class Book {
   String title
   Date releaseDate
   String author
   static constraints = {
      releaseDate nullable: true
   }
}findOrCreateWhere
Purpose
Uses named arguments that match the property names of the domain class to produce a query that returns the first result.  This method behaves just like findWhere except that it will never return null.  If a matching instance cannot be found then a new instance will be created, populated with values from the query parameters and returned.  The difference between this method and findOrSaveWhere is that this method will not save a newly created instance where findOrSaveWhere does.
Examples
Given the domain class:
You can query in the form:
def book = Book.findOrCreateWhere(author: "Stephen King", title: "The Stand")Description
Parameters:
- 
queryParams- AMapof key/value pairs to be used in the query. If no matching instance is found then this data is used to initialize a new instance.