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grailsgroovy

I'm getting a NullPointerException when accessing static constraints

The code

${personRequest.constraints.requestStatus.inList}

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

Solution

  • 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.