How to addDocument with metadata tag with Langchain Milvus

Hi guys, i’m working my side projct and now i’m using Milvus and zilliz as vector database.
The problem is when i read and follow the doc about using
Milvus.addDocument(…) to add document object to zilliz database → it works but in the dynamic Field. I don’t see any metadata tag is being added.
can any one have experience in this ? Please help. thank you in advance