Improve existing data check in 'export'

code/database/export.py

@@ -1,3 +1,4 @@
+from app.models import Annual_Data, Glacier, User
 from database.constants import DB_NAME, DB_PW, DB_USER
 from pandas import DataFrame, read_csv
 from sqlalchemy import create_engine, engine
@@ -25,8 +26,10 @@ def create_dataframes() -> DataFrame:
 
 
 def insert_data(df_list, conn):
-    if conn.table_names() is not None:
-        return
+    models = [Glacier, Annual_Data, User]
+    for model in models:
+        if model.query.first() is not None:
+            return
     for key, value in df_list.items():
         value.to_sql(key, con=conn, index=False, if_exists="append")