What is data persistence?

1. What is persistence ？

　　 In a narrow sense :“ Persistence ” It only means to save the domain object permanently to the database ;

　　 In a broad sense ,“ Persistence ” Including various operations related to database .

　　　　● preservation ： Permanently save the domain object to the database .

　　　　● to update ： Update the status of domain objects in the database .

　　　　● Delete ： Delete a domain object from the database .

　　　　● load ： According to the specific OID, Load a domain object from the database into memory .

　　　　● Inquire about ： According to specific query conditions , Load one or more domain objects that meet the query conditions from the database into the internal memory .

2． Why persistence ？

　　 Persistence technology encapsulates the details of data access , Provide object-oriented services for most business logic API.

　　　　● Through Persistence technology, you can reduce the number of times to access database data , Increase application execution speed ;

　　　　● High code reusability , Able to complete most database operations ;

　　　　● Loose coupling , Make persistence independent of the underlying database and the upper business logic implementation , When changing the database, you only need to modify the configuration file without modifying the code .