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Hibernate / MyBatis Interview questions

What is a Mapper XML file?

A Mapper XML file defines the actual SQL statements for a given mapper namespace, associating each statement with an id that corresponds to a method on the matching Mapper interface, along with the parameter and result type information MyBatis needs to bind inputs and map outputs correctly.

<mapper namespace="com.example.mapper.UserMapper">
  <select id="selectUserById" parameterType="int" resultType="com.example.model.User">
    SELECT id, name, email FROM users WHERE id = #{id}
  </select>
</mapper>

The namespace attribute must match the fully-qualified name of the corresponding Mapper interface, and each statement's id must match a method name on that interface exactly — this naming correspondence is how MyBatis links a Java method call to the specific SQL statement that should execute when that method is invoked.

Beyond simple statements like the example above, Mapper XML files also support dynamic SQL elements (<if>, <foreach>, <choose>) and complex result mappings (<resultMap>) for nested objects and collections, which is where much of MyBatis's flexibility for handling non-trivial queries and mappings actually lives.

What must a Mapper XML file's namespace match?
What must a statement's id match?

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What is MyBatis? What is the purpose of MyBatis? What are the key features of MyBatis? What is the difference between MyBatis and Hibernate? What is a SqlSessionFactory in MyBatis? What is a SqlSession in MyBatis? What is a Mapper interface in MyBatis? What is the mybatis-config.xml file used for? What is a Mapper XML file? How do you write a basic SELECT statement in MyBatis? What is parameter binding in MyBatis? What is result mapping? What are the supported statement types in MyBatis? What is the difference between #{} and ${} in MyBatis? What is a resultMap? How do you configure a data source in MyBatis? What is MyBatis-Spring? How do you integrate MyBatis with Spring Boot? What is dynamic SQL in MyBatis? List the dynamic SQL elements available in MyBatis? What is the difference between MyBatis and JPA/Hibernate in terms of philosophy? Why is #{} preferred over ${} for parameter binding? How does MyBatis prevent SQL injection? What is the difference between resultType and resultMap? What is the @Param annotation used for in MyBatis? Explain how MyBatis handles one-to-many mappings? Explain how MyBatis handles many-to-one mappings? What is the difference between association and collection in resultMap? What is lazy loading in MyBatis, and how do you configure it? Explain the lifecycle of a SqlSession? What is the difference between SqlSessionFactory and SqlSessionFactoryBuilder? How does MyBatis's first-level cache work? How does MyBatis's second-level cache work? What is the difference between first-level and second-level cache? Explain how to implement a custom TypeHandler in MyBatis? What is the purpose of the if, choose, when, otherwise dynamic SQL elements? Explain the internal working of the foreach element for batch operations? How do you handle batch inserts/updates in MyBatis? What is the Mapper proxy pattern, and how does MyBatis use it internally? Explain the execution flow of a MyBatis query from mapper call to result? What is the difference between MyBatis annotations and XML mapping? How do you use MyBatis with multiple data sources? Explain the role of the Executor in MyBatis's internal architecture, including the SIMPLE, REUSE, and BATCH executor types? How does MyBatis handle transactions, and how does it integrate with Spring's transaction management? What is a plugin/interceptor in MyBatis, and how do you write one? Explain how pagination is typically implemented in MyBatis? What is the N+1 select problem, and how does it relate to MyBatis? How do you troubleshoot a MyBatis mapping exception? Explain the internal working of MyBatis's dynamic SQL parsing? Explain the execution flow of MyBatis-Spring-Boot-Starter's auto-configuration?
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