[Draft] Add Example ChromadbMemory in Extensions

[victordibia]

Why are these changes needed?

Shows an example of how to use the Memory interface to implement a just-in-time vector memory based on chromadb.

from autogen_core.memory import MemoryContent, MemoryMimeType
from autogen_agentchat.agents import AssistantAgent
from autogen_ext.models.openai import OpenAIChatCompletionClient
from autogen_agentchat.ui import Console
from autogen_ext.memory.chromadb import ChromaMemory, ChromaMemoryConfig, ChromaMemoryContent

async def main():
    # Initialize ChromaDB memory with custom config
    user_memory = ChromaMemory(
        name="user_preferences",
        config=ChromaMemoryConfig(
            collection_name="preferences",
            persistence_path="./chroma_db",  # Optional: persist to disk
            k=2,  # Return top 5 results
            score_threshold=0.4,  # Minimum similarity score
        )
    )

    # Add user preferences to memory
    await user_memory.add(
        MemoryContent(
            content="The weather should be in metric units",
            mime_type=MemoryMimeType.TEXT,
            metadata={"category": "preferences", "type": "units"}
        )
    )
    
    await user_memory.add(
        MemoryContent(
            content="Meal recipe must be vegan",
            mime_type=MemoryMimeType.TEXT,
            metadata={"category": "preferences", "type": "dietary"}
        )
    )

    async def get_weather(city: str, units: str = "imperial") -> str:
        if units == "imperial":
            return f"The weather in {city} is 73 °F and Sunny."
        elif units == "metric":
            return f"The weather in {city} is 23 °C and Sunny."
        else:
            return f"Sorry, I don't know the weather in {city}."

    # Create assistant agent with ChromaDB memory
    assistant_agent = AssistantAgent(
        name="assistant_agent",
        model_client=OpenAIChatCompletionClient(
            model="gpt-4o",
        ),
        tools=[get_weather],
        memory=[user_memory],
    )

    stream = assistant_agent.run_stream(task="What is the weather in New York?")
    await Console(stream)
 
    await user_memory.close()

# if __name__ == "__main__":
#     import asyncio
#     asyncio.run(main())

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov]

Codecov Report

Attention: Patch coverage is 75.73529% with 33 lines in your changes missing coverage. Please review.

Project coverage is 70.65%. Comparing base (a673957) to head (22dd6b0).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...ges/autogen-ext/src/autogen_ext/memory/chromadb.py	75.73%	33 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5308      +/-   ##
==========================================
+ Coverage   70.59%   70.65%   +0.05%     
==========================================
  Files         180      181       +1     
  Lines       11668    11804     +136     
==========================================
+ Hits         8237     8340     +103     
- Misses       3431     3464      +33     

Flag	Coverage Δ
unittests	70.65% <75.73%> (+0.05%)	⬆️

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