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This article is about how the MyBatis framework implements query statements through xml mapping files. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

What is the Mybatis framework?

MyBatis is an excellent persistence layer framework that supports customized SQL, stored procedures, and advanced mapping. MyBatis avoids almost all JDBC code and manually setting parameters and getting result sets. MyBatis can use simple XML or annotations to configure and map native information, mapping interfaces and Java's POJOs (Plain Ordinary Java Object, ordinary Java objects) to records in the database.

How to use it?

Pom file dependency

Org.mybatis.spring.boot mybatis-spring-boot-starter 2.1.3

Yml file configuration, which matches the mapping file under the resource/mapper/ path.

Mybatis: mapper-locations: classpath:mapper/*.xml

Bind persistence layer interfaces and entity objects in a xml file

The namespace attribute in the mapper tag specifies the project path of our persistence layer interface

ResultMap is the most powerful element of Mybatis. It can map complex data from queries (such as queries to data in several tables) to a result set.

The type attribute of the resultMap tag is the project path of the entity object we want to map, and id is the unique identity of the resultMap.

The result tag in resultMap is the binding between the entity and the database table field, where the property attribute is the attribute name of the entity object, column is the field name of the database, and jdbcType is the field type.

Sql programming of xml Mapping File

Query through entities as filter criteria

Select id, host_name, ip, user_name, pass_word, state, tag, gmt_created, gmt_modified from host and id = # {id} and host_name like CONCAT ('%', # {hostName},'%') and ip like CONCAT ('%' # {ip},'%') and user_name = # {userName} and pass_word = # {passWord} and state = # {state} and tag = # {tag} and gmt_created = # {gmtCreated} and gmt_modified = # {gmtModified} / if >

Id= "queryAll" is the abstract method name of the persistence layer interface

The resultMap= "HostMap" specifies the result set of the resultMap received by the query result.

Persistence layer interface binding

/ * * conditional query * * @ param host conditional query * @ return object list * / List queryAll (Host host)

Batch delete through primary key

Delete from host where id in # {id}

The prototype of the above sql statement is

Delete from host where id in (1, 2, 3)

Attribute understanding in foreach tags

The collection property is the received data source

Item is every element in the collection

Index: used to indicate the location of each iteration during the iteration

Open: indicates what the statement starts with

Separator: indicates what symbol is used as a delimiter for data during iteration

Close: indicates what to end with

Abstract method of persistence layer interface

/ * bulk delete hosts * * @ param hostIds host id array * @ return Integer * / Integer deleteHostByIds (@ Param ("hostIds") Long [] hostIds)

Batch addition

Insert into host_and_group (host_group_id, host_id) values (# {hostGroupId}, # {hostId})

Persistent layer interface method

/ * add multiple hosts to a host group * * @ param request * @ return Integer * / Integer addHostList (HostAndGroupRequest request)

I am an element encapsulated in an object, so if there are a batch of elements in this object, you can pass an object directly.

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