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This article introduces the knowledge of "what is the difference between springboot @ Repository and @ Mapper". Many people will encounter this dilemma in the operation of actual cases, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Today, when integrating mybatis with springboot, the annotation used on the mapper interface is the @ Repository annotation that I used to learn spring, but as soon as it is run, an error occurs.

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.

2020-11-19 20 o.s.b.d.LoggingFailureAnalysisReporter 2920.989 ERROR 15260-[restartedMain]

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APPLICATION FAILED TO START

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Description:

Field videoMapper in com.shenlei.service.impl.VideoServiceImpl required a bean of type 'com.shenlei.mapper.VideoMapper' that could not be found.

It was said that the bean of mapper could not be found, so I flipped through the notes I had learned from springboot and found that I wanted to use the annotation mappe. After adding it, it was all right.

So sum up the difference between @ Repository and @ Mapper

1. @ Repository

@ Repository is an annotation for Spring to declare a Bean. It is useless to use @ Repository alone. It can be understood that there is no point in liberating the note on the interface. In spring, write a @ Repository annotation on the mapper interface just to identify it. In order to really scan this interface, you must use @ MapperScannerConfigurer.

This configuration scans all interfaces under the com.shenlei.mapper package and creates their own dynamic proxy classes.

Integration with spring can be divided into three steps:

1. Bring the Mapper interface class corresponding to the java class into the total IOC container of spring.

2. Add the XML namespace corresponding to the Java class to the mapperRegistry in the Configuration class in Mybatis (used to manage the Mapper of Mybatis)

3. Use the IOC container in spring to expand FactoryBean to get the instance of Mapper. (the first step is to include spring as an interface.)

2. @ Mapper

@ Mapper is a comment that comes with mybatis itself. In the spring program, mybatis needs to find the corresponding mapper, generate dynamic proxy classes at compile time, and interact with the database. The @ Mapper annotation is needed.

But sometimes when we have a lot of mapper interfaces, we need to write a lot of @ Mappe annotations, which is very troublesome.

Annotate with @ MapperScan.

This automatically scans all mapper interfaces under the package path so that there is no need to add any comments to the interface.

3. Differences and similarities:

Both @ Mapper and @ Repository act on the dao layer interface to generate the proxy object bean, which is managed by the spring container.

For mybatis, you don't have to write mapper.xml files.

Differences:

1. @ Mapper does not need to configure the scan address and can be used separately. If you have multiple mapper files, you can add @ MapperScan ("the package where the mapper file resides") in the project startup class.

2. @ Repository cannot be used alone, otherwise an error will be reported. To use it, you must configure the scanning address (@ MapperScannerConfigurer).

4. Solve the red problem of injecting mapper when using @ mapper interface

If you use @ Mapper annotation alone in idea, idea will prompt you that bean cannot be found in @ Autowired, but it will not affect the operation. If you want to eliminate hot spots, you can use @ Mapper annotations with @ Repository annotations to eliminate hot spots.

In this way, the popularity can be eliminated.

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