title: grails - strange behaviour after data binding
body: <p>it is very common to use domainClass.properties = params to bind all incoming request params to a domain class object. i do not understand why this assignment automatically updates the domain object. e.g.</p>
  
  <pre><code>def update = {
    def book = Book.get(1)
    book.properties = params
    book.discard()
  }
  </code></pre>
  
  <p>the params assignment updates the domain object. discard method has no effect. can anyone help me?</p>