MyBatis annotations in @Param four usage scenarios, the last one often overlooked!

There are some small partners feel that when there are multiple parameters MyBatis only method You need to add @Param notes, in fact, this understanding is not accurate. Even MyBatis a single parameter, it may also be used @Param comment.

However, before you summed up the law, you may feel strange, sometimes an argument obviously do not add @Param notes, sometimes, they need to add, do not add error.

Some people will think this is a pot of various versions of the difference of MyBatis, undeniable, MyBatis has developed rapidly, the differences between the different versions quite obvious, but this did to @Param annotated problem, but not the version of pot ! Today, Song Ge and everyone to chat on this issue, in the end under what circumstances need to add @Param comment.

First, we need to add the following few notes @Param scene, I believe we all have a consensus:

The first: a plurality of method parameters, annotation requires @Param

Such as the following:

@Mapper
public interface UserMapper {
    Integer insert(@Param("username") String username, @Param("address") String address);
}
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Corresponding XML file as follows:

<insert id="insert" parameterType="org.javaboy.helloboot.bean.User">
    insert into user (username,address) values (#{username},#{address});
</insert>
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This is the most common @Param need to add annotations scene.

The second: To alias method parameters, need @Param comment

When it is desired to an alias of the parameters, we also need @Param annotation, such a method is defined as follows:

@Mapper
public interface UserMapper {
    User getUserByUsername(@Param("name") String username);
}
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Corresponding XML is defined as follows:

<select id="getUserByUsername" parameterType="org.javaboy.helloboot.bean.User">
    select * from user where username=#{name};
</select>
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Honestly, not much of this demand, trouble.

Third: XML in SQL using the $, the argument also needs @Param comment

$There will be problems injection vulnerability, but sometimes you have to use$ Symbols, such as the name of the column to pass table name or when, this time must be added @Param notes, for example:

@Mapper
public interface UserMapper {
    List<User> getAllUsers(@Param("order_by")String order_by);
}
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Corresponding XML is defined as follows:

<select id="getAllUsers" resultType="org.javaboy.helloboot.bean.User">
    select * from user
    <if test="order_by!=null and order_by!=''">
        order by ${order_by} desc
    </if>
</select>
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Front three, very easy to understand, I believe that many small partners also know all that, in addition to these three common scenarios, there is a special scene, has often been ignored.

Fourth, it is dynamic SQL, if you use parameters in dynamic SQL as a variable, you also need to @Param notes, even if you have only one argument.

If we use in dynamic SQL parameters as judge the conditions, then we must also add @Param notes, for example, the following method:

@Mapper
public interface UserMapper {
    List<User> getUserById(@Param("id")Integer id);
}
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SQL definitions out as follows:

<select id="getUserById" resultType="org.javaboy.helloboot.bean.User">
    select * from user
    <if test="id!=null">
        where id=#{id}
    </if>
</select>
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This case, even if there is only one parameter, also need to add @Param notes, and this situation has often been overlooked!

Well, I do not know if you have to GET it? There are discussion questions please leave a message.

Public concern number [south] a little rain, focused on Spring Boot + Micro service and front and rear ends of separation full stack technology, video tutorials on a regular basis to share concerns reply after Java, Java dry Song Ge receive carefully prepared for you!

MyBatis annotations in @Param four usage scenarios, the last one often overlooked!

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