I am using Milvus as document store with Haystack.

MilvusDocumentStore connection object called with:

@lru_cache
def get_vector_db():
    # Get document store from database
    return MilvusDocumentStore(
        connection_args={
            "uri": get_settings().milvus_db_path
        },  # Milvus Lite
        drop_old=True
    )

And the Haystack pipeline defined as below:

 file_type_router = FileTypeRouter(
        mime_types=[
            "text/plain"
        ]
    )
    # Converter plain text files to Document objects
    text_converter = TextFileToDocument()
    # Join Documents coming from different branches of a pipeline
    document_joiner = DocumentJoiner()
    # Clean the text of the documents
    document_cleaner = DocumentCleaner()
    # Split the documents into smaller documents
    document_splitter = DocumentSplitter(split_by="sentence", split_length=2)
    # Create embeddings from the Documents
    document_embedder = SentenceTransformersDocumentEmbedder(
        model="sentence-transformers/all-MiniLM-L6-v2"
    )
    # Write the documents to the DocumentStore
    document_writer = DocumentWriter(document_store, policy=DuplicatePolicy.NONE)

    # Build the Indexing pipeline
    preprocessing_pipeline = Pipeline()
    preprocessing_pipeline.add_component(
        name="file_type_router", instance=file_type_router
    )
    preprocessing_pipeline.add_component(name="text_converter", instance=text_converter)
    preprocessing_pipeline.add_component(
        name="document_joiner", instance=document_joiner
    )
    preprocessing_pipeline.add_component(
        name="document_cleaner", instance=document_cleaner
    )
    preprocessing_pipeline.add_component(
        name="document_splitter", instance=document_splitter
    )
    preprocessing_pipeline.add_component(
        name="document_embedder", instance=document_embedder
    )
    preprocessing_pipeline.add_component(
        name="document_writer", instance=document_writer
    )

    # Connect components
    preprocessing_pipeline.connect(
        "file_type_router.plain/text, "text_converter.sources"
    )
    preprocessing_pipeline.connect("text_converter", "document_joiner")
    preprocessing_pipeline.connect("document_joiner", "document_cleaner")
    preprocessing_pipeline.connect("document_cleaner", "document_splitter")
    preprocessing_pipeline.connect("document_splitter", "document_embedder")
    preprocessing_pipeline.connect("document_embedder", "duplicate_checker")
    preprocessing_pipeline.connect(
        "duplicate_checker.documents_to_index", "document_writer.documents"
    )

When I try to write to the db I get the following error:

    Failed to create collection: HaystackCollection error: <MilvusException: 
    (code=2000, message=Assert "!name_ids_.count(field_name)" at 
    /Users/zilliz/milvus-lite/thirdparty/milvus/internal/core/src/common/Schema.h:172
    => duplicated field name: segcore error)>
    ERROR:    Exception in ASGI application

Following the error with the debugger seems like there is an attempt to recreate the default database collection.