Ibatis之3個不常用的Query方法

來源：懂視網責編：小采時間：2020-11-09 14:36:36

Ibatis之3個不常用的Query方法

Ibatis之3個不常用的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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導讀Ibatis之3個不常用的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;

當查詢對象是一個重量級對象、創(chuàng)建過程比較復雜時或者查詢對象沒有默認的構造方法時，通過該方法，可以在外部先構建好查詢對象，然后傳給Ibatis，Ibatis此時不會創(chuàng)建新對象，而是調用傳入對象的set方法進行賦值。

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;

利用這個方法可以實現分頁功能，如（skip=0,max=10）返回前10條數據，(skip=10,max=10)返回第10-20條數據，但這個方法的分頁效率非常低，因為Ibatis是把所有的查詢結果查詢出來之后才進行篩選操作。數據量小的時候用用還可以，所以這個方法比較雞肋。

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;

網上有不少帖子說這個方法只能返回一條記錄是不對的，還有說是把resultClass的所有屬性放到一個map中返回來也是不對的。這個方法是對queryForList的一個補充，大部分情況下我們用的都是queryForList返回對象的列表，但有時候放到Map里用起來可能更方便，如果沒有這個方法還得自己進行轉換，同樣的一個