MyBatis is a semi-automatic mapping framework. It is called semi-automatic because it needs to manually match the provided POJO, SQL, and mapping relationship, while Hibernate only needs to provide the POJO and mapping relationship.
Dynamic SQL
Dynamic SQL is mainly used to solve the situation of uncertain query conditions: during the running of the program, query according to the query conditions submitted by the user. The submitted query conditions are different, and the executed SQL statements are different. If each possible situation is listed one by one, and all the conditions are permuted and combined, a large number of SQL statements will appear. At this time, dynamic SQL can be used to solve such problems. That is, the conditions are judged through various tags provided by MyBatis to realize dynamic splicing of SQL statements.
If
Requirement: We are now doing user inquiries, it is possible to bring a user name, and there may be no
When querying, give a value that does not give username to observe the result
where
trim
The role of replacement
Attributes
description
prefix
The prefix for splicing SQL statements
suffix
Suffix for splicing sql statement
prefixOverrides
Remove the keyword or character in front of the sql statement. The keyword or character is specified by the prefixOverrides attribute. If the attribute is specified as "AND", when the beginning of the sql statement is "AND", the trim tag will remove the "AND"
suffixOverrides
Remove the keywords or characters after the SQL statement, the keywords or characters are specified by the suffixOverrides attribute
choose、when、otherwise
When multiple query conditions appear at the same time, sort the priority If …elseif…else
Set
If a table has multiple fields, but I only need to update the fields that need to be updated to reduce network bandwidth
foreach
Case, we do batch delete or update Method one, in the form of an integer array
