In Domain class with manyToOne relations the autocomplete seems to be a bit random, suggests methods that should not be available and do not suggest methods that should be there.  

To recreate
Create 2 domain classes:

class Book {
    String name
    Author author
    static belongsTo = [autor: Author]
}

class Author {
    String name
    List books
    static hasMany = [books: Book]
}

Author a = new Author()

a.books.
or
a.getBooks().

Here one would expect methods from Groovy List Object
http://groovy.codehaus.org/groovy-jdk/java/util/List.html

as well as DefaultGroovyMethods


Possible overlap with bug: https://netbeans.org/bugzilla/show_bug.cgi?id=234248