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This article mainly introduces "the distinguishing way that Mybatis returns One and List". In daily operation, I believe that many people have doubts about the distinguishing way that Mybatis returns One and List. The editor consulted all kinds of data and sorted out a simple and easy-to-use method of operation. I hope it will be helpful to answer the doubt that "Mybatis returns One and List". Next, please follow the editor to study!

Return an object

Official website example: t selectOne (String statement)

Results: it may be null.

Note: when returning an object, a non-check exception TooManyResultsException eg is thrown if the database query result exceeds a record,Mybatis. : org.apache.ibatis.exceptions.TooManyResultsException: Expected one result (or null) to be returned by selectOne (), but found: 2 proves that there are two queries

Returns a List

Official website example: List selectList (String statement)

Result: if there is no return value, it will be an empty list, and there will be no null, so there is no need to determine the null value when using it, just loop it.

The official website explains the definition of interface:

The difference between selectOne and selectList is only in that selectOne must return exactly one object or null (none). If any more than one, an exception will be thrown. If you don't' know how many objects are expected, use selectList. If you want to check for the existence of an object, you're better off returning a count (0 or 1). The selectMap is a special case in that it is designed to convert a list of results into a Map based on one of the properties in the resulting objects. Because not all statements require a parameter, these methods are overloaded with versions that do not require the parameter object. The value returned by the insert, update and delete methods indicate the number of rows affected by the statement.

T selectOne (String statement) List selectList (String statement) Map selectMap (String statement, String mapKey) int insert (String statement) int update (String statement) int delete (String statement) ends the study of "how Mybatis returns One and List", hoping to solve everyone's 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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