Thanks!! But the nodes are empty by using this method, and I checked the chromadb by retrieving, they are not empty. Here is my code:
# load db
db = chromadb.PersistentClient(path=db_path1)
chroma_collection = db.get_or_create_collection("quickstart")
vector_store = ChromaVectorStore(chroma_collection=chroma_collection)
index = VectorStoreIndex.from_vector_store(vector_store, service_context=ServiceContextModel()())
# load db_final
db_final = chromadb.PersistentClient(path=db_path2)
chroma_collection_final = db_final.get_or_create_collection("quickstart")
vector_store_final = ChromaVectorStore(chroma_collection=chroma_collection_final)
index_final = VectorStoreIndex.from_vector_store(vector_store_final, service_context=ServiceContextModel()())
nodes = index.docstore.docs
for node in nodes:
index_final.insert(node)