Add service code

src/main/java/com/gmu/bookshare/persistence/ShareUserRepository.java

@@ -3,6 +3,9 @@ package com.gmu.bookshare.persistence;
 import com.gmu.bookshare.entity.ShareUser;
 import org.springframework.data.repository.CrudRepository;
 
+import java.util.List;
+
 public interface ShareUserRepository extends CrudRepository<ShareUser, Long> {
 
+    List<ShareUser> findByEmail(String s);
 }

src/main/java/com/gmu/bookshare/service/ShareUserService.java

 package com.gmu.bookshare.service;
 
+import com.gmu.bookshare.entity.ShareUser;
 import com.gmu.bookshare.persistence.ShareUserRepository;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Service;
 
+import java.util.List;
+
 @Service
 public class ShareUserService {
 
@@ -13,4 +16,14 @@ public class ShareUserService {
     public ShareUserService(ShareUserRepository shareUserRepository) {
         this.shareUserRepository = shareUserRepository;
     }
+
+    public ShareUser addShareUser(ShareUser user) {
+        List<ShareUser> userList = shareUserRepository.findByEmail(user.getEmail());
+        if (userList.size() > 0) {
+            return userList.get(0);
+        } else {
+            shareUserRepository.save(user);
+            return user;
+        }
+    }
 }