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LimitOffsetQueryRewriter.java
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LimitOffsetQueryRewriter.java
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/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* 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, 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 org.apache.metamodel.jdbc.dialects;
import org.apache.metamodel.jdbc.JdbcDataContext;
import org.apache.metamodel.query.Query;
/**
* Query rewriter for databases that support LIMIT and OFFSET keywords for max
* rows and first row properties.
*/
public abstract class LimitOffsetQueryRewriter extends DefaultQueryRewriter {
public LimitOffsetQueryRewriter(JdbcDataContext dataContext) {
super(dataContext);
}
@Override
public final boolean isFirstRowSupported(final Query query) {
return true;
}
@Override
public final boolean isMaxRowsSupported() {
return true;
}
/**
* {@inheritDoc}
*
* If the Max rows and/or First row property of the query is set, then we
* will use the database's LIMIT and OFFSET functions.
*/
@Override
public String rewriteQuery(Query query) {
String queryString = super.rewriteQuery(query);
Integer maxRows = query.getMaxRows();
Integer firstRow = query.getFirstRow();
if (maxRows != null || firstRow != null) {
if (maxRows == null) {
maxRows = Integer.MAX_VALUE;
}
queryString = queryString + " LIMIT " + maxRows;
if (firstRow != null && firstRow > 1) {
// offset is 0-based
int offset = firstRow - 1;
queryString = queryString + " OFFSET " + offset;
}
}
return queryString;
}
}