Database master-slave mode, how to read slave database data? (please attach code)

The database is set up in the master-slave mode. The master database is responsible for additions, deletions and modifications, and the slave database is responsible for reading. But how to implement the code for reading data from the slave database? What should we pay attention to? Please advise

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The database is set up in the master-slave mode. The master database is responsible for additions, deletions and modifications, and the slave database is responsible for reading. But how to implement the code for reading data from the slave database? What should we pay attention to? Please advise