Java 用于检索多行的 JDBCTemplate queryForMap
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JDBCTemplate queryForMap for retrieving multiple rows
提问by user182944
Can I use queryForMapif there are multiple rows returned by the query.
queryForMap如果查询返回多行，我可以使用吗？
For a single row, the below code works fine.
对于单行，下面的代码工作正常。
public Map<String, Object> retrieveMultipleRowsColumns(String deptName){
return jdbcTemplate.queryForMap("SELECT DEPT_ID,DEPT_NAME FROM DEPT WHERE DEPT_NAME = ?", deptName);
}
How to modify this for multiple rows?
如何为多行修改这个？
采纳答案by John Farrelly
Use queryForListsee the javadoc for full details. It returns List<Map<String,Object>>
queryForList有关完整的详细信息，请参阅 javadoc。它返回List<Map<String,Object>>
public List<Map<String, Object>> retrieveMultipleRowsColumns(String deptName){
return jdbcTemplate.queryForList("SELECT DEPT_ID,DEPT_NAME FROM DEPT WHERE DEPT_NAME = ?", deptName);
}
回答by suresh chaudhari
public <T> List<T> queryForList(String sql,
Class<T> elementType,
Object... args)
throws DataAccessException
Description copied from interface: JdbcOperations Query given SQL to create a prepared statement from SQL and a list of arguments to bind to the query, expecting a result list. The results will be mapped to a List (one entry for each row) of result objects, each of them matching the specified element type.
从接口复制的描述：JdbcOperations 查询给定 SQL 以从 SQL 创建准备好的语句和绑定到查询的参数列表，期望结果列表。结果将映射到结果对象的列表（每行一个条目），每个对象都匹配指定的元素类型。
Specified by:queryForListin interface JdbcOperations ,
Parameters:sql- SQL query to execute elementType - the required type of element in the result list (for example, Integer.class)args- arguments to bind to the query (leaving it to the PreparedStatement to guess the corresponding SQL type); may also contain SqlParameterValueobjects which indicate not only the argument value but also the SQL type and optionally the scale Returns:a List of objects that match the specified element type Throws: DataAccessException - if the query failsSee Also:JdbcOperations.queryForList(String, Class), SingleColumnRowMapper
指定者：queryForList在接口 JdbcOperations 中，
Parameters:sql- 执行的 SQL 查询 elementType - 结果列表中所需元素的类型（例如，Integer.class）args- 绑定到查询的参数（将其留给 PreparedStatement 以猜测相应的 SQL 类型); 也可以contain SqlParameterValue对象不仅指示参数值，还指示 SQL 类型和可选的比例返回：匹配指定元素类型的对象列表抛出：DataAccessException - 如果查询失败另见：JdbcOperations.queryForList(String, Class),单列行映射器
回答by Brian Beech
I know this is really old, but there is a much simpler way to do this if you're looking for a map.
我知道这真的很旧，但是如果您正在寻找地图，有一种更简单的方法可以做到这一点。
Simply implement the ResultSetExtractor interface to define what type you want to return. Below is an example of how to use this. You'll be mapping it manually, but for a simple map, it should be straightforward.
只需实现 ResultSetExtractor 接口即可定义要返回的类型。下面是一个如何使用它的例子。您将手动映射它，但对于简单的地图，它应该很简单。
jdbcTemplate.query("select string1,string2 from table where x=1", new ResultSetExtractor<Map>(){
@Override
public Map extractData(ResultSet rs) throws SQLException,DataAccessException {
HashMap<String,String> mapRet= new HashMap<String,String>();
while(rs.next()){
mapRet.put(rs.getString("string1"),rs.getString("string2"));
}
return mapRet;
}
});
This will give you a return type of Map that has multiple rows (however many your query returned) and not a list of Maps. You can view the ResultSetExtractor docs here: http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/jdbc/core/ResultSetExtractor.html
这将为您提供具有多行（无论您返回多少查询）的 Map 返回类型，而不是 Maps 列表。您可以在此处查看 ResultSetExtractor 文档：http: //docs.spring.io/spring/docs/current/javadoc-api/org/springframework/jdbc/core/ResultSetExtractor.html
