Ibatis之3个不常用的Query方法

来源：懂视网责编：小采时间：2020-11-09 14:36:36

Ibatis之3个不常用的Query方法

Ibatis之3个不常用的Query方法:1.queryForObject /** * Executes a mapped SQL SELECT statement that returns data to populate * the supplied result object. * p/ * The parameter object is generally used to supply the input * data for the WHERE clause parameter(s) of the SEL

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导读Ibatis之3个不常用的Query方法:1.queryForObject /** * Executes a mapped SQL SELECT statement that returns data to populate * the supplied result object. * p/ * The parameter object is generally used to supply the input * data for the WHERE clause parameter(s) of the SEL

1.queryForObject /** * Executes a mapped SQL SELECT statement that returns data to populate * the supplied result object. * p/ * The parameter object is generally used to supply the input * data for the WHERE clause parameter(s) of the SEL

1.queryForObject

 /**
 * Executes a mapped SQL SELECT statement that returns data to populate
 * the supplied result object.
 * 
 * The parameter object is generally used to supply the input
 * data for the WHERE clause parameter(s) of the SELECT statement.
 *
 * @param id The name of the statement to execute.
 * @param parameterObject The parameter object (e.g. JavaBean, Map, XML etc.).
 * @param resultObject The result object instance that should be populated with result data.
 * @return The single result object as supplied by the resultObject parameter, populated with the result set data,
 * or null if no result was found
 * @throws java.sql.SQLException If more than one result was found, or if any other error occurs.
 */
 Object queryForObject(String id, Object parameterObject, Object resultObject) throws SQLException;

当查询对象是一个重量级对象、创建过程比较复杂时或者查询对象没有默认的构造方法时，通过该方法，可以在外部先构建好查询对象，然后传给Ibatis，Ibatis此时不会创建新对象，而是调用传入对象的set方法进行赋值。

2.queryForList

 /**
 * Executes a mapped SQL SELECT statement that returns data to populate
 * a number of result objects within a certain range.
 * 
 * This overload assumes no parameter is needed.
 *
 * @param id The name of the statement to execute.
 * @param skip The number of results to ignore.
 * @param max The maximum number of results to return.
 * @return A List of result objects.
 * @throws java.sql.SQLException If an error occurs.
 */
 List queryForList(String id, int skip, int max) throws SQLException;

利用这个方法可以实现分页功能，如（skip=0,max=10）返回前10条数据，(skip=10,max=10)返回第10-20条数据，但这个方法的分页效率非常低，因为Ibatis是把所有的查询结果查询出来之后才进行筛选操作。数据量小的时候用用还可以，所以这个方法比较鸡肋。

3.queryForMap

/**
 * Executes a mapped SQL SELECT statement that returns data to populate
 * a number of result objects that will be keyed into a Map.
 * 
 * The parameter object is generally used to supply the input
 * data for the WHERE clause parameter(s) of the SELECT statement.
 *
 * @param id The name of the statement to execute.
 * @param parameterObject The parameter object (e.g. JavaBean, Map, XML etc.).
 * @param keyProp The property to be used as the key in the Map.
 * @return A Map keyed by keyProp with values being the result object instance.
 * @throws java.sql.SQLException If an error occurs.
 */
 Map queryForMap(String id, Object parameterObject, String keyProp) throws SQLException;

网上有不少帖子说这个方法只能返回一条记录是不对的，还有说是把resultClass的所有属性放到一个map中返回来也是不对的。这个方法是对queryForList的一个补充，大部分情况下我们用的都是queryForList返回对象的列表，但有时候放到Map里用起来可能更方便，如果没有这个方法还得自己进行转换，同样的一个