HazelcastQueryAPI Predicates Sınıfı - Predicate API

Nasıl Çalışır

Açıklaması şöyle. Yani Predicate tüm üyelere gönderilir, sonuçları ise istekte bulunan istemci birleştirir

The requested predicate is sent to each member in the cluster. Each member looks at its own local entries and filters them according to the predicate. At this stage, key/value pairs of the entries are deserialized and then passed to the predicate. The predicate requester merges all the results coming from each member into a single set.

Sonuçları QueryableEntry#extractAttributeValue() metodu alır. 

Eğer aranılan attribute string "list[0].attribute1" gibi karmaşık bir şeyse Extractors sınıfı ile getter bulunur. 

Extractor sınıfı ReflectionHelper sınıfını kullanarak belirtilen attribute string'ini "." karakterine göre ayırır ve en alttaki getter metodu bulur

Nasıl Kullanılır

Predicate nesneleri şu metodlar ile kullanılır

IMap.entrySet(Predicate)

IMap.values(Predicate)

equals metodu

com.hazelcast.query.impl.predicates.EqualPredicate döndürür

Örnek

Şöyle yaparız

class TestData implements Serializable {

  private static final long serialVersionUID = 1L;

  private String attr1;
  private String attr2;
  ... 
}

IMap<String, TestData> map = instance1.getMap(...);
map.executeOnEntries(new TestLoggingEntryProcessor(), Predicates.equal("attr1", "foo"));

Örnek - JSON

Şöyle yaparız

Collection<HazelcastJsonValue> departmentWithMatchSalary = departments.values(
  Predicates.equal("people[any].salary", 50000));

in metodu

com.hazelcast.query.impl.predicates.InPredicate döndürür

Örnek

Şöyle yaparız

IMap<String, String> map = ...

// Add some entries to the map
map.put("key1", "value1");
map.put("key2", "value2");
map.put("key3", "value3");

// Create a predicate to search for entries with specific keys
Predicate<String, String> keyPredicate = Predicates.in("key1", "key2");

// Get the entries from the map that match the predicate
Collection<String> values = map.values(keyPredicate);

sql metodu

SQL'in çoğu şeyi destekleniyor

Predicates.sql() metodu veya new SqlPredicate() nesnesi kullanılabilir. SqlPredicate Sınıfını kullacaksak  şu satırı dahil ederiz

import com.hazelcast.query.impl.predicates.SqlPredicate;

Örnek - Field Value

Şöyle yaparız

IMap<Integer, Employee> employees = ...;

Predicate sqlPredicate = new SqlPredicate(
  String.format("lastName = '%s'",emp.getLastName()));

Collection<Employee> matching = employees.values(sqlPredicate);

// wildcards are supported, too - look for last names starting
// with 'D' using the same 'values' call.
sqlPredicate = new SqlPredicate("lastName like 'D%'");
matching = employees.values(sqlPredicate);

// compound predicates work, as well
sqlPredicate = new SqlPredicate("lastName like 'D%' and age between 21 and 30");
matching = employees.values(sqlPredicate);

// this could go on, but it's a pretty robust subset of sql functionality.
sqlPredicate = new SqlPredicate("deptId not in (13, 23, 33)");
matching = employees.values(sqlPredicate);

Örnek - Enum Value

Elimizde şöyle bir kod olsun

public enum MyState {
  STATE1 {
    @Override
    public boolean isTest() { return false; }
  },
  STATE2 {
    @Override
    public boolean isTest() { return true; }
  };

  public abstract boolean isTest();
}

public static class MyEmployee implements Serializable {
   MyState state;

   public MyEmployee(MyState state) {
     this.state = state;
   }

   @Override
   public boolean equals(Object o) {
     if (this == o) return true;
     if (o == null || getClass() != o.getClass()) return false;
     MyEmployee that = (MyEmployee) o;
     return state == that.state;
   }

   @Override
   public int hashCode() {
     return Objects.hash(state);
   }
}

Şöyle yaparız

HazelcastInstance instance = ...;
IMap<Integer, MyEmployee> map = instance.getMap("map");

MyEmployee employee1 = new MyEmployee(State.STATE1);
map.put(1, employee1);


MyEmployee employee2 = new MyEmployee(State.STATE2);
map.put(2, employee2);


Collection<MyEmployee> values = map.values(Predicates.sql("state.test = true"));
assertThat(values).containsExactly(employee2);

Örnek

Şöyle yaparız

import com.hazelcast.query.Predicates;

IMap<String, Employee> map = instance.getMap("employees");
map.addIndex(IndexType.SORTED, "age");
map.addIndex(IndexType.HASH, "active");

Set<Map.Entry<String, Employee>> entries = map
  .entrySet(Predicates.sql("active=true and age>44"));