转载地址:http://iyiguo.net/blog/2012/09/27/mybatis-param-mapping-rules/
规则
非注解参数
当参数未使用@Param
注解时,可以通过以下方式访问:
#{参数位置[0..n-1]}
或者
#{param[1..n]}
如果参数类型是自定义对象Bean时,只需加上.对象属性
即可
#{参数位置[0..n-1].对象属性}
#{param[1..n].对象属性}
特别的,如果非注解参数只有一个时,可使用
#{任意字符}
注解参数
@Param
注释了参数后相当于给该参数指定了一个别名。注释后的参数只能通过
#{注解别名}
或者
#{param[1..n]}
如果参数类型是自定义对象Bean时,只需加上.对象属性
即可访问对象属性
#{注解别名.属性}
#{param[1..n].属性}
示例
为了明确上述规则,我们的示例具体细分了各种情况进行展示。
非注解型
一个参数
User getUserById(int id);
select * from <TABLE> where id = #{id}
// or
select * from <TABLE> where id = #{abdc}
// or
select * from <TABLE> where id = #{param1}
User getUser(User user); // user.getName user.getAge
select * from <TABLE> where name = #{name} and age = #{age}
多个参数
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}
注解型
一个参数
User getUserById(@Param(value="keyId") int id);
select * from <TABEL> where id = #{keyId}
// or
select * from <TABLE> where id = #{param1}
User getUser(@Param(value="user") 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}
多个参数
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}
非注解和注解型混合型
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.
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)
框架主要映射处理代码
参数的获取
org.apache.ibatis.binding.MapperMethod
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
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);
}
}
}
}