Operator to use to compare the field to the value. The valid values are:
The operators should work similar to their corresponding SQL operators.
Complex objects can only be checked to see if they are null or not null.
"in" operator takes a list of values
"between" operator takes two values for from and thru inclusive
all others take a single value
TODO: Decide for complex Lists can they be checked to see how many occurences they have?
TODO: Decide on other operators
TODO: Deicde on operators to search collections inside such as any
TODO: Decide how to search on dynamic attributes