Mybatis SQL對映語句中引數註解使用規則
來源:http://blog.csdn.net/oxcow/article/details/8024717/
最近在*Mybatis*的學習中對於對映語句中的引數註釋設定有點犯迷糊,於是在*debug*下跟蹤了下原始碼,發現*Mybatis*在介面方法對映語句中會做如下處理:
1. 介面方法只有一個引數
1.1 不使用`@Param`註解
1.1.1 引數為基本型別或為基本包裝型別(int,Integer,String...)
引數註釋為: #{任意字元}
1.1.2 引數為自定義物件
引數註釋為: #{物件屬性}
示例:
-
<span mce_style="font-size: medium;"
- // 注:該中情況下'任意字元'不能為空,否則報錯
- // select * from <TABEL> where id = #{任意字元}
- select * from <TABLE> where id = #{id}
- User getUser(User user); // user.getName user.getAge
-
select * from <TABLE> where name = #{name} and age = #{age}</span>
1.2 使用`@Param`註解
1.2.1 引數為基本型別或為基本包裝型別(int,Integer,String...)
引數註釋為: #{註解名稱} | #{param1}
1.2.2 引數為自定義物件
引數註釋為: #{註解名稱.物件屬性} | #{param1.物件屬性}
示例:
- <span mce_style="font-size: medium;" style="font-size:14px; "> User getUserById(@Param(value="keyId") int id);
-
select * from <TABEL> where id = #{keyId}
- // or
- select * from <TABLE> where id = #{param1}
- User getUser(@Param(value="usr") User user); // user.getName user.getAge
- select * from <TABLE> where name = #{user.name} and age = #{user.age}
- // or
- select * from <TABLE> where name = #{param1.name} and age = #{param1.age}</span>
2. 介面方法有兩個及兩個以上引數
2.1 不使用`@Param`註解
2.1.1 引數為基本型別或為基本包裝型別(int,Integer,String...)
引數註釋為: #{引數位置[0..n-1]} | #{param[1..n]}
2.1.2 引數為自定義物件
引數註釋為: #{引數位置[0..n-1].物件屬性} | #{param[1..n].物件屬性}
示例:
- <span mce_style="font-size: medium;" style="font-size:14px; "> User getUser(String name, int age);
- select * from <TABLE> where name = #{0} and age = #{1}
- // or
- select * from <TABLE> where name = #{param1} and age = #{param2}
- User getUser(User usr, int flag);
- select * from <TABLE> where name = #{0.name} and age = {0.age} and flag = #{1}
- // or
- select * from <TABLE> where name = #{param1.name} and age = {param1.age} and flag = #{param2}</span>
2.2 使用`@Param`註解
2.2.1 引數為基本型別或為基本包裝型別(int,Integer,String...)
引數註釋為: #{註解名稱} | #{param[1..n]}
2.2.2 引數為自定義物件
引數註釋為: #{註解名稱.物件屬性} | #{param[1..n].物件屬性}
示例:
- <span mce_style="font-size: medium;" style="font-size:14px; "> User getUser(@Param(value="xm") String name, @Param(value="nl") int age);
- select * from <TABLE> where name = #{xm} and age = #{nl}
- // or
- select * from <TABLE> where name = #{param1} and age = #{param2}
- // or
- select * from <TABLE> where name = #{xm} and age = #{param2}
- User getUser(@Param(value="usr") User user, @Param(value="tag") int flag);
- select * from <TABLE> where name = #{usr.name} and age = #{usr.age} and flag = #{tag}
- // or
- select * from <TABLE> where name = #{param1.name} and age = #{param1.age} and flag = #{param2}
- // or
- select * from <TABLE> where name = #{usr.name} and age = #{param1.age} and flag = #{param2}</span>
2.2.3 部分引數使用`@Param`註解
當採用部分引數使用`@Param`註解時,引數註釋為將以上兩種情況結合起來即可。
示例:
- <span mce_style="font-size: medium;" style="font-size:14px; ">User getUser(String name, @Param(value="nl") age, int gendar);
- // 對於age的訪問不能是 #{1} 只能是 #{param2} | #{nl}
- select * from <TABLE> where name = #{0} and age = #{nl} and gendar = #{param3)</span>
總結下
- `@Param`的作用是設定引數別名。設定後的引數只能通過`#{param[1..n]`或者`#{註解別名}`來訪問
- 多個引數情況下,均可使用 `#{引數位置[0..n-1]}` | `#{param[1..n]}`來訪問引數
最後給出幾個原始碼中關於引數設定的原始碼供大家參考:
引數獲取操作:org.apache.ibatis.binding.MapperMethod.getParam(Object[] args)
- <span mce_style="font-size: medium;" style="font-size:14px; "> private Object getParam(Object[] args) {
- finalint paramCount = paramPositions.size();
- // 無引數
- if (args == null || paramCount == 0) {
- returnnull;
- // 無註解並引數個數為1
- } elseif (!hasNamedParameters && paramCount == 1) {
- return args[paramPositions.get(0)];
- } else {
- Map<String, Object> param = new MapperParamMap<Object>();
- for (int i = 0; i < paramCount; i++) {
- param.put(paramNames.get(i), args[paramPositions.get(i)]);
- }
- // issue #71, add param names as param1, param2...but ensure backward compatibility
- // 這就是 #{param[1..n]} 的來源
- for (int i = 0; i < paramCount; i++) {
- String genericParamName = "param" + String.valueOf(i + 1);
- if (!param.containsKey(genericParamName)) {
- param.put(genericParamName, args[paramPositions.get(i)]);
- }
- }
- return param;
- }
- }</span>
SQL預編譯引數設定:org.apache.ibatis.executor.parameter.DefaultParameterHandler.setParameters(PreparedStatement ps) throws SQLException
- <span mce_style="font-size: medium;" style="font-size:14px; ">org.apache.ibatis.executor.parameter.DefaultParameterHandler.setParameters(PreparedStatement ps) throws SQLException
- publicvoid setParameters(PreparedStatement ps)
- throws SQLException {
- ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
- List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
- if (parameterMappings != null) {
- MetaObject metaObject = parameterObject == null ? null : configuration.newMetaObject(parameterObject);
- for (int i = 0; i < parameterMappings.size(); i++) {
- ParameterMapping parameterMapping = parameterMappings.get(i);
- if (parameterMapping.getMode() != ParameterMode.OUT) {
- Object value;
- String propertyName = parameterMapping.getProperty();
- PropertyTokenizer prop = new PropertyTokenizer(propertyName);
- if (parameterObject == null) {
- value = null;
- } elseif (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
- value = parameterObject;
- } elseif (boundSql.hasAdditionalParameter(propertyName)) {
- value = boundSql.getAdditionalParameter(propertyName);
- } elseif (propertyName.startsWith(ForEachSqlNode.ITEM_PREFIX)
- && boundSql.hasAdditionalParameter(prop.getName())) {
- value = boundSql.getAdditionalParameter(prop.getName());
- if (value != null) {
- value = configuration.newMetaObject(value).getValue(propertyName.substring(prop.getName().length()));
- }
- } else {
- value = metaObject == null ? null : metaObject.getValue(propertyName);
- }
- TypeHandler typeHandler = parameterMapping.getTypeHandler();
- if (typeHandler == null) {
- thrownew ExecutorException("There was no TypeHandler found for parameter " + propertyName + " of statement " + mappedStatement.getId());
- }
- JdbcType jdbcType = parameterMapping.getJdbcType();
- if (value == null && jdbcType == null) jdbcType = configuration.getJdbcTypeForNull();
- typeHandler.setParameter(ps, i + 1, value, jdbcType);
- }
- }
- }
- }</span>