Three, MyBatis series: Mapper mapping to read database records by Mapper mapping file

When you use MyBatis to fetch records from a database, you write only one mapping XML file. This is the strength of mybatis, which is said to save 95% more code than normal JDBC.
First to see how to obtain records, engineering configuration, please refer to the "one, MyBatis series: The First MyBatis project":

1. Mapper Configuration file contents

1 <?XML version= "1.0" encoding= "UTF-8"?>2 <!DOCTYPE Mapper Public "-//mybatis.org//dtd mapper 3.0//en"3 "Http://mybatis.org/dtd/mybatis-3-mapper.dtd">4 <Mappernamespace= "Test">5     <SelectID= "Getuserbyid"ParameterType= "int"Resulttype= "Map">6 SELECT * FROM user where id = #{value}7     </Select>8     <SelectID= "Getusers"Resulttype= "Map">9 SELECT * from userTen     </Select> One </Mapper>

Understand the node elements:

• Mapper: The root node of the mapping file, all configurations are filled in;
• Namespace: The namespace to which the mapping belongs;
• Select: Represents the section used to read records;
  • ID: The unique identifier under the namespace;
  • ParameterType: The type of the parameter passed in the SQL statement, the types that can be received are simple types, pojo types, map types, and so on;
  • Resulttype: The return type of the statement can be a simple type, a pojo type, a map type, and so on;
  • SELECT * FROM User: A standard SQL statement written by a user to query for desired results;
  • #{value}: If the parameter type passed in is a simple type, then value can be written in any letter;

Note that ParameterType does not accept multiple parameters, and if more than one parameter is present, it needs to be encapsulated as a POJO type.

2. Write a unit test to read the data record

1 @Test2  Public voidGetuserstest ()throwsIOException {3InputStream stream = Resources.getresourceasstream ("Mybatisconfig.xml");4Sqlsessionfactory factory =NewSqlsessionfactorybuilder (). Build (stream);5Sqlsession sqlsession =factory.opensession ();6     Try {7         //reads a record and returns the MAP result type.8Map<object, object> user = Sqlsession.selectone ("Test.getuserbyid", 1);9 System.out.println (user);Ten          One         //reads more than one record, returning the list<map> result type. AList<map<object, object>> users = sqlsession.selectlist ("Test.getusers"); - System.out.println (users);  -}finally { the sqlsession.close (); -     } -}

To view the log output:

DEBUG [main]-Logging initialized using ' class Org.apache.ibatis.logging.log4j.Log4jImpl ' adapter.
DEBUG [main]-Pooleddatasource forcefully closed/removed all connections.
DEBUG [main]-Opening JDBC Connection
DEBUG [main]-Created connection 603650290.
DEBUG [main]-Setting autocommit to False on JDBC Connection [[email protected]]
DEBUG [main]-==> preparing:select * from user where id =?
DEBUG [main]-==> parameters:1 (Integer)
DEBUG [main]-<== total:1
{birthday=2014-07-10, address= Beijing, sex=2, id=1, username= Harry, attrs={"Parameter 1": "Parameter value 1"}}
DEBUG [main]-==> preparing:select * from user
DEBUG [main]-==> Parameters:
DEBUG [main]-<== total:6
[{birthday=2014-07-10, address= Beijing, sex=2, id=1, username= Harry, attrs={"Parameter 1": "Parameter value 1"}}, {birthday=2014-07-10, address= BEIJING, Sex=1, id=10, Username= Zhang San, attrs={"Parameter 1": "Parameter value 1"}}, ... "
DEBUG [main]-resetting autocommit to True on JDBC Connection [[email protected]]
DEBUG [main]-Closing JDBC Connection [[email protected]
DEBUG [main]-returned connection 603650290 to pool.

Three, MyBatis series: Mapper mapping to read database records by Mapper mapping file