如何正确使用Mybatis的@Param批注 [英] How to properly use the @Param annotation of Mybatis

问题描述

起初我没有使用@Param注释，这是我的mapper.java

I didn't use @Param annotation at first, this is my mapper.java

public void changeUserAuth(Integer userId,int identity);

，这是我的mapper.xml

, and this is my mapper.xml

<update id="changeUserAuth">
    update user
    <set>
        <if test="identity != 0">identity = #{identity}</if>
    </set>
    <where>
        <if test="userId != 0">userId = #{userId}</if>
    </where>
</update>

然后它可以正常工作！我继续这样写，如下:

then it works correctly!I continue to write like this, as follows:

//this's mapper.java
public void updateUserStatus(Integer userId);

<!--this is mapper.xml>
<update id="changeUserAuth">
    update user
    set deleteFlag= true
    <where>
        <if test="userId != 0">userId = #{userId}</if>
    </where>
</update>

但是，它给出了一个错误，消息是

however,it gave an error,the message is

"class.java.lang.Integer"中没有名为"userId"的属性的吸气剂.

There is no getter for property named 'userId' in 'class.java.lang.Integer'

我可以理解mybatis无法解析Integer，但是为什么它不是像我第一次使用时那样的错误，仅仅是因为我有一个int类型的Parameter?在第二种方法中，我必须使用@Param注释

I can understand that mybatis cannot parse the Integer, but why it is not an error like my first use, just because I have an int type Parameter? In the second method, I have to use @Param annotation

推荐答案

以下是在MyBatis语句中引用参数的方式.

Here is how you reference parameters in MyBatis statements.

在下面的说明中，我将使用此POJO.

I'll use this POJO in the following explanation.

public class User {
  private Integer id;
  private String name;
  //...
}

---

使用@Param时

如果在参数上添加@Param批注，则可以使用指定的名称来引用该参数.这是最简单的情况.

---

When @Param is used

If you add @Param annotation on a parameter, you can use the specified name to reference the parameter. This is the simplest case.

一些例子:

List<USer> select(@Param("id") Integer userId, @Param("name") String userName);

void insert(@Param("record") User user);

<select id="select" resultType="User">
  select * from users
  <where>
    <if test="id != null">and id = #{id}</if>
    <if test="name != null">and name = #{name}</if>
  </where>
</select>

<insert id="insert">
  insert into users (id, name) values
    (#{record.id}, #{record.name})
</insert>

没有@Param

如果没有@Param，则取决于几个条件.

Without @Param

If there is no @Param, it depends on several conditions.

1. ...唯一的参数可分配给java.util.List，您可以将参数引用为list.

1. ... the sole parameter is assignable to java.util.List, you can reference the parameter as list.

List<User> selectByIds(List<Integer> ids);

<select id="select" resultType="User">
  select * from users
  where id in (
    <foreach item="x" collection="list" separator=",">
      #{x}
    </foreach>
  )
</select>

...唯一的参数可分配给java.util.Collection，您可以将参数引用为collection.

... the sole parameter is assignable to java.util.Collection, you can reference the parameter as collection.

List<User> selectByIds(Set<Integer> ids);

<select id="select" resultType="User">
  select * from users
  where id in (
    <foreach item="x" collection="collection" separator=",">
      #{x}
    </foreach>
  )
</select>

...有一个映射到唯一参数的类型处理程序(即参数为String，Integer等).

... there is a type handler mapped to the sole parameter (i.e. the parameter is String, Integer, etc.).

• 在MyBatis 3.5.2和更高版本中，您可以使用任何名称引用该参数(不过，出于明显的原因，您应该使用明智的名称).例如

• With MyBatis 3.5.2 and later, you can reference the parameter using any name (you should use sensible names for obvious reasons, though). e.g.

List<User> select(Integer id);

<select id="select" resultType="User">
  select * from users
  <where>
    <if test="x != null">and id = #{y}</if>
  </where>
</select>

使用MyBatis 3.5.1

With MyBatis 3.5.1

• 您可以在#{}中使用任何名称引用该参数.
• 必须在${}，<if />和<when />的test属性以及<bind />的value属性中将参数引用为_parameter.这就是第二个示例引发异常的原因.

• you can reference the parameter with any name in #{}.
• you must reference the parameter as _parameter in ${}, test attribute of <if /> and <when /> and value attribute of <bind />. This is why your second example throws exception.

List<User> select(Integer id);

<select id="select" resultType="User">
  select * from users
  <where>
    <if test="_parameter != null">and id = #{z}</if>
  </where>
</select>

...没有映射到唯一参数的类型处理程序(即，参数为POJO或Map<String, ?>)，您可以直接使用其名称(或如果参数为a的键)引用参数属性Map).

... there is no type handler mapped to the sole parameter (i.e. the parameter is POJO or Map<String, ?>), you can reference the parameter properties directly with their names (or the keys if the parameter is a Map).

void insert(User user);

<insert id="insert">
  insert into users (id, name) values
    (#{id}, #{name})
</insert>

当mapper方法采用多个参数时

1. 如果项目是使用'-parameters'编译的

1. If the project is compiled with '-parameters' compiler option, you can reference the parameters using their names declared in the method signature. This is your first example.

List<USer> select(Integer userId, String userName);

<select id="select" resultType="User">
  select * from users
  <where>
    <if test="id != null">and id = #{id}</if>
    <if test="name != null">and name = #{name}</if>
  </where>
</select>

否则，您可以使用MyBatis隐式指定的名称来引用参数，即arg0，arg1，...(我不建议这样做，因为它易碎且容易出错).

Otherwise, you can reference the parameters using the names implicitly assigned by MyBatis i.e. arg0, arg1, ... (I would not recommend this as it's fragile and error-prone).

List<USer> select(Integer userId, String userName);

<select id="select" resultType="User">
  select * from users
  <where>
    <if test="arg0 != null">and id = #{arg0}</if>
    <if test="arg1 != null">and name = #{arg1}</if>
  </where>
</select>

---

[1] RowBounds和ResultHandler不计算在内.

---

[1] RowBounds and ResultHandler does not count.

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