оно даже работает

demo/src/main/java/com/example/demo/controllers/PlayController.java

@@ -1,7 +1,9 @@
 package com.example.demo.controllers;
 
 import com.example.demo.core.config.Constants;
+import com.example.demo.dtos.CustomerDto;
 import com.example.demo.dtos.PlayDto;
+import com.example.demo.models.Customer;
 import com.example.demo.services.PlayService;
 import org.springframework.web.bind.annotation.*;
 
@@ -41,7 +43,12 @@ public class PlayController {
     }
 
     @PostMapping("/{id}/customers")
-    public boolean addCustomer(@PathVariable(name = "id") long id, long customerId){
+    public boolean addCustomer(@PathVariable(name = "id") long id, @RequestParam long customerId){
         return playService.addCustomer(id, customerId);
     }
+
+    @GetMapping("/{id}/customers")
+    public List<CustomerDto> getCustomers(@PathVariable(name = "id") long id){
+        return playService.findPlay(id).getCustomers().stream().map(CustomerDto::new).toList();
+    }
 }

demo/src/main/java/com/example/demo/dtos/GameDto.java

@@ -4,6 +4,7 @@ import com.example.demo.models.Game;
 import jakarta.validation.constraints.Min;
 import jakarta.validation.constraints.NotNull;
 
+import java.util.ArrayList;
 import java.util.List;
 
 public class GameDto {
@@ -23,6 +24,7 @@ public class GameDto {
     }
 
     public GameDto(Game game){
+        id = game.getId();
         name = game.getName();
         description = game.getDescription();
 
@@ -30,11 +32,17 @@ public class GameDto {
         if (customerExist != null){
             customer = new CustomerDto(customerExist);
         }
+        else {
+            customer = null;
+        }
 
         var playsExist = game.getPlays();
         if (playsExist != null && !playsExist.isEmpty()){
             plays = playsExist.stream().map(PlayDto::new).toList();
         }
+        else {
+            plays = new ArrayList<>();
+        }
     }
 
     public String getName() {

demo/src/main/java/com/example/demo/dtos/PlayDto.java

@@ -3,6 +3,7 @@ package com.example.demo.dtos;
 import com.example.demo.models.Play;
 import jakarta.validation.constraints.NotNull;
 
+import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
 
@@ -24,6 +25,7 @@ public class PlayDto {
     }
 
     public PlayDto(Play play){
+        id = play.getId();
         description = play.getDescription();
         date = play.getDate();
 
@@ -34,6 +36,14 @@ public class PlayDto {
         else {
             game = null;
         }
+
+        var existCustomers = play.getCustomers();
+        if (existCustomers != null && !existCustomers.isEmpty()){
+            customers = existCustomers.stream().map(CustomerDto::new).toList();
+        }
+        else {
+            customers = new ArrayList<>();
+        }
     }
 
     public String getDescription(){

demo/src/main/java/com/example/demo/models/Game.java

@@ -75,10 +75,6 @@ public class Game {
         this.customerId = customer.getId();
     }
 
-    public long getCustomerId() {
-        return customerId;
-    }
-
     public Set<Play> getPlays(){
         return plays;
     }

demo/src/main/java/com/example/demo/models/Play.java

@@ -85,4 +85,7 @@ public class Play {
     public void setCustomers(List<Customer> customers){
         this.customers = customers;
     }
+    public boolean addCustomer(Customer customer){
+        return customers.add(customer);
+    }
 }

demo/src/main/java/com/example/demo/services/GameService.java

@@ -31,18 +31,18 @@ public class GameService {
         if (customer == null){
             throw new IllegalArgumentException("customerId invalid");
         }
-        final Game Game = new Game(name, description, customer);
+        final Game game = new Game(name, description, customer);
-        em.persist(Game);
+        em.persist(game);
-        return Game;
+        return game;
     }
 
     @Transactional
     public Game findGame(Long id){
-        final Game Game = em.find(Game.class, id);
+        final Game game = em.find(Game.class, id);
-        if(Game==null){
+        if(game == null){
             throw new EntityNotFoundException(String.format("Game with id [%s] is not found", id));
         }
-        return Game;
+        return game;
     }
 
     @Transactional