How Mybatis uses dynamic SQL-foreach to traverse collections and bulk insert
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Bulk inserting data into the database is used very frequently during development, and it is impossible for us to insert data one by one in order to save time and improve efficiency; therefore, mybatis provides developers with foreach tags.
The foreach tag explains: collection= "": indicates the collection to traverse
Item= "": assigns the currently traversed element to the specified variable
Separator= "": the separator between each element
Open= "(": all results traversed start with the opening parenthesis
Close= ")"; all results traversed end with a closing parenthesis
Index= ""; index when traversing List, item is value; when traversing map, key,item is value
1. [foreach traversal collection]
Code-mapper class:
/ / Test foreach: traversing
Public List getEmpByConditionForeach (List emp)
Mapper mapping file:
Select * from xjinfo where XH in
# {item}
Test the code:
@ Test
Public void testSelectForeach () throws IOException {
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory ()
SqlSession openSession = sqlSessionFactory.openSession ()
Try {
EmployeemapperDynamicSQL mapper = openSession.getMapper (EmployeemapperDynamicSQL.class)
List emps = mapper.getEmpByConditionForeach (Arrays.asList ("2017000001", "2017000002", "2017000003"))
For (Employee emp: emps) {
System.out.println (emp)
}
} finally {
OpenSession.close ()
}
}
View the console print:
2. [foreach batch insert]
Code-mapper class:
/ / Test foreach: batch insert
Public void addEmpByBatchForeach (@ Param ("emps") List emps)
Mapper mapping file:
Insert into xjinfo (XH,XM,YJSLB)
Values
(# {emp.xh}, # {emp.xm}, # {emp.yjslb})
[explanation]: the annotation @ Param ("emps") in the Mapper class is that emps can be used directly in collection in foreach
Test the code:
@ Test
Public void testBatchInsert () throws IOException {
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory ()
SqlSession openSession = sqlSessionFactory.openSession ()
Try {
EmployeemapperDynamicSQL mapper = openSession.getMapper (EmployeemapperDynamicSQL.class)
List emps = new ArrayList ()
Emps.add (new Employee ("2017000000", "Li Yi", "Shuo")
Emps.add ("2017000001", "Li er", "Bo"))
Mapper.addEmpByBatchForeach (emps)
/ / Don't forget to submit when executing insert update
OpenSession.commit ()
} finally {
OpenSession.close ()
}
}
View the console print:
Finally, sort out the idea: start with the test test class, pass a list emps into the emps of the mapper class, and emps receive it in the mapping file, each time you traverse the emps, the value emp assigned to the item, and then receive the parameters in foreach with # (emp.xh).
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