here for the dataSource, or are you calling new PlainSqlService()? If you're creating a new instance then the dataSource bean won't be injected and the groovy.sql.Sql constructor won't fail, but queries will.
One thing to try is grails clean - whenever something like this that should work doesn't, a full recompile often helps.
One important but unrelated point - you should never use Closures in services. Controllers and taglibs require that actions and tags be implemented with a Closure, but a Service is just a Spring bean defined in Groovy. Spring knows nothing about Closures and since they're just a field that Groovy executes as if it were a method, any proxying that you're expecting from Spring (in particular transactional behavior, but also security and other features) will not happen since Spring only looks for methods.
So newNum should be declared as:
def newNum() {
...
}