How is the if-else usage in MyBatis?

1 year ago
Liam
1 minute

In MyBatis, you can use the element to implement conditional judgments. This element can dynamically add conditional statements in SQL queries based on certain conditions.

The sample code is shown below:

<select id="selectUsers" parameterType="map" resultType="User">
  SELECT * FROM users
  <where>
    <if test="username != null">
      AND username = #{username}
    </if>
    <if test="age != null">
      AND age = #{age}
    </if>
  </where>
</select>

In the given example, two conditional statements, “AND username = #{username}” and “AND age = #{age}”, were dynamically added based on the conditions.

If both the username and age are not empty, the SQL statement will look something like this:

SELECT * FROM users
WHERE username = ? AND age = ?

If the username is empty and the age is not empty, the SQL statement will look something like this:

SELECT * FROM users
WHERE age = ?

If the username is not empty and the age is empty, the SQL statement will be something like this:

SELECT * FROM users
WHERE username = ?

Using the element allows for dynamically constructing SQL statements based on conditions, which is very useful in practical development.

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