add file management feature (#560)

### What problem does this PR solve?

### Type of change

- [x] Documentation Update

api/db/services/file2document_service.py

@@ -0,0 +1,66 @@
+#
+#  Copyright 2024 The InfiniFlow Authors. All Rights Reserved.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+from datetime import datetime
+
+from api.db.db_models import DB
+from api.db.db_models import File, Document, File2Document
+from api.db.services.common_service import CommonService
+from api.utils import current_timestamp, datetime_format
+
+
+class File2DocumentService(CommonService):
+    model = File2Document
+
+    @classmethod
+    @DB.connection_context()
+    def get_by_file_id(cls, file_id):
+        objs = cls.model.select().where(cls.model.file_id == file_id)
+        return objs
+
+    @classmethod
+    @DB.connection_context()
+    def get_by_document_id(cls, document_id):
+        objs = cls.model.select().where(cls.model.document_id == document_id)
+        return objs
+
+    @classmethod
+    @DB.connection_context()
+    def insert(cls, obj):
+        if not cls.save(**obj):
+            raise RuntimeError("Database error (File)!")
+        e, obj = cls.get_by_id(obj["id"])
+        if not e:
+            raise RuntimeError("Database error (File retrieval)!")
+        return obj
+
+    @classmethod
+    @DB.connection_context()
+    def delete_by_file_id(cls, file_id):
+        return cls.model.delete().where(cls.model.file_id == file_id).execute()
+
+    @classmethod
+    @DB.connection_context()
+    def delete_by_document_id(cls, doc_id):
+        return cls.model.delete().where(cls.model.document_id == doc_id).execute()
+
+    @classmethod
+    @DB.connection_context()
+    def update_by_file_id(cls, file_id, obj):
+        obj["update_time"] = current_timestamp()
+        obj["update_date"] = datetime_format(datetime.now())
+        num = cls.model.update(obj).where(cls.model.id == file_id).execute()
+        e, obj = cls.get_by_id(cls.model.id)
+        return obj