Adding a metadata to Mongodb vector database

Hello,

I am using Mongodb Vector database with LangChain. I would like to add a metadata to each documents
and use the metadata to filter the results.
Can someone guide me?

loader = WebBaseLoader(
            [ " http://mongodb.com  "
            
            ]
            )

        data = loader.load()
        text_splitter = RecursiveCharacterTextSplitter(chunk_size=4000, chunk_overlap=500)
        docs = text_splitter.split_documents(data)
        metadata = {"user-id": "your-user-id"}  
        # Add Metadata to all docs here 
        client = MongoClient(self.config.mongodb_uri)
        MONGODB_COLLECTION = client[self.config.vector_db_name][self.config.collection_name]
        MongoDBAtlasVectorSearch.from_documents(
            documents=docs,
            embedding=OpenAIEmbeddings(disallowed_special=()),
            collection=MONGODB_COLLECTION,
            index_name=self.config.search_index_name,
            metadata=metadata 
        )

And in retrieval

# Add pre-filter here.

 vector_search = MongoDBAtlasVectorSearch.from_connection_string(
            self.config.mongodb_uri,
            self.config.vector_db_name  + "." + self.config.collection_name,
            OpenAIEmbeddings(disallowed_special=()),
            index_name=self.config.search_index_name,
        )
        retriever = vector_search.as_retriever()

Thanks!
I am working with Langchain, and the resource you provided worked for filtering the results for retrieval.

Followup question is:

How do I populate the vector database with custom metadata field ?
This is how I am adding the metadata

text_splitter = RecursiveCharacterTextSplitter(chunk_size=1000, chunk_overlap=100)
docs = text_splitter.split_documents(data)

# Help me find a better way than iterating over all the documents
for i, doc in enumerate(docs): 
     doc.metadata["user_id"] = user_id

MongoDBAtlasVectorSearch.from_documents(
            documents=docs,
            embedding=OpenAIEmbeddings(disallowed_special=()),
            collection=MONGODB_COLLECTION,
            index_name=self.config.search_index_name,
        )

Now for the retriever