mybatis WhenPresent

In MyBatis, the "whenPresent" tag is used in the `<set>` element of an update statement to conditionally update a column if the corresponding property is not null. It provides a way to dynamically include or exclude columns from the update statement based on their values.

Here's an example of how to use the "whenPresent" tag in MyBatis:

<update id="updateUser" parameterType="User">
  UPDATE users
  <set>
    <if test="name != null">
      name = #{name},
    </if>
    <if test="age != null">
      age = #{age},
    </if>
  </set>
  WHERE id = #{id}
</update>

In this example, the `name` and `age` columns are conditionally updated based on the values of the `name` and `age` properties of the `User` object. If either of the properties is not null, the corresponding column will be included in the update statement.

I hope this helps! Let me know if you have any further questions.