implement count operation

src/main/java/casser/core/CasserEntityCache.java

@@ -24,7 +24,7 @@ public class CasserEntityCache {
 
 	private ConcurrentMap<Class<?>, CasserMappingEntity<?>> cache = new ConcurrentHashMap<Class<?>, CasserMappingEntity<?>>();
 
-	public CasserMappingEntity<?> getEntity(Class<?> iface) {
+	public CasserMappingEntity<?> getOrCreateEntity(Class<?> iface) {
 		
 		CasserMappingEntity<?> entity = cache.get(iface);
 		

src/main/java/casser/core/CasserSession.java

@@ -21,6 +21,7 @@ import java.util.Set;
 
 import casser.core.dsl.Getter;
 import casser.core.dsl.Setter;
+import casser.core.operation.CountOperation;
 import casser.core.operation.DeleteOperation;
 import casser.core.operation.SelectOperation;
 import casser.core.operation.UpdateOperation;
@@ -167,6 +168,16 @@ public class CasserSession extends AbstractSessionOperations implements Closeabl
 				p1, p2, p3, p4, p5, p6, p7);
 	}
 	
+	public CountOperation count(Object dsl) {
+		Objects.requireNonNull(dsl, "dsl is empty");
+		
+		Class<?> iface = MappingUtil.getMappingInterface(dsl);
+		
+		CasserMappingEntity<?> entity = entityCache.getOrCreateEntity(iface);
+		
+		return new CountOperation(this, entity);
+	}
+	
 	public <V> UpdateOperation update(Setter<V> setter, V v) {
 		Objects.requireNonNull(setter, "field is empty");
 		Objects.requireNonNull(v, "value is empty");
@@ -181,7 +192,7 @@ public class CasserSession extends AbstractSessionOperations implements Closeabl
 		
 		Class<?> iface = MappingUtil.getMappingInterface(pojo);
 		
-		CasserMappingEntity<?> entity = entityCache.getEntity(iface);
+		CasserMappingEntity<?> entity = entityCache.getOrCreateEntity(iface);
 		
 		return new UpsertOperation(this, entity, pojo);
 	}
@@ -191,7 +202,7 @@ public class CasserSession extends AbstractSessionOperations implements Closeabl
 		
 		Class<?> iface = MappingUtil.getMappingInterface(dsl);
 		
-		CasserMappingEntity<?> entity = entityCache.getEntity(iface);
+		CasserMappingEntity<?> entity = entityCache.getOrCreateEntity(iface);
 		
 		return new DeleteOperation(this, entity);
 	}

src/main/java/casser/core/SessionInitializer.java

@@ -115,7 +115,7 @@ public class SessionInitializer extends AbstractSessionOperations {
 		
 		Class<?> iface = MappingUtil.getMappingInterface(dsl);
 		
-		CasserMappingEntity<?> entity = entityCache.getEntity(iface);
+		CasserMappingEntity<?> entity = entityCache.getOrCreateEntity(iface);
 		
 		if (type == AutoDsl.CREATE || type == AutoDsl.CREATE_DROP) {
 			createNewTable(entity);

src/main/java/casser/core/operation/CountOperation.java

@@ -16,19 +16,40 @@
 package casser.core.operation;
 
 import casser.core.AbstractSessionOperations;
+import casser.core.Filter;
+import casser.mapping.CasserMappingEntity;
 
 import com.datastax.driver.core.ResultSet;
 import com.datastax.driver.core.querybuilder.BuiltStatement;
+import com.datastax.driver.core.querybuilder.QueryBuilder;
+import com.datastax.driver.core.querybuilder.Select;
+import com.datastax.driver.core.querybuilder.Select.Where;
 
-public class CountOperation extends AbstractObjectOperation<Long, CountOperation> {
+public class CountOperation extends AbstractFilterOperation<Long, CountOperation> {
 
-	public CountOperation(AbstractSessionOperations sessionOperations) {
+	private final CasserMappingEntity<?> entity;
+	
+	public CountOperation(AbstractSessionOperations sessionOperations, CasserMappingEntity<?> entity) {
 		super(sessionOperations);
+		
+		this.entity = entity;
 	}
 
 	@Override
 	public BuiltStatement buildStatement() {
-		return null;
+		
+		Select select = QueryBuilder.select().countAll().from(entity.getTableName());
+		
+		if (filters != null && !filters.isEmpty()) {
+		
+			Where where = select.where();
+			
+			for (Filter<?> filter : filters) {
+				where.and(filter.getClause());
+			}
+		}
+		
+		return select;
 	}
 	
 	@Override

src/main/java/casser/core/operation/SelectOperation.java

@@ -49,7 +49,23 @@ public class SelectOperation<E> extends AbstractFilterStreamOperation<E, SelectO
 	}
 	
 	public CountOperation count() {
-		return null;
+		
+		CasserMappingEntity<?> entity = null;
+		for (CasserMappingProperty<?> prop : props) {
+			
+			if (entity == null) {
+				entity = prop.getEntity();
+			}
+			else if (entity != prop.getEntity()) {
+				throw new CasserMappingException("you can count records only from a single entity " + entity.getMappingInterface() + " or " + prop.getEntity().getMappingInterface());
+			}
+		}
+		
+		if (entity == null) {
+			throw new CasserMappingException("no entity or table to count data");
+		}
+		
+		return new CountOperation(sessionOperations, entity);
 	}
 	
 	public <R> SelectOperation<R> map(Function<E, R> fn) {

src/test/java/casser/test/integration/core/simple/SimpleUserTest.java

@@ -51,6 +51,9 @@ public class SimpleUserTest extends AbstractEmbeddedCassandraTest {
 		session.update(user::setName, "albert").set(user::setAge, 35)
 			.where(user::getId, "==", 123L).sync();
 		
+		long cnt = session.count(user).where(user::getId, "==", 123L).sync();
+		Assert.assertEquals(1L, cnt);
+
 		String name = session.select(user::getName)
 				.where(user::getId, "==", 123L)
 				.sync()