What is a ChromaDB collection and how do you create, list, get, and delete collections?

A collection is ChromaDB's primary organisational unit -analogous to a table in SQL or an index in a search engine. Each collection stores documents, their embeddings, IDs, and optional metadata. All items in a collection share the same embedding function and distance metric.

import chromadb

client = chromadb.PersistentClient(path="./chroma_db")

# CREATE a collection
collection = client.create_collection(
    name="research_papers",
    metadata={"hnsw:space": "cosine"},
    # embedding_function defaults to all-MiniLM-L6-v2
)

# GET an existing collection (raises error if not found)
collection = client.get_collection("research_papers")

# GET or CREATE - idempotent, safe to call on every startup
collection = client.get_or_create_collection(
    name="research_papers",
    metadata={"hnsw:space": "cosine"},
)

# LIST all collections
collections = client.list_collections()
for col in collections:
    print(col.name)  # prints collection names

# COUNT documents in a collection
print(collection.count())  # number of items stored

# DELETE a collection and all its data
client.delete_collection("research_papers")

# MODIFY collection name or metadata
collection.modify(
    name="arxiv_papers",
    metadata={"hnsw:space": "cosine", "description": "arXiv CS papers"},
)