Using Agent to query Hydrus

You should have hydrus up and running. For instructions on how to start a hydrus server, checkout the quick start guide. To follow along you also need to have git and python3 installed.

hydra-python-agent or Agent is the smart Hydra client implemented in Python. The Agent is a smart client which is generic and automated that can establish resilient connected data networks leveraging knowledge graph.

hydra-python-agent exposes multiple convenient interfaces:

• A Python package - To make communication with a Hydra API easier in the software.
• Natural-language-like command line tool - This is a GET only implementation for now. It is in development.

Some of the important features of hydra-python-agent are:

1. It provides a seamless client that can be used to communicate with Hydra APIs.
2. It caches metadata from the Hydra server it connects to, to allow querying on the client-side.
3. It maintains a synchronization mechanism which makes sure cached resources are consistent.
4. It allows the graph to be queried using OpenCypher.

To use agent as a package in REPL:

1. Clone the repository by running this command in the terminal: git clone https://github.com/HTTP-APIs/hydra-python-agent.git.
2. Navigate into the repository by running: cd hydra-python-agent
3. Create a new virtual environment named agent: python3 -m venv agent.
4. Activate this virtual environment: source agent/bin/activate.
5. Install the necessary package: pip install -r requirements.txt. After this run: python3 setup.py install.
6. Start the redis server: docker run -p 6379:6379 -it --rm redislabs/redisgraph:2.0-edge. The agent uses redis to cache the meta data to make query faster.
7. Start the python3 REPL by typing python3 and pressing enter. You should see something like this:
8. In the REPL, import Agent:

from hydra_agent.agent import Agent

9. Connect Agent to hydrus by passing in the URL. The Agent is the factory class that returns the instance of the agent. All the CRUD operations can be invoked on this instance.

agent = Agent("http://localhost:8080/serverapi") # serverapi is the name of the API.

10. Once connected, we can now make CRUD operations.

Making CRUD Operations on Classes

To GET an existing resource make a GET request to:

agent.get("http://localhost:8080/serverapi/<ResourceType>/<Resource-ID>")
agent.get("http://localhost:8080/serverapi/<CollectionType>/")
agent.get("http://localhost:8080/serverapi/<CollectionType>/<Collection-ID>")

You should see the response.

To add a resource make a PUT request with the resource as the second parameter:

new_resource = {
    "@type": "Drone",
    "DroneState": {
        "@type": "State",
        "Battery": "50%",
        "Direction": "N",
        "Position": "50.34",
        "SensorStatus": "Active",
        "Speed": "100"
    },
    "MaxSpeed": "500",
    "Sensor": "Active",
    "model": "Drone_1",
    "name": "Drone1"
}
agent.put("http://localhost:8080/serverapi/Drone/", new_resource)

To update the resource Agent exposes the POST interface:

existing_resource["name"] = "Updated Name"
agent.post("http://localhost:8080/serverapi/<ResourceType>/<Resource-ID>", existing_resource)

To delete an existing resource, use the delete method:

agent.delete("http://localhost:8080/serverapi/<ResourceType>/<Resource-ID>")

Making CRUD Operations on Collections

To add members in the collection:

request_body = {
    "@type": "<CollectionType>",
    "members": [
        {
            "@id": "<ResourceID>",
            "@type": "<ResourceType>"
        },
        {
            "@id": "<ResourceID>",
            "@type": "<ResourceType>"
        },
    ]
}
agent.put("http://localhost:8080/serverapi/<CollectionType>", request_body)

NOTE: \<ResourceType> can be different in given request body.

TO GET members of specific Collection:

agent.get("http://localhost:8080/serverapi/<CollectionType>/<CollectionID>")

TO DELETE members of specific Collection:

agent.delete("http://localhost:8080/serverapi/<CollectionType>/<CollectionID>")

More than that, Agent class extends Session from https://2.python-requests.org/en/master/api/#request-sessions, so all methods like auth, cookies, headers and so on can also be used.

In this Tutorial you learnt about:

• smart clients
• hydra-python-agent
• Making CRUD operations using hydra-python-agent on classes
• Making CRUD operations using hydra-python-agent on Collections