org.apache.cassandra.distributed.api.QueryResult Maven / Gradle / Ivy
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* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.cassandra.distributed.api;
import java.util.Iterator;
import java.util.List;
import java.util.function.Function;
import java.util.function.Predicate;
/**
* A table of data representing a complete query result.
*
* A QueryResult is different from {@link java.sql.ResultSet} in several key ways:
*
*
* - represents a complete result rather than a cursor
* - returns a {@link Row} to access the current row of data
* - relies on object pooling; {@link #hasNext()} may return the same object just with different data, accessing a
* {@link Row} from a previous {@link #hasNext()} call has undefined behavior.
* - includes {@link #filter(Predicate)}, this will do client side filtering since Apache Cassandra is more
* restrictive on server side filtering
*
*
* Unsafe patterns
*
* Below are a few unsafe patterns which may lead to unexpected results
*
* {@code
* while (rs.hasNext()) {
* list.add(rs.next());
* }
* }
*
* {@code
* rs.forEach(list::add)
* }
*
* Both cases have the same issue; reference to a row from a previous call to {@link #hasNext()}. Since the same {@link Row}
* object can be used across different calls to {@link #hasNext()} this would mean any attempt to access after the fact
* points to newer data. If this behavior is not desirable and access is needed between calls, then {@link Row#copy()}
* should be used; this will clone the {@link Row} and return a new object pointing to the same data.
*/
public interface QueryResult extends Iterator
{
List names();
List warnings();
default QueryResult filter(Predicate fn)
{
return QueryResults.filter(this, fn);
}
default Iterator map(Function fn)
{
return new Iterator()
{
@Override
public boolean hasNext()
{
return QueryResult.this.hasNext();
}
@Override
public A next()
{
return fn.apply(QueryResult.this.next());
}
};
}
}