# Create a Custom Extractor

As much as we'd like to support all the data sources out there, we'll need your help to get there. If you find a data source that Meltano doesn't support right now, it might be time to get your hands dirty.

We aim to make Meltano as thin as possible on top of the components it abstracts, so adding a new plugin should be straightforward.

# How to Create a Extractor

First things first, you'll need a data source to integrate: in this example, let's say we want to create a tap to fetch data from GitLab.

# Create the Plugin's Package

Meltano uses Singer taps and targets to extract and load data. For more details about the Singer specification, please visit https://github.com/singer-io/getting-started

pip3 install cookiecutter
cookiecutter gh:singer-io/singer-tap-template
> project_name: tap-gitlab-custom

# Add the Plugin to Your Meltano Project (--custom)

Now that your plugin is part of your Meltano project, you need to add your plugin configuration in the meltano.yml's plugin definition.

meltano add --custom extractor tap-gitlab-custom
...
> namespace: gitlab
> pip_url: -e tap-gitlab-custom
> executable: tap-gitlab-custom
> capabilities: catalog,discover,state

Meltano exposes each plugin configuration in the plugin definition, located in the meltano.yml file.

Looking at the tap-gitlab-custom definition, we should see the following (notice the settings section is missing):

meltano.yml

plugins:
  extractors:
    - capabilities:
      - catalog
      - discover
      - state
      executable: tap-gitlab-custom
      name: tap-gitlab-custom
      namespace: gitlab
      pip_url: -e tap-gitlab-custom

Let's include the default configuration for a sample tap:

meltano.yml

plugins:
  extractors:
    - capabilities:
      - catalog
      - discover
      - state
      executable: tap-gitlab-custom
      name: tap-gitlab-custom
      namespace: gitlab
      pip_url: -e tap-gitlab-custom
      settings:
        - name: username
        - name: password
          kind: password
        - name: start_date
          value: '2015-09-21T04:00:00Z'

# Plugin Setting

When creating a new plugin, you'll often have to expose some settings to the user so that Meltano can generate the correct configuration to run your plugin.

To expose such a setting, you'll need to define it as such

• name: Identifier of this setting in the configuration.
  The name is the most important field of a setting, as it defines how the value will be passed down to the underlying component.
  Nesting can be represented using the . separator.

  • foo represents the { foo: VALUE } in the output configuration.
  • foo.a represents the { foo: { a: VALUE } } in the output configuration.

• kind: Represent the type of value this should be, (e.g. password or date_iso8601).

• env (optional): Define the environment variable name used to set this value at runtime. Defaults to NAMESPACE_NAME.
• value (optional): Define the default value for this variable. It should also be used as a placeholder for UX purposes.

Once the settings are exposed, you can use any of the following to set the proper values (in order of precedence):

• Environment variables
• config section in the plugin
• Meltano UI
• value of the setting's definition

# Interacting with your new plugin

Now that your plugin is installed and configured, you are ready to interact with it using Meltano.

use meltano invoke to run your plugin in isolation:

meltano invoke tap-gitlab-custom --discover

Use meltano select to parse your catalog:

meltano select --list tap-gitlab-custom '*' '*'

Run an ELT using your new tap:

meltano elt tap-gitlab-custom target-sqlite

# References

• Singer specification
• tap-gitlab
• target-sqlite
• cookiecutter
• singer-tap-template