修复可以关注同一个话题的问题

src/main/java/cn/meteor/beyondclouds/modules/topic/enums/TopicErrorCode.java

@@ -12,7 +12,8 @@ public enum TopicErrorCode implements IErrorCode {
      * 话题已存在
      */
     TOPIC_EXISTS(3001, "该话题已存在"),
-    TOPIC_NOT_EXISTS(3002, "该话题不存在");
+    TOPIC_NOT_EXISTS(3002, "该话题不存在"),
+    AlREADY_FOLLOWED(3003, "已关注过该话题");
 
     TopicErrorCode(long code, String msg) {
         this.code = code;

src/main/java/cn/meteor/beyondclouds/modules/topic/service/impl/TopicServiceImpl.java

@@ -89,7 +89,16 @@ public class TopicServiceImpl extends ServiceImpl<TopicMapper, Topic> implements
             throw new TopicServiceException(TopicErrorCode.TOPIC_NOT_EXISTS);
         }
 
-        //3. 关注话题
+        //3. 判断用户是否已经关注该话题
+        QueryWrapper<TopicFollow> topicFollowQueryWrapper = new QueryWrapper<>();
+        topicFollowQueryWrapper.eq("user_id", userId);
+        topicFollowQueryWrapper.eq("topic", topicId);
+
+        if (null != topicFollowService.getOne(topicFollowQueryWrapper)) {
+            throw new TopicServiceException(TopicErrorCode.AlREADY_FOLLOWED);
+        }
+
+        //4. 关注话题
         TopicFollow topicFollow = new TopicFollow();
         topicFollow.setTopicId(topicId);
         topicFollow.setUserId(userId);