1 Overview
First of all, it is clear that this annotation is for parameter assignment in the SQL statement.
The role of @Param is to name the parameters, such as a method A (int id) in the mapper, when an annotation is added, A (@Param("userId") int id), which means that the external wants to retrieve the passed id value , Just take its parameter name userId. Pass the parameter value as in the SQL statement, and assign the value to the SQL parameter through #{userId}.
2. Examples:
Example 1: @Param annotates basic types of parameters
Methods in mapper:
public User selectUser(@Param("userName") String name,@Param("password") String pwd);Map to the <select> tag in xml
<select id="selectUser" resultMap="User">
select * from user where user_name = #{userName} and user_password=#{password}
</select>Where user_name = #{userName} and user_password = #{password} the userName and password are all taken from the annotation @Param(), and the values taken out are the values of the formal parameters String name and String pwd in the method.
Example 2: @Param annotation JavaBean object
The SQL statement uses the alias in the @Param annotation to take out the attributes in the object and copy it
Methods in mapper:
public List<User> getAllUser(@Param("user") User u);Map to the <select> tag in xml
<select id="getAllUser" parameterType="com.vo.User" resultMap="userMapper">
select
from user t where 1=1
and t.user_name = #{user.userName}
and t.user_age = #{user.userAge}
</select> 3, notes
When the @Param annotation is used to declare parameters, the value of the SQL statement uses #{}, and the value of ${} can be used.
When you do not use the @Param annotation to declare parameters, you must use #{} to take the parameters. If you use ${} to get a value, an error will be reported.
When the @Param annotation is not used, there can be only one parameter, and it is a Javabean. JavaBean properties can be referenced in SQL statements, and only JavaBean properties can be referenced.
@Select("SELECT * from Table where id = ${id}")
Enchashment selectUserById(User user);