Create a derivation with flowctl

Once you're familiar with creating a basic Data Flow, you can take things a step further and transform your data with derivations.

A derivation is a kind of Flow collection that results from the transformation of one or more other collections. This transformed stream of data keeps the order of the source data intact, and can then be materialized to an outside system or further transformed with another derivation. When you master derivations, you unlock the full flexibility and power of Flow.

Prerequisites

• A Flow account and access to the web app. If you don't have an account yet, go to the web app to register for free.

• An existing Flow collection. Typically, you create this through a capture in the Flow web application. If you need help, see the guide to create a Data Flow.

• A development environment to work with flowctl. Choose between:

  • GitPod, the cloud development environment integrated with Flow. GitPod comes ready for derivation writing, with stubbed out files and flowctl installed. You'll need a GitLab, GitHub, or BitBucket account to log in.

  • Your local development environment. Install flowctl locally

Get started with GitPod

You'll write your derivation using GitPod, a cloud development environment integrated in the Flow web app.

1. Navigate to the Collections page in Flow.

2. Click on the New Transformation button.

   The Derive A New Collection pop-up window appears.

3. In the Available Collections dropdown, select the collection you want to use as the source.

   For example, if your organization is acmeCo, you might choose the acmeCo/resources/anvils collection.

4. Set the transformation language to either SQL and TypeScript.

   SQL transformations can be a more approachable place to start if you're new to derivations. TypeScript transformations can provide more resiliency against failures through static type checking.

5. Give your derivation a name. From the dropdown, choose the name of your catalog prefix and append a unique name, for example acmeCo/resources/anvil-status.

6. Click Proceed to GitPod to create your development environment. Sign in with one of the available account types.

7. On the New Workspace screen, keep the Context URL option selected and click Continue.

   A GitPod development environment opens. A stubbed-out derivation with a transformation has already been created for you in the language you chose. Next, you'll locate and open the source files.

8. Each slash-delimited prefix of your derivation name has become a folder. Open the nested folders to find the flow.yaml file with the derivation specification.

   Following the example above, you'd open the folders called acmeCo, then resources to find the correct flow.yaml file.

   The file contains a placeholder collection specification and schema for the derivation.

   In the same folder, you'll also find supplementary TypeScript or SQL files you'll need for your transformation.

Continue with SQL

Continue with TypeScript

Authentication

When you first connect to GitPod, you will have already authenticated Flow, but if you leave GitPod opened for too long, you may have to reauthenticate Flow. To do this:

1. Go to the CLI-API tab of the web app and copy your access token.

2. Run flowctl auth token --token <paste-token-here> in the GitPod terminal.

Add a SQL derivation in GitPod

If you chose SQL as your transformation language, follow these steps.

Along with the derivation's flow.yaml you found in the previous steps, there are two other files:

• A lambda file. This is where you'll write your first SQL transformation. Its name follows the pattern derivation-name.lambda.source-collection-name.sql. Using the example above, it'd be called anvil-status.lambda.anvils.sql.

• A migrations file. Migrations allow you to leverage other features of the sqlite database that backs your derivation by creating tables, indices, views, and more. Its name follows the pattern derivation-name.migration.0.sql. Using the example above, it'd be called anvil-status.migration.0.sql.

1. Open the flow.yaml file for your derivation. It looks something like this:

   collections:
     acmeCo/resources/anvil-status:
       schema:
         properties:
           your_key:
             type: string
           required:
             - your_key
         type: object
       key:
         - /your_key
       derive:
         using:
           sqlite:
             migrations:
               - anvil-status.migration.0.sql
         transforms:
           - name: anvils
             source: acmeCo/resources/anvils
             shuffle: any
             lambda: anvil-status.lambda.anvils.sql

   Note the stubbed out schema and key.

2. Write the schema you'd like your derivation to conform to and specify its collection key. Keep in mind:

   • The source collection's schema.

   • The transformation required to get from the source schema to the new schema.

3. Give the transform a unique name (by default, it's the name of the source collection).

4. In the lambda file, write your SQL transformation.

Tip

For help writing your derivation, start with these examples:

• Continuous materialized view tutorial
• Acme Bank examples

The main derivations page includes many other examples and in-depth explanations of how derivations work.

5. If necessary, open the migration file and write your migration.

6. Preview the derivation locally.

   flowctl preview --source flow.yaml

7. If the preview output appears as expected, publish the derivation.

   flowctl catalog publish --source flow.yaml

The derivation you created is now live and ready for further use. You can access it from the web application and materialize it to a destination, just as you would any other Flow collection.

Add a TypeScript derivation in GitPod

If you chose TypeScript as your transformation language, follow these steps.

Along with the derivation's flow.yaml you found in the previous steps, there's another file for the TypeScript transformation. It follows the naming convention derivation-name.ts. Using the example above, it'd be called anvil-status.ts.

1. Open the flow.yaml file for your derivation. It looks something like this:

   collections:
     acmeCo/resources/anvil-status:
       schema:
         properties:
           your_key:
             type: string
           required:
             - your_key
         type: object
       key:
         - /your_key
       derive:
         using:
           typescript:
             module: anvil-status.ts
         transforms:
           - name: anvils
           source: acmeCo/resources/anvils
           shuffle: any

   Note the stubbed out schema and key.

2. Write the schema you'd like your derivation to conform to and specify the collection key. Keep in mind:

   • The source collection's schema.

   • The transformation required to get from the source schema to the new schema.

3. Give the transform a unique name (by default, it's the name of the source collection).

4. In the TypeScript file, write your transformation.

Tip

For help writing a TypeScript derivation, start with this example.

The main derivations page includes many other examples and in-depth explanations of how derivations work.

6. Preview the derivation locally.

   flowctl preview --source flow.yaml

7. If the preview output appears how you'd expect, publish the derivation.

   flowctl catalog publish --source flow.yaml

The derivation you created is now live and ready for further use. You can access it from the web application and materialize it to a destination, just as you would any other Flow collection.

Create a derivation locally

Creating a derivation locally is largely the same as using GitPod, but has some extra steps. Those extra steps are explained here, but you'll find more useful context in the sections above.

1. Authorize flowctl.

   1. Go to the CLI-API tab of the web app and copy your access token.

   2. Run flowctl auth token --token <paste-token-here> in your local environment.

2. Locate the source collection for your derivation.

   • Check the web app's Collections. All published entities to which you have access are listed and can be searched.

   • Run flowctl catalog list --collections. This command returns a complete list of collections to which you have access. You can refine by specifying a --prefix.

3. Pull the source collection locally using the full collection name.

   flowctl catalog pull-specs --name acmeCo/resources/anvils

   The source files are written to your current working directory.

4. Each slash-delimited prefix of your collection name has become a folder. Open the nested folders to find the flow.yaml file with the collection specification.

   Following the example above, you'd open the folders called acmeCo, then resources to find the correct flow.yaml file.

   The file contains the source collection specification and schema.

5. Add the derivation as a second collection in the flow.yaml file.

   1. Write the schema you'd like your derivation to conform to and specify the collection key. Reference the source collection's schema, and keep in mind the transformation required to get from the source schema to the new schema.

   2. Add the derive stanza. See examples for SQL and TypeScript above. Give your transform a a unique name.

6. Stub out the SQL or TypeScript files for your transform.

   flowctl generate --source flow.yaml

7. Locate the generated file, likely in the same subdirectory as the flow.yaml file you've been working in.

8. Write your transformation.

9. Preview the derivation locally.

flowctl preview --source flow.yaml

7. If the preview output appears how you'd expect, publish the derivation.

flowctl catalog publish --source flow.yaml

The derivation you created is now live and ready for further use. You can access it from the web application and materialize it to a destination, just as you would any other Flow collection.

Updating an existing derivation

Derivations are applied on a go-forward basis only.

If you would like to make an update to an existing derivation (for example, adding columns to the derived collection), you can add a new transform by changing the name of your existing transform to a new name, and at the same time updating your lambda or TypeScript module.

From the Flow's perspective, this is equivalent to deleting the old transform and adding a new one. This will backfill over the source collection again with the updated SQL statement.