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Querying in Collections and Arrays

Hazelcast enables querying in collections and arrays.

Let's have a look at the following data structure:

class Swap {
   Leg legs[2];
}

class Leg {
   String currency;
}

In order to query a single element of a collection/array, you can execute the following query:

IMap<Integer, Swaps> swap = getMap();
// this matches all swaps where the 1st leg's currency is 'EUR'
Predicate p = Predicates.equals('legs[0].currency', 'EUR');
Collection<Swap> result = map.values(p);

It is also possible to query a collection/array usint the any semantics as shown below:

IMap<Integer, Swaps> swap = getMap();
// this matches all swaps where any leg's currency is 'EUR'
Predicate p = Predicates.equals('legs[any].currency', 'EUR');
Collection<Swap> result = map.values(p);

The exact same query may be executed using the SQLPredicate as shown below:

Predicate p = new SQLPredicate('legs[any].currency = EUR');
Collection<Swap> result = map.values(p);

[] notation applies to both collections and arrays.

Indexing in Collections and Arrays

You can also create indexes in collections/arrays. Note that the attribute used in the index definition has to be the same as the one used in the query.

Let's assume you have the following index definition:

<indexes>
  <index ordered="false">leg[any].currency</index>
</indexes>

The following predicate will use the index:

Predicate p = Predicates.equals('leg[any].currency', 'EUR');

The following predicate, however, will NOT use the index:

Predicates.equals('leg[0].currency', 'EUR')

In order to use the index in the above mentioned case, you would have to create another index as shown below:

<indexes>
  <index ordered="false">leg[0].currency</index>
</indexes>