2020 Interview still confused by MyBatis? Check out these 27 interview questions! (With answers and mind maps)

preface

MyBatis interview questions

1. What is Mybatis?

2. Advantages of Mybaits:

3. Disadvantages of MyBatis framework:

4, MyBatis framework applicable occasions:

5. What are the differences between MyBatis and Hibernate?

What is the difference between #{} and ${}?

7, What if the name of the attribute in the entity class is different from the name of the field in the table?

<select ID = "selectOrder" parameterType = "int" resulteType = "me.gacl.domain.order" > select order_id ID, order_no orderno ,order_price price form orderswhere order_id=#{id};
</select>Copy the code

<select id="getOrder" parameterType="int"
resultMap="orderresultmap">
select * from orders where order_id=#{id}
</select>
<resultMap type= "me. Gacl. Domain. The order" id = "orderresultmap" > <! > < ID property= "ID" column= "order_id" > <! -- Use the result attribute to map non-primary key fields. Property is the name of the entity class attribute. Column is an attribute in the data table -- > <result property= "orderno" column= "order_no" /> <result property= "price" column= "order_price" /> </reslutMap>Copy the code

8, fuzzy query like statement how to write?

Smi string wildcardname = "% %"; list<name> names = mapper.selectlike(wildcardname); <select id= "selectlike" > select * from foowhere bar like #{value}
</select>Copy the code

String wildcardname = "smi"; list<name> names = mapper.selectlike(wildcardname); <select id= "selectlike" > select * from foowhere bar like "%"#{value}"%"
</select>Copy the code

9. Usually, an Xml mapping file will write a Dao interface corresponding to it. What is the working principle of this Dao interface? Can methods in the Dao interface be overloaded if their parameters are different?

How does Mybatis paginate? How does paging plug-ins work?

How does Mybatis encapsulate SQL execution results as target objects and return them? What are the mappings?

How do I perform batch inserts?

<insert ID = "insertname" > insert into names (name) values (# {
	value
}
)
</insert>Copy the code

list < string > names = new arraylist(); Names. The add (" Fred "); Names. The add (" barney "); Names. The add (" Betty "); Names. The add (" Wilma "); / / note here executortype. Batch sqlsession sqlsession = sqlsessionfactory. Opensession (executortype. Batch); try { namemapper mapper = sqlsession.getmapper(namemapper.class);for (string name: names) {
		mapper.insertname(name);
	}
	sqlsession.commit();
}
catch (Exception e) {
	e.printStackTrace();
	sqlSession.rollback();
	throw e;
}
finally {
	sqlsession.close();
}Copy the code

13. How to obtain the automatically generated (primary) key value?

< insert insertname usegeneratedkeys = "id =" "true"Keyproperty =" id "> insert into names (name) values (# {name } ) </insert> name name = new name(); Name. Elegantly-named setname (" Fred "); int rows = mapper.insertname(name); // When done, the ID has been set to the object system.out.println(" rows = "+ rows); System.out. println(" generated key value = "+ name.getid());Copy the code

14. How to pass multiple parameters in Mapper?

<select id="selectUser"resultMap="BaseResultMap">
select * fromuser_user_t whereuser_name = # {0}
anduser_area=# {1}
</select>Copy the code

Public interface usermapper {user selectUser (@param(" username ") string username,@param(" hashedPassword ") string hashedpassword); }Copy the code

<select ID = "selectUser" resultType = "user" > select ID, username, hashedPassword from some_tablewhere username = #{username}
and hashedpassword = #{hashedpassword}
</select>Copy the code

Try {// Map the file namespace. // Since we have more than two parameters, and only one Object parameter is collected in the method, So we use the Map collection to load our parameters Map < String, Object > Map = new HashMap(); map.put("start", start);
	map.put("end", end);
	return sqlSession.selectList("StudentID.pagination", map);
}
catch (Exception e) {
	e.printStackTrace();
	sqlSession.rollback();
	throw e;
}
finally {
	MybatisUtil.closeSqlSession();
}Copy the code

15, Mybatis dynamic SQL what to use? How does it work? What dynamic SQL is there?

16, Xml mapping file, in addition to the common select | insert | updae | delete tags, what other tags?

17. In the Xml mapping files of Mybatis, can the IDS of different Xml mapping files be repeated?

Why Mybatis is a semi-automatic ORM mapping tool? What’s the difference between it and automatic?

19, one to one, one to many associated query?

<mapper namespace="com.lcb.mapping.userMapper"> <! --association one-to-one associative query --> <select id="getClass" parameterType="int"
resultMap="ClassesResultMap">
select * from class c,teacher t where c.teacher_id=t.t_id and
c.c_id=#{id}
</select>
<resultMap type="com.lcb.user.Classes" id="ClassesResultMap"> <! -- mapping entity class field names to data table field names --> <id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher"
javaType="com.lcb.user.Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/> </association> </resultMap> <! --collection 1 to many associative query --> <select id="getClass2" parameterType="int"
resultMap="ClassesResultMap2">
select * from class c,teacher t,student s where c.teacher_id=t.t_id
and c.c_id=s.class_id and c.c_id=#{id}
</select>
<resultMap type="com.lcb.user.Classes" id="ClassesResultMap2">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher"
javaType="com.lcb.user.Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
<collection property="student"
ofType="com.lcb.user.Student">
<id property="id" column="s_id"/>
<result property="name" column="s_name"/>
</collection>
</resultMap>
</mapper>Copy the code

20. How many ways can MyBatis achieve one-to-one? How does it work?

21, MyBatis has several ways to achieve one-to-many, how to operate?

Does Mybatis support lazy loading? If so, how does it work?

23, Mybatis level 1, level 2 cache:

24, What is MyBatis interface binding? What are the implementation methods?

25. What are the requirements when using Mapper interface of MyBatis?

26. What are the ways to write Mapper?

<mappers>
<mapper resource="Address of mapper. XML file" />
<mapper resource="Address of mapper. XML file" />
</mappers>Copy the code

<bean id="" class="Implementation of mapper Interface">
<property name="sqlSessionFactory"
ref="sqlSessionFactory"></property>
</bean>Copy the code

<mappers>
<mapper resource="Address of mapper. XML file" />
<mapper resource="Address of mapper. XML file" />
</mappers>Copy the code

<bean id="" class="org.mybatis.spring.mapper.MapperFactoryBean">
<property name="mapperInterface" value="Mapper interface address" />
<property name="sqlSessionFactory" ref="sqlSessionFactory" />
</bean>Copy the code

<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="Mapper interface packet address"></property>
<property name="sqlSessionFactoryBeanName"
value="sqlSessionFactory"/>
</bean>Copy the code

27. Describe the operation principle of Mybatis plug-in and how to write a plug-in.

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