View Javadoc

1   /*
2    * Copyright 2006-2012 the original author or authors.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package org.springframework.batch.item.database.support;
18  
19  import org.springframework.util.StringUtils;
20  
21  /**
22   * Postgres implementation of a  {@link org.springframework.batch.item.database.PagingQueryProvider} using database specific features.
23   * 
24   * When using the groupClause, this implementation expects all select fields not used in aggregate functions to be included in the 
25   * groupClause (the provider does not add them for you).
26   *
27   * @author Thomas Risberg
28   * @author Michael Minella
29   * @since 2.0
30   */
31  public class PostgresPagingQueryProvider extends AbstractSqlPagingQueryProvider {
32  
33  	@Override
34  	public String generateFirstPageQuery(int pageSize) {
35  		return SqlPagingQueryUtils.generateLimitSqlQuery(this, false, buildLimitClause(pageSize));
36  	}
37  
38  	@Override
39  	public String generateRemainingPagesQuery(int pageSize) {
40  		if(StringUtils.hasText(getGroupClause())) {
41  			return SqlPagingQueryUtils.generateLimitGroupedSqlQuery(this, true, buildLimitClause(pageSize));
42  		}
43  		else {
44  			return SqlPagingQueryUtils.generateLimitSqlQuery(this, true, buildLimitClause(pageSize));
45  		}
46  	}
47  
48  	private String buildLimitClause(int pageSize) {
49  		return new StringBuilder().append("LIMIT ").append(pageSize).toString();
50  	}
51  	
52  	@Override
53  	public String generateJumpToItemQuery(int itemIndex, int pageSize) {
54  		int page = itemIndex / pageSize;
55  		int offset = (page * pageSize) - 1;
56  		offset = offset<0 ? 0 : offset;
57  		String limitClause = new StringBuilder().append("LIMIT 1 OFFSET ").append(offset).toString();
58  		return SqlPagingQueryUtils.generateLimitJumpToQuery(this, limitClause);
59  	}
60  
61  }