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This article mainly introduces "the use of mybatis-plus". In the daily operation, I believe that many people have doubts about the use of mybatis-plus. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful for you to answer the doubts about the use of mybatis-plus. Next, please follow the editor to study!

Foreword:

With regard to the introduction and basic use of mybatis-plus, I have already introduced it in the article "getting started with mybatis-plus", which I will not repeat here. This paper mainly explains the knowledge points of mybatis-plus, such as AR mode, plug-ins, reverse engineering, custom global operation, automatic filling of common fields and so on.

1. ActiveRecord:

Active Record (activity record) is a domain model schema characterized by a model class corresponding to a table in a relational database and an instance of the model class corresponding to a row record in the table. ActiveRecord has always been widely loved by dynamic languages (PHP, Ruby, etc.). As a quasi-static language, Java can only lament the elegance of ActiveRecord, so MP has also made some exploration on the road of AR. It only needs to let the entity class inherit the Model class and implement the primary key assignment method to start the journey of AR. Next, let's look at the specific code:

1 、 entity:

@ Datapublic class User extends Model {private Integer id; private String name; private Integer age; private Integer gender; / / override this method, the primary key of the current class of return @ Override protected Serializable pkVal () {return id;}}

Note: entity class inherits Model class and overrides pkVal method.

2 、 mapper:

Public interface UserDao extends BaseMapper {}

Note: although this interface is not used in AR mode, it must be defined, otherwise a null pointer exception will be reported when using AR.

3. Use AR:

(1) AR insertion operation:

RunWith (SpringJUnit4ClassRunner.class) @ ContextConfiguration ({"classpath:spring/spring-dao.xml"}) public class TestAR {@ Test public void testArInsert () {User user = new User (); user.setName ("Lin Qingxia"); user.setAge (22); user.setGender (1); boolean result = user.insert (); System.out.println (result);}}

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Note: you can see that we don't need to inject the mapper interface, but as I just said, if you don't use it, you still have to define it, or you'll get an error. The AR operation calls the relevant method through the object itself. For example, if you want to insert a user, you can call the insert method with that user. The returned value is of Boolean type. As you can see from the figure above, true is returned, which indicates that the operation is successful.

(2) AR update operation:

@ Test public void testArUpdate () {User user = new User (); user.setId (1); user.setName ("Liu Yifei"); boolean result = user.updateById (); System.out.println (result);}

Note: user calls the updateById method to update the user whose id is 1.

(3) AR query operation:

@ Test public void testArSelect () {User user = new User (); / / 1, query / / user = user.selectById (1) according to id; / / or use / / user.setId (1); / / user = user.selectById (); / / 2, query all / / List users = user.selectAll () / / 3. Query / / List users = user.selectList (new EntityWrapper (). Like ("name", "Liu")); / / 4. Total number of eligible queries int result = user.selectCount (new EntityWrapper (). Eq ("gender", 1)); System.out.println (result);}

Note: the above code involves four different query operations, which is similar to the method provided by MP's BaseMapper, except that it is called by an entity object.

(4) AR deletion operation:

@ Test public void testArDelete () {User user = new User (); / / deleting data that does not exist in the database also returns true / / 1, delete data according to id / / boolean result = user.deleteById (1); / / or write / / user.setId (1); / / boolean result = user.deleteById () / / 2. Delete boolean result = user.delete (new EntityWrapper () .like ("name", "Ling")); System.out.println (result);}

Note: two deletion methods are introduced here, and there are comments in the code. It should be noted that deleting data that does not exist in the database will also result in true.

(5) AR paging operation:

@ Test public void testArPage () {User user = new User (); Page page = user.selectPage (new Page (1pome 4), new EntityWrapper (). Like ("name", "Liu"); List users = page.getRecords (); System.out.println (users);}

Note: this paging method, like the paging provided by BaseMapper, is memory paging, not physical paging, because limit is not used in the sql statement, just like BaseMapper's selectPage method, real physical paging can be achieved after configuring the paging plug-in. The paging method of AR is different from that provided by BaseMapper in that the selectPage method of BaseMapper returns a list collection of queried records, while the selectPage method of AR returns a page object, which encapsulates the queried information and can be obtained through the getRecords method.

Second, the configuration of plug-ins:

MP provides many easy-to-use plug-ins that are easy to configure and easy to use. Let's take a look at how the plug-in for MP is used.

1. Paging plug-in:

As mentioned earlier, neither BaseMapper's selectPage method nor the selectPage method provided by AR is physical paging, which is only after you configure the paging plug-in, so let's take a look at how to configure this plug-in now.

Note: in the bean of sqlSessionFactory, by configuring plug-ins, all subsequent plug-ins are configured in this list.

@ Test public void testPage () {/ / after configuring the paging plug-in, the selectpage method is still used as before, / / but now it is the real physical paging, with limit in the sql statement Page page = new Page (1,2); List employeeList = emplopyeeDao.selectPage (page, null); System.out.println (employeeList) System.out.println ("= relevant paging information ="); System.out.println ("Total number:" + page.getTotal ()); System.out.println ("current Page number:" + page.getCurrent ()); System.out.println ("Total pages:" + page.getPages ()); System.out.println ("display number per Page:" + page.getSize ()) System.out.println ("whether there is a previous page:" + page.hasPrevious ()); System.out.println ("whether there is a next page:" + page.hasNext ()); / / you can also set the query results into page.setRecords (employeeList) in the page object;}

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As you can see from the figure, there is already limit in the sql statement, which is physical paging.

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You can also get the relevant paging information by calling the relevant methods through page, and you can also set the query results back to the page object to facilitate the front end to use.

2. Performance analysis plug-in:

Add the following bean to the list of plugin to enable the performance analysis plug-in:

Note: this performance analysis plug-in is configured with two properties, the first is to format the sql statement, and when it is set to true, the format of the sql statement is the same as in the screenshot above; the second attribute is the maximum time for the execution of the sql statement, which will cause an error if it exceeds the value value, which means that the execution of the sql statement will stop after more than 1000 milliseconds.

3. Execute the analysis plug-in:

Note: this plug-in is configured with a property, and when stopProceed is set to true, if you delete everything in the table, an exception will be thrown and the operation will be terminated. The main purpose of the plug-in is to prevent manual shaking from mistakenly deleting data.

@ Testpublic void testSqlExplain () {/ / condition is null, that is, delete the entire table. Executing the analysis plug-in will terminate the operation emplopyeeDao.delete (null);}

When you run the junit test, you can see the following error, indicating that the plug-in is in effect.

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Third, reverse engineering of MP:

The code generator of MyBatis is generated based on xml file, which can generate entity class, Mapper interface and Mapper mapping file.

MP's code generator is generated based on Java code, which can be generated: entity classes (you can choose whether or not to support AR), Mapper interface, Mapper mapping file, Service layer, Controller layer.

1. Add dependencies:

Mysql mysql-connector-java 5.1.37 com.baomidou mybatis-plus 2.3 org.apache.velocity velocity-engine-core 2.0

Note: the above three dependencies are necessary. In order to see the generation intuitively in the console, you can add log packages (slf4j-api and slf4j-log4j2). In order to ensure that the generated code will not report errors, you can also add spring-related dependencies, lombok dependencies, and so on.

2. Sample code of generator:

/ * * @ author: zhu * @ date: 11:17 on 2018-8-20 * mybatis-plus reverse engineering sample code * / public class test {@ Test public void testGenerator () {/ / 1, global configuration GlobalConfig config = new GlobalConfig () Config.setActiveRecord (true) / / Open AR mode .setAuthor ("zhu") / set the author / / build path (usually generated under the src/main/java of this project) .setOutputDir ("E:\\ develop\\ Java\\ workspace\\ ideaworkspace\\ mpg\\ main\\ java") .setFileOverride (true) ) / / the second build will overwrite the first generation .setIdType (IdType.AUTO) / / primary key policy .setServiceName ("% sService") / / whether the generated service interface name starts with I. This setting does not have I .setBaseResultMap (true) / / generate resultMap .setBaseColumnList (true) / / generate the basic column / / 2 in xml, and configure the data source DataSourceConfig dataSourceConfig = new DataSourceConfig () DataSourceConfig.setDbType (DbType.MYSQL) / / database type .setDriverName ("com.mysql.jdbc.Driver") .setUrl ("jdbc:mysql:/// database name") .setUsername ("database user name") .setPassword ("database password") / / 3. Policy configuration StrategyConfig strategyConfig = new StrategyConfig () StrategyConfig.setCapitalMode (true) / / enables global uppercase naming. SetDbColumnUnderline (true) / Table name field names are named using underscores. SetNaming (NamingStrategy.underline_to_camel) / / underscores to humps. SetTablePrefix ("tb_") / / table name prefix. SetEntityLombokModel (true) / / use lombok .setInclude ("Table 1") "Table 2") / / Table / / 4 used in reverse engineering, package name policy configuration PackageConfig packageConfig = new PackageConfig () PackageConfig.setParent ("com.zhu.mpg") / / sets the parent .setMapper ("mapper") .setService ("service") .setController ("controller") .setEntity ("entity") .setXml ("mapper") of the package name / / set the directory of the xml file / / 5, integrate the configuration AutoGenerator autoGenerator = new AutoGenerator (); autoGenerator.setGlobalConfig (config) .setDataSource (dataSourceConfig) .setStrategy (strategyConfig) .setPackageInfo (packageConfig); / / 6, execute autoGenerator.execute ();}}

Note: the above is the sample code. As long as you run the junit test, you will generate entity, mapper interface, mapper xml file, service, serviceImpl, controller code. There are detailed comments in each setting code, which will not be repeated here.

4. Customize the global operation:

(1) AutoSqlInjector:

BaseMapper provides 17 common methods, but there are some requirements that these methods are not well implemented, so what to do? You will certainly think of writing sql statements in the xml file to solve the problem. This is really possible, because MP is only enhanced but not changed, and we can solve it in the original way of mybatis. However, MP also provides another solution, which is to customize the global operation. The so-called custom global operation, that is, we can customize some methods in mapper, and then through some actions, this custom method can also be called globally like the built-in method of BaseMapper. Let's take a look at how to implement it (take the deleteAll method as an example).

1. Define the method in the mapper API:

Public interface EmplopyeeDao extends BaseMapper {int deleteAll ();} public interface UserDao extends BaseMapper {int deleteAll ();}

The deleteAll method is defined in both mapper interfaces.

2. Write a custom injection class:

Public class MySqlInjector extends AutoSqlInjector {@ Override public void inject (Configuration configuration, MapperBuilderAssistant builderAssistant, Class mapperClass, Class modelClass, TableInfo table) {/ * add a custom method * / deleteAllUser (mapperClass, modelClass, table); System.out.println (table.getTableName ()) } public void deleteAllUser (Class mapperClass, Class modelClass, TableInfo table) {/ * execute SQL, dynamic SQL reference class SqlMethod * / String sql = "delete from" >

Note: this class inherits AutoSqlInjector and overrides the inject method. Then write the sql statement, specify the method in the mapper interface, and finally call the addDeleteMappedStatement method.

3. Configure in the spring configuration file:

Note: first register the custom class as bean, and then reference the bean of the custom class in the bean of the global policy configuration.

4. Test:

@ Testpublic void testMySqlInjector () {Integer result = userDao.deleteAll (); System.out.println (result);} @ Testpublic void testMySqlInjector2 () {Integer result = emplopyeeDao.deleteAll (); System.out.println (result);}

Note: it has been tested that when userDao calls the deleteAll method, all data in the tb_ user table is deleted, and when employeeDao calls the deleteAll method, all data in the tb_ employee table is deleted. It shows that the deleteAll method is effective. However, when running these two tests, because it is a full table delete operation, you have to turn off the execution analysis plug-in first.

(2) logical deletion:

In fact, the data will not be easily deleted, after all, data collection is not easy, so there is a logical deletion. Logical deletion: it does not actually delete the data from the database, but sets a logically deleted field in the currently deleted data to delete state. For example, if the data has a field logic_flag, a value of 1 means not deleted, and a value of-1 means deletion, then logical deletion means turning 1 into-1.

1. Data sheet:

You need to add a logical delete field (logic_flag) to the data table.

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2. Entity class:

@ Datapublic class User {private Integer id; private String name; private Integer age; private Integer gender; @ TableLogic / / tag logic delete attribute private Integer logicFlag;}

Note: the logical delete field in the database is logic_flag, so the logicFlag in the entity class needs to be marked with the @ TableLogic annotation.

3 、 mapper:

Public interface UserDao extends BaseMapper {}

4. Delete the configuration logic:

The following configuration needs to be done in spring-dao.xml:

First define the logically deleted bean:

Then inject logical deletion and logical deletion values into the globally configured bean:

Note: because logical deletion is actually a sqlInjector, you need to comment out the custom global action that was injected when you just did the custom global operation. There are detailed comments in the above code.

6. Test:

Test public void testLogicDelete () {Integer result = userDao.deleteById (1); System.out.println (result); / / User user = userDao.selectById (1); / / System.out.println (user);}

Note: when you run the test and perform the delete operation, the real sql statement executed is UPDATE tb_user SET logic_flag=-1 WHERE id=?, which sets the value of the logical delete field to-1; when the value of the logical delete field is-1, the query operation is executed, and sql is SELECT. FROM tb_user WHERE id=? AND logic_flag=1, so the query result is null.

5. Public fields are automatically filled in:

We know that when we insert or update, we do not set the property of the value, so it is either null or keep the original value in the data table. Sometimes we don't assign a value but don't want it to be empty. For example, the name attribute will be assigned "Lin Zhiling" by default when we insert it, and "Zhu Yin" will be assigned by default when updating, so we can fill it with public fields automatically.

1. Populate the fields with @ TableField comment marks

@ TableField (fill = FieldFill.INSERT_UPDATE) / / populate private String name when inserting and updating

2. Write common fields to populate the processor class:

Public class MyMetaObjectHandler extends MetaObjectHandler {@ Override public void insertFill (MetaObject metaObject) {Object fieldValue = getFieldValByName ("name", metaObject); / / get the field if to be populated (fieldValue = = null) {/ / if the field does not have a value setFieldValByName ("name", "Lin Chi Ling", metaObject) / / then set it to "Lin Zhiling"} @ Override public void updateFill (MetaObject metaObject) {Object fieldValue = getFieldValByName ("name", metaObject); / / get the field if (fieldValue = = null) {/ / if the field is not set to setFieldValByName ("name", "Zhu Yin", metaObject); / / set it to "Zhu Yin"}}

Note: this class inherits the MetaObjectHandler class and overrides the insertFill and updateFill methods, where you get the fields that need to be populated and the default populated values.

3. Configure in spring-dao.xml:

Note: as with configuration logic deletion, the custom class is first registered as bean, and then the bean is referenced in the global policy configuration.

4. Test:

@ Testpublic void testHandlerInsert () {User user = new User (); user.setGender (1); user.setAge (22); user.setLogicFlag (1); userDao.insert (user);}

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Note: you can see that although we have not assigned a value to name, we have automatically passed "Lin Zhiling" into it. It is also effective when updating, so the test code will not be posted here.

At this point, the study of "how to use mybatis-plus" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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