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/*
* Copyright 2006-2012 Amazon Technologies, Inc. or its affiliates.
* Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
* of Amazon Technologies, Inc. or its affiliates. All rights reserved.
*
* Licensed 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,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.amazon.carbonado.qe;
import java.io.IOException;
import com.amazon.carbonado.Cursor;
import com.amazon.carbonado.FetchException;
import com.amazon.carbonado.Query;
import com.amazon.carbonado.Storable;
import com.amazon.carbonado.cursor.LimitCursor;
import com.amazon.carbonado.cursor.SkipCursor;
import com.amazon.carbonado.filter.FilterValues;
/**
* AbstractQueryExecutor implements a small set of common QueryExecutor methods.
*
* @author Brian S O'Neill
*/
public abstract class AbstractQueryExecutor<S extends Storable> implements QueryExecutor<S> {
public Class<S> getStorableType() {
return getFilter().getStorableType();
}
/**
* Produces a slice via skip and limit cursors. Subclasses are encouraged
* to override with a more efficient implementation.
*
* @since 1.2
*/
public Cursor<S> fetchSlice(FilterValues<S> values, long from, Long to) throws FetchException {
Cursor<S> cursor = fetch(values);
if (from > 0) {
cursor = new SkipCursor<S>(cursor, from);
}
if (to != null) {
cursor = new LimitCursor<S>(cursor, to - from);
}
return cursor;
}
/**
* Produces a slice via skip and limit cursors. Subclasses are encouraged
* to override with a more efficient implementation.
*
* @since 1.2
*/
public Cursor<S> fetchSlice(FilterValues<S> values, long from, Long to,
Query.Controller controller)
throws FetchException
{
Cursor<S> cursor = fetch(values, controller);
if (from > 0) {
cursor = new SkipCursor<S>(cursor, from);
}
if (to != null) {
cursor = new LimitCursor<S>(cursor, to - from);
}
return cursor;
}
/**
* Counts results by opening a cursor and skipping entries. Subclasses are
* encouraged to override with a more efficient implementation.
*/
public long count(FilterValues<S> values) throws FetchException {
Cursor<S> cursor = fetch(values);
try {
long count = cursor.skipNext(Integer.MAX_VALUE);
if (count == Integer.MAX_VALUE) {
int amt;
while ((amt = cursor.skipNext(Integer.MAX_VALUE)) > 0) {
count += amt;
}
}
return count;
} finally {
cursor.close();
}
}
/**
* Counts results by opening a cursor and skipping entries. Subclasses are
* encouraged to override with a more efficient implementation.
*/
public long count(FilterValues<S> values, Query.Controller controller) throws FetchException {
Cursor<S> cursor = fetch(values, controller);
try {
long count = cursor.skipNext(Integer.MAX_VALUE);
if (count == Integer.MAX_VALUE) {
int amt;
while ((amt = cursor.skipNext(Integer.MAX_VALUE)) > 0) {
count += amt;
}
}
return count;
} finally {
cursor.close();
}
}
/**
* Does nothing and returns false.
*/
public boolean printNative(Appendable app, int indentLevel, FilterValues<S> values)
throws IOException
{
return false;
}
/**
* Appends spaces to the given appendable. Useful for implementing
* printNative and printPlan.
*/
protected void indent(Appendable app, int indentLevel) throws IOException {
for (int i=0; i<indentLevel; i++) {
app.append(' ');
}
}
/**
* Appends a newline character.
*/
protected void newline(Appendable app) throws IOException {
app.append('\n');
}
/**
* Adds a constant amount to the given indent level. Useful for
* implementing printNative and printPlan.
*/
protected int increaseIndent(int indentLevel) {
return indentLevel + 2;
}
}
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