так правильнее

src/main/java/com/labwork1/app/student/controller/OrderMvcController.java

@@ -1,5 +1,6 @@
 package com.labwork1.app.student.controller;
 
+import com.labwork1.app.student.model.SessionExtension;
 import com.labwork1.app.student.service.CustomerService;
 import com.labwork1.app.student.service.OrderService;
 import com.labwork1.app.student.service.SessionService;

src/main/java/com/labwork1/app/student/controller/SessionDto.java

@@ -1,6 +1,7 @@
 package com.labwork1.app.student.controller;
 
 import com.labwork1.app.student.model.Session;
+import com.labwork1.app.student.model.SessionExtension;
 import org.springframework.format.annotation.DateTimeFormat;
 
 import java.time.LocalDateTime;
@@ -17,7 +18,7 @@ public class SessionDto {
     public SessionDto() {
     }
 
-    public SessionDto(Session session) {
+    public SessionDto(SessionExtension session) {
         this.id = session.getId();
         this.price = session.getPrice();
         this.timestamp = session.getTimestamp();
@@ -28,6 +29,16 @@ public class SessionDto {
         } else this.cinema = null;
     }
 
+    public SessionDto(Session session) {
+        this.id = session.getId();
+        this.price = session.getPrice();
+        this.timestamp = session.getTimestamp();
+        this.maxCount = session.getMaxCount();
+        if (session.getCinema() != null) {
+            this.cinema = new CinemaDto(session.getCinema());
+        } else this.cinema = null;
+    }
+
     public CinemaDto getCinema() {
         return cinema;
     }

src/main/java/com/labwork1/app/student/model/Session.java

@@ -14,24 +14,22 @@ import java.util.Objects;
 public class Session {
     @Id
     @GeneratedValue(strategy = GenerationType.AUTO)
-    private Long id;
+    protected Long id;
     @NotNull(message = "price can't be null or empty")
-    private Double price;
+    protected Double price;
     @NotNull(message = "timestamp can't be null or empty")
     @Column
     @Temporal(TemporalType.TIMESTAMP)
     @DateTimeFormat(pattern = "yyyy-MM-dd'T'HH:mm")
-    private LocalDateTime timestamp;
+    protected LocalDateTime timestamp;
     @OneToMany(mappedBy = "session", fetch = FetchType.EAGER)
     private List<OrderSession> orders;
     @ManyToOne(fetch = FetchType.EAGER)
     @JoinColumn(name = "cinema_fk")
-    private Cinema cinema;
+    protected Cinema cinema;
     @NotNull(message = "maxCount can't be null or empty")
     @Column
-    private Integer maxCount;
+    protected Integer maxCount;
-    @Transient
-    private Long capacity;
 
     public Session() {
     }
@@ -46,14 +44,13 @@ public class Session {
         this.maxCount = maxCount;
     }
 
-    public Session(Session session, Long capacity) {
+    public Session(Session session) {
         this.id = session.getId();
         this.price = session.getPrice();
         this.timestamp = session.getTimestamp();
         this.orders = session.getOrders();
         this.cinema = session.getCinema();
         this.maxCount = session.getMaxCount();
-        this.capacity = capacity;
     }
 
     public Cinema getCinema() {
@@ -98,7 +95,6 @@ public class Session {
                 "id=" + id +
                 ", price='" + price + '\'' +
                 ", timestamp='" + timestamp.toString() + '\'' +
-                ", capacity='" + capacity + '\'' +
                 ", maxCount='" + maxCount.toString() + '\'' +
                 ", cinema='" + cinema.toString() + '\'' +
                 '}';
@@ -139,12 +135,4 @@ public class Session {
     public List<OrderSession> getOrders() {
         return orders;
     }
-
-    public Long getCapacity() {
-        return capacity;
-    }
-
-    public void setCapacity(Long capacity) {
-        this.capacity = capacity;
-    }
 }

src/main/java/com/labwork1/app/student/model/SessionExtension.java

@@ -0,0 +1,17 @@
+package com.labwork1.app.student.model;
+
+public class SessionExtension extends Session {
+    private Long capacity;
+    public SessionExtension(Session session, Long capacity) {
+        super(session);
+        this.capacity = capacity;
+    }
+
+    public Long getCapacity() {
+        return capacity;
+    }
+
+    public void setCapacity(Long capacity) {
+        this.capacity = capacity;
+    }
+}

src/main/java/com/labwork1/app/student/repository/SessionRepository.java

@@ -1,6 +1,7 @@
 package com.labwork1.app.student.repository;
 
 import com.labwork1.app.student.model.Session;
+import com.labwork1.app.student.model.SessionExtension;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.query.Param;
@@ -11,13 +12,13 @@ import java.util.Optional;
 public interface SessionRepository extends JpaRepository<Session, Long> {
     @Query("Select sum(os.count) from OrderSession os where os.session.id = :sessionId")
     Optional<Integer> getCapacity(@Param("sessionId") Long sessionId);
-    @Query("Select new com.labwork1.app.student.model.Session(s, sum(os.count)) from Session s " +
+    @Query("Select new com.labwork1.app.student.model.SessionExtension(s, sum(os.count)) from Session s " +
             "left join OrderSession os on s.id = os.session.id " +
             "group by s")
-    List<Session> getSessionsWithCapacity();
+    List<SessionExtension> getSessionsWithCapacity();
-    @Query("Select new com.labwork1.app.student.model.Session(s, sum(os.count)) from Session s " +
+    @Query("Select new com.labwork1.app.student.model.SessionExtension(s, sum(os.count)) from Session s " +
             "left join OrderSession os on s.id = os.session.id " +
             "where s.id = :sessionId " +
             "group by s")
-    Optional<Session> getSessionWithCapacity(@Param("sessionId") Long sessionId);
+    Optional<SessionExtension> getSessionWithCapacity(@Param("sessionId") Long sessionId);
 }

src/main/java/com/labwork1/app/student/service/SessionService.java

@@ -2,6 +2,7 @@ package com.labwork1.app.student.service;
 
 import com.labwork1.app.student.model.Cinema;
 import com.labwork1.app.student.model.Session;
+import com.labwork1.app.student.model.SessionExtension;
 import com.labwork1.app.student.repository.SessionRepository;
 import com.labwork1.app.util.validation.ValidatorUtil;
 import org.springframework.stereotype.Service;
@@ -33,13 +34,13 @@ public class SessionService {
     }
 
     @Transactional(readOnly = true)
-    public Session findSession(Long id) {
+    public SessionExtension findSession(Long id) {
         return sessionRepository.getSessionWithCapacity(id)
                 .orElseThrow(() -> new SessionNotFoundException(id));
     }
 
     @Transactional(readOnly = true)
-    public List<Session> findAllSessions() {
+    public List<SessionExtension> findAllSessions() {
         return sessionRepository.getSessionsWithCapacity();
     }
 

src/test/java/com/labwork1/app/JpaCustomerTests.java

@@ -9,7 +9,7 @@ import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
 
-import java.sql.Timestamp;
+import java.time.LocalDateTime;
 import java.util.List;
 
 @SpringBootTest
@@ -36,9 +36,9 @@ public class JpaCustomerTests {
 
         // 2 сеанса
         final Session session1 = sessionService.addSession(300.0,
-                new Timestamp(System.currentTimeMillis()), cinema1.getId(), 10);
+                LocalDateTime.now(), cinema1.getId(), 10);
         final Session session2 = sessionService.addSession( 200.0,
-                new Timestamp(System.currentTimeMillis()), cinema1.getId(), 10);
+                LocalDateTime.now(), cinema1.getId(), 10);
 
         // проверка 2 сеанса у 1 кино
         Assertions.assertEquals(cinemaService
@@ -67,7 +67,7 @@ public class JpaCustomerTests {
         // у заказа 2 сеанса
         orderService.addSession(order2.getId(), session1.getId(), 2);
 
-        List<Session> result = sessionService.findAllSessions();
+        List<SessionExtension> result = sessionService.findAllSessions();
 
         Assertions.assertEquals(sessionService.getCapacity(session1.getId()), 2);
 
@@ -96,7 +96,7 @@ public class JpaCustomerTests {
         // у заказа 1 сеанс
         // 3 сеанса всего
         final Session session3 = sessionService.addSession(300.0,
-                new Timestamp(System.currentTimeMillis()), cinema2.getId(), 10);
+                LocalDateTime.now(), cinema2.getId(), 10);
         // удалили заказ2, у которого был сеанс1
         orderService.deleteOrder(order2.getId());
         Assertions.assertEquals(orderService.findAllOrders().size(), 0);