모임 참여 기능 구현

backend/src/main/java/mouda/backend/moim/controller/MoimController.java

@@ -16,6 +16,7 @@
 import mouda.backend.common.RestResponse;
 import mouda.backend.moim.domain.Moim;
 import mouda.backend.moim.dto.request.MoimCreateRequest;
+import mouda.backend.moim.dto.request.MoimJoinRequest;
 import mouda.backend.moim.dto.response.MoimDetailsFindResponse;
 import mouda.backend.moim.dto.response.MoimFindAllResponses;
 import mouda.backend.moim.service.MoimService;
@@ -55,6 +56,16 @@ public ResponseEntity<RestResponse<MoimDetailsFindResponse>> findMoimDetails(@Pa
 		return ResponseEntity.ok().body(new RestResponse<>(moimService.findMoimDetails(moimId)));
 	}
 
+	@Operation(summary = "모임 참여", description = "모임에 참여한다.")
+	@ApiResponses({
+		@ApiResponse(responseCode = "200", description = "모임 참여 성공!")
+	})
+	@PostMapping("/join")
+	public ResponseEntity<RestResponse<Void>> joinMoim(@RequestBody MoimJoinRequest moimJoinRequest) {
+		moimService.joinMoim(moimJoinRequest);
+		return ResponseEntity.ok().build();
+	}
+
 	@Operation(summary = "모임 삭제", description = "해당하는 id의 모임을 삭제한다.")
 	@ApiResponses({
 		@ApiResponse(responseCode = "200", description = "모임 삭제 성공!"),

backend/src/main/java/mouda/backend/moim/domain/Moim.java

@@ -37,4 +37,11 @@ public class Moim {
 	private String authorNickname;
 
 	private String description;
+
+	public void join() {
+		if (currentPeople + 1 > maxPeople) {
+			throw new IllegalArgumentException();
+		}
+		currentPeople++;
+	}
 }

backend/src/main/java/mouda/backend/moim/dto/request/MoimJoinRequest.java

@@ -0,0 +1,6 @@
+package mouda.backend.moim.dto.request;
+
+public record MoimJoinRequest(
+	Long moimId
+) {
+}

backend/src/main/java/mouda/backend/moim/service/MoimService.java

@@ -8,6 +8,7 @@
 import lombok.RequiredArgsConstructor;
 import mouda.backend.moim.domain.Moim;
 import mouda.backend.moim.dto.request.MoimCreateRequest;
+import mouda.backend.moim.dto.request.MoimJoinRequest;
 import mouda.backend.moim.dto.response.MoimDetailsFindResponse;
 import mouda.backend.moim.dto.response.MoimFindAllResponse;
 import mouda.backend.moim.dto.response.MoimFindAllResponses;
@@ -42,6 +43,12 @@ public MoimDetailsFindResponse findMoimDetails(long id) {
 		return MoimDetailsFindResponse.toResponse(moim);
 	}
 
+	public void joinMoim(MoimJoinRequest moimJoinRequest) {
+		Moim moim = moimRepository.findById(moimJoinRequest.moimId())
+			.orElseThrow(() -> new IllegalArgumentException("모임이 존재하지 않습니다."));
+		moim.join();
+	}
+
 	public void deleteMoim(long id) {
 		Moim moim = moimRepository.findById(id)
 			.orElseThrow(IllegalArgumentException::new);

backend/src/test/java/mouda/backend/moim/service/MoimServiceTest.java

@@ -15,6 +15,7 @@
 import mouda.backend.config.DatabaseCleaner;
 import mouda.backend.moim.domain.Moim;
 import mouda.backend.moim.dto.request.MoimCreateRequest;
+import mouda.backend.moim.dto.request.MoimJoinRequest;
 import mouda.backend.moim.dto.response.MoimDetailsFindResponse;
 import mouda.backend.moim.dto.response.MoimFindAllResponses;
 import mouda.backend.moim.repository.MoimRepository;
@@ -77,6 +78,22 @@ void findMoimDetails() {
 		assertThat(moimDetails.authorNickname()).isEqualTo("안나");
 	}
 
+	@DisplayName("모임에 참여한다.")
+	@Test
+	void joinMoim() {
+		MoimCreateRequest moimCreateRequest = new MoimCreateRequest(
+			"title", LocalDate.now(), LocalTime.now(), "place",
+			10, "안나", "설명"
+		);
+		moimService.createMoim(moimCreateRequest);
+
+		MoimJoinRequest moimJoinRequest = new MoimJoinRequest(1L);
+		moimService.joinMoim(moimJoinRequest);
+
+		MoimDetailsFindResponse moimDetails = moimService.findMoimDetails(1L);
+		assertThat(moimDetails.currentPeople()).isEqualTo(1);
+	}
+
 	@DisplayName("모임을 삭제한다.")
 	@Test
 	void deleteMoim() {