mybatis if else

MyBatis provides support for conditional logic using the `<if>` and `<choose>` elements. These elements allow you to conditionally include or exclude parts of your SQL statements based on certain conditions.

The `<if>` element is used to conditionally include a part of the SQL statement. It takes a test attribute that specifies the condition to be evaluated. If the condition evaluates to true, the content inside the `<if>` element is included in the SQL statement.

Here's an example of using the `<if>` element in MyBatis:

<select id="getUserById" resultType="User">
  SELECT *
  FROM users
  WHERE id = #{id}
    <if test="name != null">
      AND name = #{name}
    </if>
</select>

In this example, the `name` parameter is optional. If it is provided, the condition `name != null` evaluates to true, and the `AND name = #{name}` part is included in the SQL statement. If the `name` parameter is not provided or is null, that part is excluded.

The `<choose>` element is used to implement if-else logic. It contains one or more `<when>` elements and an optional `<otherwise>` element. The `<when>` elements specify conditions, and the content inside the first matching `<when>` element is included in the SQL statement. If none of the conditions evaluate to true, the content inside the `<otherwise>` element is included.

Here's an example of using the `<choose>` element in MyBatis:

<select id="getUserByCondition" resultType="User">
  SELECT *
  FROM users
  WHERE
    <choose>
      <when test="id != null">
        id = #{id}
      </when>
      <when test="name != null">
        name = #{name}
      </when>
      <otherwise>
        status = 'active'
      </otherwise>
    </choose>
</select>

In this example, the SQL statement will include either `id = #{id}` if the `id` parameter is provided, or `name = #{name}` if the `name` parameter is provided. If neither parameter is provided, the SQL statement will include `status = 'active'` as a default condition.

These conditional elements provide flexibility in constructing dynamic SQL statements based on different conditions in your application.