Mybatis SQL映射语句中参数注释规则

请查看最新整理地址：http://leeyee.github.io/blog/2012/09/27/mybatis-param-mapping-rules

 

最近在*Mybatis*的学习中对于映射语句中的参数注释设置有点犯迷糊，于是在*debug*下跟踪了下源代码，发现*Mybatis*在接口方法映射语句中会做如下处理：

1. 接口方法只有一个参数

1.1 不使用`@Param`注解

1.1.1 参数为基本类型或为基本包装类型(int,Integer,String...)

    参数注释为: #{任意字符}
   
1.1.2 参数为自定义对象

    参数注释为: #{对象属性}

示例：

    User getUserById(int id);
   
        // 注：该中情况下'任意字符'不能为空，否则报错
        // select * from <TABEL> where id = #{任意字符}
        select * from <TABLE> where id = #{id}

    User getUser(User user); // user.getName user.getAge
   
        select * from <TABLE> where name = #{name} and age = #{age}

1.2 使用`@Param`注解

1.2.1 参数为基本类型或为基本包装类型(int,Integer,String...)

    参数注释为: #{注解名称} | #{param1}
   
1.2.2 参数为自定义对象

    参数注释为: #{注解名称.对象属性} | #{param1.对象属性}
   
示例：

    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}

 
2. 接口方法有两个及两个以上参数

2.1 不使用`@Param`注解

2.1.1 参数为基本类型或为基本包装类型(int,Integer,String...)

    参数注释为: #{参数位置[0..n-1]} | #{param[1..n]}
   
2.1.2 参数为自定义对象

    参数注释为: #{参数位置[0..n-1].对象属性} | #{param[1..n].对象属性}

示例：

    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}

 

2.2 使用`@Param`注解

2.2.1 参数为基本类型或为基本包装类型(int,Integer,String...)

    参数注释为: #{注解名称} | #{param[1..n]}
   
2.2.2 参数为自定义对象

    参数注释为: #{注解名称.对象属性} | #{param[1..n].对象属性}

示例：

    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}

 
2.2.3 部分参数使用`@Param`注解

当采用部分参数使用`@Param`注解时，参数注释为将以上两种情况结合起来即可。

示例：

 

User getUser(String name, @Param(value="nl") age, int gendar);

// 对于age的访问不能是 #{1} 只能是 #{param2} | #{nl}
select * from <TABLE> where name = #{0} and age = #{nl} and gendar = #{param3)

 

 

总结下

• `@Param`的作用是设置参数别名。设置后的参数只能通过`#{param[1..n]`或者`#{注解别名}`来访问

• 多个参数情况下，均可使用  `#{参数位置[0..n-1]}` |   `#{param[1..n]}`来访问参数

最后给出几个源代码中关于参数设置的源代码供大家参考：

 

参数获取操作：org.apache.ibatis.binding.MapperMethod.getParam(Object[] args)

    private Object getParam(Object[] args) {
        final int paramCount = paramPositions.size();
        // 无参数
        if (args == null || paramCount == 0) {
            return null;
        // 无注解并参数个数为1
        } else if (!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
        // 这就是 #{param[1..n]} 的来源
        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;
        }
    }

SQL预编译参数设置：org.apache.ibatis.executor.parameter.DefaultParameterHandler.setParameters(PreparedStatement ps) throws SQLException  

org.apache.ibatis.executor.parameter.DefaultParameterHandler.setParameters(PreparedStatement ps) throws SQLException

    public void 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;
                    } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
                        value = parameterObject;
                    } else if (boundSql.hasAdditionalParameter(propertyName)) {
                        value = boundSql.getAdditionalParameter(propertyName);
                    } else if (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) {
                    throw new 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);
                }
            }
        }
    }