projections: Spring Data JPA interface, record, nested and dynamic projections with the SQL they generate

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b5sejRr8s3kapmRY2g

projections/output/01-entity-vs-closed-vs-dto.txt

@@ -0,0 +1,11 @@
+# entity result: findByDepartmentName("Sales")
+select e1_0.id,e1_0.bio,e1_0.department_id,e1_0.email,e1_0.first_name,e1_0.last_name,e1_0.salary from employee e1_0 left join department d1_0 on d1_0.id=e1_0.department_id where d1_0.name=?
+columns selected: 7, entities now managed by the persistence context: 4
+
+# closed interface projection: findSummaryByDepartmentName("Sales")
+select e1_0.first_name,e1_0.last_name from employee e1_0 left join department d1_0 on d1_0.id=e1_0.department_id where d1_0.name=?
+columns selected: 2, entities now managed by the persistence context: 0
+
+# record DTO projection: findDtoByDepartmentName("Sales")
+select e1_0.first_name,e1_0.last_name from employee e1_0 left join department d1_0 on d1_0.id=e1_0.department_id where d1_0.name=?
+columns selected: 2, entities now managed by the persistence context: 0

projections/output/02-open-projection-trap.txt

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+# open projection: findFullNameByDepartmentName("Sales")  (getFullName uses @Value SpEL)
+select e1_0.id,e1_0.bio,e1_0.department_id,e1_0.email,e1_0.first_name,e1_0.last_name,e1_0.salary from employee e1_0 left join department d1_0 on d1_0.id=e1_0.department_id where d1_0.name=?
+columns selected: 7, entities now managed by the persistence context: 4
+getFullName() of first row: First1 Last1

projections/output/03-nested-projection.txt

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+# nested projection: asks for firstName and department.name only
+select e1_0.first_name,d1_0.id,d1_0.location,d1_0.name from employee e1_0 left join department d1_0 on d1_0.id=e1_0.department_id where d1_0.name=?
+columns selected: 4 (1 from employee + 3 from department), entities now managed: 1
+department name read from the projection: Sales
+extra statements after reading it: 0

projections/output/04-dynamic-projection.txt

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+# one repository method, three result shapes: findByDepartmentName("Sales", Class<T>)
+Employee         -> 4 rows, 7 columns: select e1_0.id,e1_0.bio,e1_0.department_id,e1_0.email,e1_0.first_name,e1_0.last_name,e1_0.salary
+EmployeeSummary  -> 4 rows, 2 columns: select e1_0.first_name,e1_0.last_name
+EmployeeDto      -> 4 rows, 2 columns: select e1_0.first_name,e1_0.last_name

projections/output/05-query-forms.txt

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+# @Query with aliases, declared as an interface projection
+select e1_0.first_name,e1_0.last_name from employee e1_0 where e1_0.salary>?
+rows: 6, first getFirstName(): First6
+
+# @Query with a constructor expression (select new ...DepartmentPay)
+select d1_0.name,count(e1_0.id),sum(e1_0.salary) from employee e1_0 join department d1_0 on d1_0.id=e1_0.department_id group by d1_0.name order by d1_0.name
+DepartmentPay[department=Engineering, headcount=4, totalSalary=218000.00]
+DepartmentPay[department=HR, headcount=4, totalSalary=226000.00]
+DepartmentPay[department=Sales, headcount=4, totalSalary=222000.00]
+
+# native query with column aliases equal to the getter names
+select first_name as firstName, last_name as lastName from employee where salary > ?
+rows: 6, first getFirstName(): First6

projections/output/06-pitfall-entity-query.txt

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+# @Query("select e from Employee e ...") declared as List<EmployeeSummary>
+select e1_0.id,e1_0.bio,e1_0.department_id,e1_0.email,e1_0.first_name,e1_0.last_name,e1_0.salary from employee e1_0 where e1_0.salary>?
+columns selected: 7, entities now managed: 6, rows: 6

projections/output/07-pitfall-missing-aliases.txt

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+# @Query("select e.firstName, e.lastName from Employee e ...") with NO aliases
+select e1_0.first_name,e1_0.last_name from employee e1_0 where e1_0.salary>?
+rows: 6
+getFirstName() of first row: null
+getLastName() of first row: null

projections/output/08-pitfall-unknown-property.txt

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+# dynamic projection onto an interface with getNickname(), which Employee does not have
+org.springframework.data.core.PropertyReferenceException
+No property 'nickname' found for type 'Employee'

projections/output/09-paging-and-proxy.txt

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+# Page<EmployeeSummary>, page size 2
+select e1_0.first_name,e1_0.last_name from employee e1_0 left join department d1_0 on d1_0.id=e1_0.department_id where d1_0.name=? fetch first ? rows only
+select count(*) from employee e1_0 left join department d1_0 on d1_0.id=e1_0.department_id where d1_0.name=?
+statements: 2, rows in page: 2, total elements: 4
+
+# what an interface projection really is at runtime
+is a java.lang.reflect.Proxy: true
+is an Employee: false

projections/output/10-entity-query-as-dto-rewrite.txt

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+# @Query("select e from Employee e ...") declared as List<EmployeeDto> (a record)
+select e1_0.first_name,e1_0.last_name from employee e1_0 where e1_0.salary>?
+columns selected: 2, entities now managed: 0, rows: 6

projections/output/11-default-method-fix.txt

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+# closed projection with a default method: findFullNameClosedByDepartmentName("Sales")
+select e1_0.first_name,e1_0.last_name from employee e1_0 left join department d1_0 on d1_0.id=e1_0.department_id where d1_0.name=?
+columns selected: 2, entities now managed by the persistence context: 0
+getFullName() of first row: First1 Last1