(Quick Reference)
                countBy*
Purpose
Dynamic method that uses the properties of the domain class to  query for the count of the number of matching records
Examples
Given the domain class 
Book:
class Book {
    String title
    Date releaseDate
    String author
}The following are all possible:
def c = Book.countByTitle("The Shining")
c = Book.countByTitleAndAuthor("The Sum of All Fears", "Tom Clancy")
c = Book.countByReleaseDateBetween(firstDate, new Date())
c = Book.countByReleaseDateGreaterThanEquals(firstDate)
c = Book.countByTitleLike("%Hobbit%")
c = Book.countByTitleNotEqual("Harry Potter")
c = Book.countByReleaseDateIsNull()
c = Book.countByReleaseDateIsNotNull()Description
GORM supports the notion of 
Dynamic Finders. The 
countBy* method counts the number of records for the given expression
The following operator names can be used within the respective dynamic methods:
- LessThan
- LessThanEquals
- GreaterThan
- GreaterThanEquals
- Between
- Like
- Ilike(i.e. ignorecase like)
- IsNotNull
- IsNull
- Not
- Equal
- NotEqual
- And
- Or
These names can be considered keywords, and you will have problems when querying domain classes that have one of these names as a property name. For more information on 
dynamic finders refer to the user guide.