Metamorph

The metamorph operation transforms an Actor run into the run of another Actor with a new input.

---

Transform Actor runs

Metamorph is a powerful operation that transforms an Actor run into the run of another Actor with a new input. This feature enables you to leverage existing Actors and create more efficient workflows.

Understand metamorph

The metamorph process involves several key steps. It stops the current Actor's Docker container, then starts a new container using a different Docker image. During this transition, all default storages are preserved. The new input is stored under the INPUT-METAMORPH-1 key in the default key-value store, ensuring seamless data transfer between Actor runs.

Benefits of metamorph

Metamorph offers several benefits for developers:

• Seamless transition between Actors without starting a new run
• Building new Actors on top of existing ones
• Providing users with an improved input structure and interface
• Maintaining transparency for end-users

These benefits make metamorph a valuable tool for creating complex, efficient workflows.

Implementation guidelines

To make your Actor compatible with metamorph, use Actor.getInput() instead of Actor.getValue(`INPUT`). This method fetches the input using the correct key (INPUT-METAMORPH-1) for metamorphed runs, ensuring proper data retrieval in transformed Actor runs.

Runtime limits

There's a limit to how many times you can metamorph a single run. Refer to the Actor runtime limits for more details.

Example

Let's walk through an example of using metamorph to create a hotel review scraper:

1. Create an Actor that accepts a hotel URL as input.

2. Use the apify/web-scraper Actor to scrape reviews.

3. Use the metamorph operation to transform into a run of apify/web-scraper.

JavaScript

Here's the JavaScript code to achieve this:

import { Actor } from 'apify';

await Actor.init();

// Get input of your Actor.
const { hotelUrl } = await Actor.getInput();

// Create input for apify/web-scraper
const newInput = {
    startUrls: [{ url: hotelUrl }],
    pageFunction: () => {
        // Here you pass the page function that
        // scrapes all the reviews ...
    },
    // ... and here would be all the additional
    // input parameters.
};

// Transform the Actor run to apify/web-scraper
// with the new input.
await Actor.metamorph('apify/web-scraper', newInput);

// The line here will never be reached, because the
// Actor run will be interrupted.
await Actor.exit();

Python

Here's the Python code to achieve this:

from apify import Actor

async def main():
    async with Actor:
        # Get input of your Actor
        actor_input = await Actor.get_input() or {}

        # Create input for apify/web-scraper
        new_input = {
            'startUrls': [{'url': actor_input['url']}],
            'pageFunction': """
                # Here you pass the page function that
                # scrapes all the reviews ...
            """,
            # ... and here would be all the additional input parameters
        }

        # Transform the Actor run to apify/web-scraper with the new input
        await Actor.metamorph('apify/web-scraper', new_input)

        # The line here will never be reached, because the Actor run will be interrupted
        Actor.log.info('This should not be printed')

By following these steps, you can create a powerful hotel review scraper that leverages the capabilities of existing Actors through the metamorph operation.