In Spring Data JPA, when you define a derived query method like List<Restaurant> findByAddress(String addr) or a custom query method, you're instructing Spring Data JPA to automatically generate the implementation at runtime, based on the method name and parameter or based on custom JPQL.

Steps followed by Spring Data behind the scenes:

1. It parses the Method Name or custom query

   • findBy → indicates a query method.

   • Address → refers to a field named address in your Restaurant entity.

   • Constructs a query similar to:

     select r from Restaurant r where r.address = :addr
     
     

2. Binding the Parameter

   • Spring binds the method parameter addr to the named parameter :addr in the generated query.

3. Creating a Proxy at Runtime

   • Spring Data creates a proxy implementation of your repository interface using JDK dynamic proxies or CGLIB.
   • It registers this proxy as a Spring bean.
   • When you call findByAddress(...), Spring intercepts the call and runs the generated query.

4. Query Execution

   • Spring delegates the query to EntityManager (under the cover), which executes it via JPQL or SQL and returns the result.