Mybatis_sql Mapping (2)

Article excerpt from: http://blog.csdn.net/y172158950/article/details/172583771. SQL reuse: Defines a SQL fragment that can be reused in any SQL statement. [Java]View PlainCopy

1. <sql id="Personcolumns" > Name, Sex, updatetime</sql>
2. <select id="Selectperson" parametertype="int" resulttype="HashMap" >
3. Select ID, <include refid="Personcolumns"/> from the person where ID =#{id};
4. </select>

2. JavaBean aliases: Do not write the package path every time [Java]View PlainCopy

1. <!--in Config XML file, defined--
2. <typealias type= "Com.someapp.model.User" alias= "User"/>
3. <!--in SQL Mapping XML file, using--
4. <select id= "Selectusers" parametertype= "int" resulttype= "User" >
5. Select ID, username, hashedpassword from some_table where id = #{id}
6. </select>

3. Table and entity column names that do not match the alias of a) SQL [Java]View PlainCopy

1. <select id= "Selectusers" parametertype= "int" resulttype= "User" >
2. Select user_id as "id", user_name as UserName, Hashed_password as Hashedpassword from some_table where id = #{id}
3. </select>

b) define the external Resultmap [Java]View PlainCopy

2. <resultmap id="Userresult" type="User" >
4. <id property="id" column="_id"/>
6. <result property="name" column="_name"/>
8. <result property="password" column="_password"/>
10. </resultMap>
14. <select id="Selectuser" parametertype="int" resultmap="Userresult" >
16. Select _id, _name, _password from _user where _id =#{id};
18. </select>

c) Exception and resolution: [Java]View PlainCopy

2. Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException:
4. # # # Error Building sqlsession.
6. # # # The error may exist in Com/yjq/entity/user.xml
8. # # # The error occurred while processing Mapper_resultmap[userresult]
10. # # # Cause:org.apache.ibatis.builder.BuilderException:Error parsing SQL Mapper Configuration. Cause:java.lang.RuntimeException:Error parsing Mapper XML. Cause:org.apache.ibatis.builder.BuilderException:Error resolving class.  Cause:org.apache.ibatis.type.TypeException:Could not resolve type alias ' Userresult '. Cause:java.lang.ClassNotFoundException:Cannot Find class:userresult
12. At Org.apache.ibatis.exceptions.ExceptionFactory.wrapException (Exceptionfactory.java:8)
14. At Org.apache.ibatis.session.SqlSessionFactoryBuilder.build (Sqlsessionfactorybuilder.java: +)
16. At Org.apache.ibatis.session.SqlSessionFactoryBuilder.build (Sqlsessionfactorybuilder.java: +)
18. At Com.yjq.db.DbFactory.getInstance (Dbfactory.java:)
20. At Com.yjq.dao.UserDao.selectUserById (Userdao.java:)
22. At Com.yjq.dao.UserDao.main (Userdao.java:)
24. caused By:org.apache.ibatis.builder.BuilderException:Error parsing SQL Mapper Configuration. Cause:java.lang.RuntimeException:Error parsing Mapper XML. Cause:org.apache.ibatis.builder.BuilderException:Error resolving class.  Cause:org.apache.ibatis.type.TypeException:Could not resolve type alias ' Userresult '. Cause:java.lang.ClassNotFoundException:Cannot Find class:userresult
26. At Org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration (Xmlconfigbuilder.java:)
28. At Org.apache.ibatis.builder.xml.XMLConfigBuilder.parse (Xmlconfigbuilder.java:)
30. At Org.apache.ibatis.session.SqlSessionFactoryBuilder.build (Sqlsessionfactorybuilder.java: +)
32. ... 4 More
34. caused By:java.lang.RuntimeException:Error parsing Mapper XML. Cause:org.apache.ibatis.builder.BuilderException:Error resolving class.  Cause:org.apache.ibatis.type.TypeException:Could not resolve type alias ' Userresult '. Cause:java.lang.ClassNotFoundException:Cannot Find class:userresult
36. At Org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement (Xmlmapperbuilder.java:)
38. At Org.apache.ibatis.builder.xml.XMLMapperBuilder.parse (Xmlmapperbuilder.java:)
40. At Org.apache.ibatis.builder.xml.XMLConfigBuilder.mapperElement (Xmlconfigbuilder.java:255)
42. At Org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration (Xmlconfigbuilder.java:)
44. ... 6 More
46. caused By:org.apache.ibatis.builder.BuilderException:Error resolving class.  Cause:org.apache.ibatis.type.TypeException:Could not resolve type alias ' Userresult '. Cause:java.lang.ClassNotFoundException:Cannot Find class:userresult
48. At Org.apache.ibatis.builder.BaseBuilder.resolveClass (Basebuilder.java:)
50. At Org.apache.ibatis.builder.xml.XMLStatementBuilder.parseStatementNode (Xmlstatementbuilder.java: +)
52. At Org.apache.ibatis.builder.xml.XMLMapperBuilder.buildStatementFromContext (Xmlmapperbuilder.java:)
54. At Org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement (Xmlmapperbuilder.java:)
56. ... 9 More
58. caused by:org.apache.ibatis.type.TypeException:Could not resolve type alias ' Userresult '. Cause:java.lang.ClassNotFoundException:Cannot Find class:userresult
60. At Org.apache.ibatis.type.TypeAliasRegistry.resolveAlias (Typealiasregistry.java:)
62. At Org.apache.ibatis.builder.BaseBuilder.resolveAlias (Basebuilder.java:)
64. At Org.apache.ibatis.builder.BaseBuilder.resolveClass (Basebuilder.java:)
66. ... More
68. caused By:java.lang.ClassNotFoundException:Cannot find Class:userresult
70. At Org.apache.ibatis.io.ClassLoaderWrapper.classForName (Classloaderwrapper.java:173)
72. At Org.apache.ibatis.io.ClassLoaderWrapper.classForName (Classloaderwrapper.java:)
74. At Org.apache.ibatis.io.Resources.classForName (Resources.java:235)
76. At Org.apache.ibatis.type.TypeAliasRegistry.resolveAlias (Typealiasregistry.java:)
78. ... More

<select id= "Selectuser" parametertype= "int" resulttype= "Userresult" > Modified to Resultmap

Mybatis_sql Mapping (2)