Groovy Grails: Little joys

I'm working on a Groovy Grails project and I've just written a controller that takes a post from a form with only a partial representation of the object. Full representation of the object in the form is easy just do this:

  myObj.properties = params
  myObj.save()

The properties save to the Database without much fuss and if the data is invalid we'll toss back to the edit view with a bucket of error messages. But, what if I only wanted to update one field in my object from a form... or sub form... or Ajax call?

...take a look at this little slice of groovy:

public class testObj {
    Long a
    Long b
    String c
}

def t = new testObj(a:0,b:1,c:"foo");

t.properties.each({
    println it
    });

def params = ['a':1,'b':2]
println "-----------"

params.keySet().each({
    println it + "->" + params[it] 
    t[it] = params[it]
})
println "-----------"
t.properties.each({
    println it
    });

The output looks like this:

metaClass=groovy.lang.MetaClassImpl@157c2bd[class testObj]
class=class testObj
b=1
c=foo
a=0
-----------
a->1
b->2
-----------
metaClass=groovy.lang.MetaClassImpl@157c2bd[class testObj]
class=class testObj
b=2
c=foo
a=1

What just happened? We mapped the values from a Map object onto the fields of an object with out knowing what the fields in the Java object were. Without introspection.

I presume this works with a POJO and if it does I'm going to go have a party tonight because I think web form processing, ETL, and a whole mess of other ORM type activities just got a helluva lot easier in Java land.

Aren't you happy?