Only run the sqlite datetime hack on columns that are expecting a datetime object (#1270)

* Only run the SQLite datetime hack (#246) on columns that are expecting a datetime object
* Closes #1255

CTFd/utils/exports/__init__.py

@@ -14,9 +14,10 @@ from datafreeze.format.fjson import JSONEncoder, JSONSerializer
 from flask import current_app as app
 from flask_migrate import upgrade
 from sqlalchemy.exc import OperationalError, ProgrammingError
+from sqlalchemy.sql import sqltypes
 
 from CTFd.cache import cache
-from CTFd.models import db
+from CTFd.models import db, get_class_by_tablename
 from CTFd.utils import get_app_config, set_config
 from CTFd.utils.migrations import (
     create_database,
@@ -242,8 +243,20 @@ def import_ctf(backup, erase=True):
                     # This is a hack to get SQLite to properly accept datetime values from dataset
                     # See Issue #246
                     if sqlite:
+                        direct_table = get_class_by_tablename(table.name)
                         for k, v in entry.items():
                             if isinstance(v, six.string_types):
+                                # We only want to apply this hack to columns that are expecting a datetime object
+                                try:
+                                    is_dt_column = (
+                                        type(getattr(direct_table, k).type)
+                                        == sqltypes.DateTime
+                                    )
+                                except AttributeError:
+                                    is_dt_column = False
+
+                                # If the table is expecting a datetime, we should check if the string is one and convert it
+                                if is_dt_column:
                                     match = re.match(
                                         r"\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d", v
                                     )