Fix: AttachmentMapping과 FileAttachment 관계 재정의

두 관계 변경
- 기존: 다대일 관계 (일:FileAttachment, 다: AttachmentMapping)
- 변경: 일대일 관계

연관관계 주인 변경
- 기존: FileAttachment
- 변경: AttachmentMapping

Author: namgigun

src/main/java/com/back/domain/file/entity/AttachmentMapping.java

@@ -9,8 +9,7 @@
 @Getter
 @NoArgsConstructor
 public class AttachmentMapping extends BaseEntity {
-    @ManyToOne(fetch = FetchType.LAZY)
-    @JoinColumn(name = "attachment_id")
+    @OneToOne(fetch = FetchType.LAZY, mappedBy = "attachmentMapping", cascade = CascadeType.ALL, orphanRemoval = true)
     private FileAttachment fileAttachment;
 
     @Enumerated(EnumType.STRING)

src/main/java/com/back/domain/file/entity/FileAttachment.java

@@ -29,8 +29,9 @@ public class FileAttachment extends BaseEntity {
     @JoinColumn(name = "uploaded_by")
     private User user;
 
-    @OneToMany(mappedBy = "fileAttachment", cascade = CascadeType.ALL, orphanRemoval = true)
-    private List<AttachmentMapping> attachmentMappings = new ArrayList<>();
+    @OneToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "attachmentMapping_id")
+    private AttachmentMapping attachmentMapping;
 
     public FileAttachment(
             String storedName,