Question

The code

${personRequest.constraints.requestStatus.inList} 

in my gsp file throws a NullPointerException, but new PersonRequest().constraints.. works. Why? Isn’t constraints static?

Answer 1

Copied from here (grails-user mailing list)

but why accesing to static fields doesnt work?

Because the ‘constraints’ static field is a closure property. It has no sub-properties relating to the constraints.

Grails evaluates this closure using a constraint builder which monitors ‘calls’ to methods that don’t exist, i.e. the property names you use:

type( inList: [xxxxx]) 

…causes a method call to ‘type’ with a Map parameter containing ‘inList’ ==> some value.

From this info, Grails builds up a list of all the constraints
available and binds them to future instances of the domain class.

So, when you access User.constraints statically, you are getting a
Closure.

We -could- look at replacing the value of the static constraints property at runtime after evaluating the Closure it is initialized with. However this could be a bit ‘too much’ magic. What do people think?

FYI it’s like this now because until 0.4 (if I recall) constraints weren’t static, and in 0.4 they can still be non-static. Only in 0.5
will we throw an exception/ignore non-static constraints.