ASAP-451 익명 편지 생성 로직 및 DB 스키마 수정

- `send_letter.sender_id`를 nullable로 수정: 도메인, 엔터티, 매퍼 및 DDL 변경.
- 익명 편지 생성 팩토리 메서드 `createAnonymous` 추가.

Author: tlarbals824

Domain-Module/src/main/kotlin/com/asap/domain/letter/entity/SendLetter.kt

@@ -12,7 +12,7 @@ import java.time.LocalDateTime
 class SendLetter(
     id: DomainId,
     val content: LetterContent,
-    val senderId: DomainId,
+    val senderId: DomainId? = null,
     var receiverName: String,
     var letterCode: String?,
     var status: LetterStatus,
@@ -46,6 +46,27 @@ class SendLetter(
         ).also {
             it.registerEvent(SendLetterEvent.SendLetterCreatedEvent(it, draftId?.value))
         }
+
+        fun createAnonymous(
+            content: LetterContent,
+            receiverName: String,
+            letterCode: String?,
+            status: LetterStatus = LetterStatus.SENDING,
+            receiverId: DomainId? = null,
+            createdAt: LocalDateTime = LocalDateTime.now(),
+            updatedAt: LocalDateTime = LocalDateTime.now(),
+        ): SendLetter =
+            SendLetter(
+                id = DomainId.generate(),
+                content = content,
+                senderId = null,
+                receiverName = receiverName,
+                letterCode = letterCode,
+                status = status,
+                receiverId = receiverId,
+                createdAt = createdAt,
+                updatedAt = updatedAt,
+            )
     }
 
     fun isSameReceiver(receiver: () -> User): Boolean {

Infrastructure-Module/Persistence/src/main/kotlin/com/asap/persistence/jpa/letter/SendLetterMapper.kt

@@ -17,7 +17,7 @@ object SendLetterMapper {
                 ),
             receiverName = sendLetterEntity.receiverName,
             letterCode = sendLetterEntity.letterCode ?: "",
-            senderId = DomainId(sendLetterEntity.senderId),
+            senderId = sendLetterEntity.senderId?.let { DomainId(it) },
             receiverId = sendLetterEntity.receiverId?.let { DomainId(it) },
             status = sendLetterEntity.letterStatus,
             createdAt = sendLetterEntity.createdAt,
@@ -31,7 +31,7 @@ object SendLetterMapper {
             images = sendLetter.content.images,
             templateType = sendLetter.content.templateType,
             receiverName = sendLetter.receiverName,
-            senderId = sendLetter.senderId.value,
+            senderId = sendLetter.senderId?.value,
             letterCode = sendLetter.letterCode,
             receiverId = sendLetter.receiverId?.value,
             letterStatus = sendLetter.status,

Infrastructure-Module/Persistence/src/main/kotlin/com/asap/persistence/jpa/letter/entity/SendLetterEntity.kt

@@ -26,7 +26,7 @@ class SendLetterEntity(
     content: String,
     images: List<String>,
     templateType: Int,
-    senderId: String,
+    senderId: String?,
     letterCode: String?,
     receiverId: String?,
     letterStatus: LetterStatus,
@@ -49,17 +49,16 @@ class SendLetterEntity(
     var images: List<String> = images
     var templateType: Int = templateType
 
-    @Column(name = "sender_id", nullable = false)
-    var senderId: String = senderId
+    @Column(name = "sender_id")
+    var senderId: String? = senderId
 
     @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(
         name = "sender_id",
-        nullable = false,
         insertable = false,
         updatable = false,
     )
-    lateinit var sender: UserEntity
+    var sender: UserEntity? = null
 
     @Column(name = "receiver_id")
     var receiverId: String? = receiverId

Infrastructure-Module/Persistence/src/main/resources/db/V1_20__alter_send_letter_sender_id_to_nullable.sql

@@ -0,0 +1 @@
+ALTER TABLE send_letter MODIFY COLUMN sender_id VARCHAR(255) NULL;