ways to get the max&min value of a Freeze map index?

[peterlspot]

Dear pals,

Just wonder if there r any C++ API to retrieve the current maximum and minimum values of a particular index field in a freeze map?

Suppose there is students map based on the following SLICE:

class Student
{
int id;
string name;
}

and the corresponding freeze map is indexed on the field "id".

Is there any ways to find out the current min & max values of the "id" field stored in the student map.

Thanks

[matthew]

Indexed fields will generate additional methods. From the Ice manual:

iterator findByMEMBER(MEMBER_TYPE, bool = true); 
const_iterator findByMEMBER(MEMBER_TYPE, bool = true) const; 
iterator lowerBoundForMEMBER(MEMBER_TYPE); 
const_iterator lowerBoundForMEMBER(MEMBER_TYPE) const; 
iterator upperBoundForMEMBER(MEMBER_TYPE); 
const_iterator upperBoundForMEMBER(MEMBER_TYPE) const; 
std::pair<iterator, iterator> 
equalRangeForMEMBER(MEMBER_TYPE); 
std::pair<const_iterator, const_iterator> 
equalRangeForMEMBER(MEMBER_TYPE) const; 
int MEMBERCount(MEMBER_TYPE) const;

You should also check issue 11 of our newsletter connections which has an article on these methods.

Following, assuming that you also set the sort function to less<int> then to find the lowest id you could do:

m.lowerBoundForId(0);

which will return an iterator to either the record with id 0, or the first record after this. In either case, assuming you never store records with an id < 0 then you are all set

Unfortunately, computing the biggest id is more difficult. You might think you could use upperBoundForId:

m.upperBoundForId(MAX_INT);

However, since you cannot iterate backwards with a freeze map iterator (they are not bidirectional iterators) then this return value does you no good.

Some alternate solutions to help:
- You could create another id field id2 that contains an identical id, index upon that and sort in the opposite direction (greater<int>). Then lowerBoundForId2(MAX_INT) would find the biggest id.
- You could create a dummy record and sort the biggest id in that field and use lowerBoundForId to find the lowest.
- You could compute the biggest and smallest on startup and cache them during the application run.

All things being equal likely the last is the simplest solution.