Encapsulate MyBatis   Output results

resultType

Resulttype: execute sql to get the type of ResultSet conversion, using the fully qualified name or alias of the type. Note that if a collection is returned, it should be set to the type contained in the collection, not the collection itself. resultType    And resu   ltMap cannot be used at the same time.

A. Simple type

Interface method:

int countStudent();

mapper File:

< select id="countStudent" 

        resultType="int"> select count(*) from 

        student

< /select>
Copy code

Test method:

@Test

public void testRetunInt(){

        int count = studentDao.countStudent(); 

        System.out.println("Total number of students:"+ count);

}
Copy code

B. Object type

Interface method:

Student selectById(int id);

mapper file:

<select id="selectById" 

        resultType="com.bjpowernode.domain.Student"> select 

        id,name,email,age from student where id=#{studentId}

</select>
Copy code

Frame processing: create objects using construction methods. Call setXXX to assign a value to the property.

Student student = new Student();

Note: the Dao interface method returns a collection type. You need to specify the type in the collection, not the collection itself.

C,Map

The query result of sql is used as the key and value of map. Map < object, Object > is recommended.

Note: Map is the return value of the interface, and the query result of sql statement can only have one record at most. Greater than one record is an error.

Interface method:

Map<Object,Object> selectReturnMap(int id);

mapper file:

<select id="selectReturnMap" resultType="java.util.HashMap"> 

       select name,email from student where id = #{studentId}

</select>
Copy code

Test method:

@Test

public void testReturnMap(){

        Map<Object,Object> retMap = studentDao.selectReturnMap(1002);   

        System.out.println("The query result is Map:"+retMap);

}
Copy code

resultMap

resultMap can customize the mapping relationship between sql results and java object attributes. More flexible assignment of column values to specified attributes.

It is often used when the column name is different from the java object attribute name.

Usage:

1. Define resultMap first and specify the corresponding relationship between column name and attribute.

2. Replace resultType with resultMap in < Select >.

Interface method:

List< Student> selectUseResultMap(QueryParam param);

mapper file:

Test method:

Entity class attribute names and column names are handled differently

(1)   Use column aliases and < resulttype >

Steps:

one   Create a new entity class PrimaryStudent

two   Interface method

List< PrimaryStudent> selectUseFieldAlias(QueryParam param);

three   mapper   File:

four   test method

(2)   Use < resultmap >

Steps:

one   Interface method

List<PrimaryStudent> selectUseDiffResultMap(QueryParam param);

two   mapper   File:

3. Test method

Fuzzy like

There are two ways to implement fuzzy query. One is to add "%" to the query data in java code;   The second is in mapper   File sql   Add '%' to the conditional position of the statement

Demand: query names with "force"

Example 1: the "% force%" to be queried is provided in the Java code

Interface method:

List<Student> selectLikeFirst(String name);

mapper file:

<select id="selectLikeFirst" 

        resultType="com.bjpowernode.domain.Student"> select 

        id,name,email,age from student

        where name like #{studentName}

</select>
Copy code

Test method:

@Test

public void 

        testSelectLikeOne(){ String 

        name="%power%";

        List<Student> stuList = studentDao.selectLikeFirst(name); 

        stuList.forEach( stu -> System.out.println(stu));

}
Copy code

Example 2: use like name "%" #{xxx} "%" in mapper file

Interface method:

List<Student> selectLikeSecond(String name);

mapper file:

<select id="selectLikeSecond"

        resultType="com.bjpowernode.domain.Student"> select id,name,email,age 

       from student

       where name like "%" #{studentName} "%"

</select>
Copy code

Test method:

@Test

public void 

        testSelectLikeSecond(){ String 

        name="power";

        List<Student> stuList = studentDao.selectLikeSecond(name); 

        stuList.forEach( stu -> System.out.println(stu));

} 

Author: Ling Xiaoke
Link: https://juejin.cn/post/7021350272463011870