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Contributing to dbt

  1. About this document
  2. Proposing a change
  3. Getting the code
  4. Setting up an environment
  5. Running dbt in development
  6. Testing
  7. Submitting a Pull Request

About this document

This document is a guide intended for folks interested in contributing to dbt. Below, we document the process by which members of the community should create issues and submit pull requests (PRs) in this repository. It is not intended as a guide for using dbt, and it assumes a certain level of familiarity with Python concepts such as virtualenvs, pip, python modules, filesystems, and so on. This guide assumes you are using macOS or Linux and are comfortable with the command line.

If you're new to python development or contributing to open-source software, we encourage you to read this document from start to finish. If you get stuck, drop us a line in the #dbt-core-development channel on slack.

Signing the CLA

Please note that all contributors to dbt must sign the Contributor License Agreement to have their Pull Request merged into the dbt codebase. If you are unable to sign the CLA, then the dbt maintainers will unfortunately be unable to merge your Pull Request. You are, however, welcome to open issues and comment on existing ones.

Proposing a change

dbt is Apache 2.0-licensed open source software. dbt is what it is today because community members like you have opened issues, provided feedback, and contributed to the knowledge loop for the entire communtiy. Whether you are a seasoned open source contributor or a first-time committer, we welcome and encourage you to contribute code, documentation, ideas, or problem statements to this project.

Defining the problem

If you have an idea for a new feature or if you've discovered a bug in dbt, the first step is to open an issue. Please check the list of open issues before creating a new one. If you find a relevant issue, please add a comment to the open issue instead of creating a new one. There are hundreds of open issues in this repository and it can be hard to know where to look for a relevant open issue. The dbt maintainers are always happy to point contributors in the right direction, so please err on the side of documenting your idea in a new issue if you are unsure where a problem statement belongs.

Note: All community-contributed Pull Requests must be associated with an open issue. If you submit a Pull Request that does not pertain to an open issue, you will be asked to create an issue describing the problem before the Pull Request can be reviewed.

Discussing the idea

After you open an issue, a dbt maintainer will follow up by commenting on your issue (usually within 1-3 days) to explore your idea further and advise on how to implement the suggested changes. In many cases, community members will chime in with their own thoughts on the problem statement. If you as the issue creator are interested in submitting a Pull Request to address the issue, you should indicate this in the body of the issue. The dbt maintainers are always happy to help contributors with the implementation of fixes and features, so please also indicate if there's anything you're unsure about or could use guidance around in the issue.

Submitting a change

If an issue is appropriately well scoped and describes a beneficial change to the dbt codebase, then anyone may submit a Pull Request to implement the functionality described in the issue. See the sections below on how to do this.

The dbt maintainers will add a good first issue label if an issue is suitable for a first-time contributor. This label often means that the required code change is small, limited to one database adapter, or a net-new addition that does not impact existing functionality. You can see the list of currently open issues on the Contribute page.

Here's a good workflow:

  • Comment on the open issue, expressing your interest in contributing the required code change
  • Outline your planned implementation. If you want help getting started, ask!
  • Follow the steps outlined below to develop locally. Once you have opened a PR, one of the dbt maintainers will work with you to review your code.
  • Add a test! Tests are crucial for both fixes and new features alike. We want to make sure that code works as intended, and that it avoids any bugs previously encountered. Currently, the best resource for understanding dbt's unit and integration tests is the tests themselves. One of the maintainers can help by pointing out relevant examples.

In some cases, the right resolution to an open issue might be tangential to the dbt codebase. The right path forward might be a documentation update or a change that can be made in user-space. In other cases, the issue might describe functionality that the dbt maintainers are unwilling or unable to incorporate into the dbt codebase. When it is determined that an open issue describes functionality that will not translate to a code change in the dbt repository, the issue will be tagged with the wontfix label (see below) and closed.

Using issue labels

The dbt maintainers use labels to categorize open issues. Some labels indicate the databases impacted by the issue, while others describe the domain in the dbt codebase germane to the discussion. While most of these labels are self-explanatory (eg. snowflake or bigquery), there are others that are worth describing.

tag description
triage This is a new issue which has not yet been reviewed by a dbt maintainer. This label is removed when a maintainer reviews and responds to the issue.
bug This issue represents a defect or regression in dbt
enhancement This issue represents net-new functionality in dbt
good first issue This issue does not require deep knowledge of the dbt codebase to implement. This issue is appropriate for a first-time contributor.
help wanted / discussion Conversation around this issue in ongoing, and there isn't yet a clear path forward. Input from community members is most welcome.
duplicate This issue is functionally identical to another open issue. The dbt maintainers will close this issue and encourage community members to focus conversation on the other one.
snoozed This issue describes a good idea, but one which will probably not be addressed in a six-month time horizon. The dbt maintainers will revist these issues periodically and re-prioritize them accordingly.
stale This is an old issue which has not recently been updated. Stale issues will periodically be closed by dbt maintainers, but they can be re-opened if the discussion is restarted.
wontfix This issue does not require a code change in the dbt repository, or the maintainers are unwilling/unable to merge a Pull Request which implements the behavior described in the issue.

Branching Strategy

dbt has three types of branches:

  • Trunks are where active development of the next release takes place. There is one trunk named develop at the time of writing this, and will be the default branch of the repository.
  • Release Branches track a specific, not yet complete release of dbt. Each minor version release has a corresponding release branch. For example, the 0.11.x series of releases has a branch called 0.11.latest. This allows us to release new patch versions under 0.11 without necessarily needing to pull them into the latest version of dbt.
  • Feature Branches track individual features and fixes. On completion they should be merged into the trunk brnach or a specific release branch.

Getting the code

Installing git

You will need git in order to download and modify the dbt source code. On macOS, the best way to download git is to just install Xcode.

External contributors

If you are not a member of the fishtown-analytics GitHub organization, you can contribute to dbt by forking the dbt repository. For a detailed overview on forking, check out the GitHub docs on forking. In short, you will need to:

  1. fork the dbt repository
  2. clone your fork locally
  3. check out a new branch for your proposed changes
  4. push changes to your fork
  5. open a pull request against fishtown-analytics/dbt from your forked repository

Core contributors

If you are a member of the fishtown-analytics GitHub organization, you will have push access to the dbt repo. Rather than forking dbt to make your changes, just clone the repository, check out a new branch, and push directly to that branch.

Setting up an environment

There are some tools that will be helpful to you in developing locally. While this is the list relevant for dbt development, many of these tools are used commonly across open-source python projects.

Tools

A short list of tools used in dbt testing that will be helpful to your understanding:

  • tox to manage virtualenvs across python versions. We currently target the latest patch releases for Python 3.6, Python 3.7, Python 3.8, and Python 3.9
  • pytest to discover/run tests
  • make - but don't worry too much, nobody really understands how make works and our Makefile is super simple
  • flake8 for code linting
  • mypy for static type checking
  • CircleCI and Azure Pipelines

A deep understanding of these tools in not required to effectively contribute to dbt, but we recommend checking out the attached documentation if you're interested in learning more about them.

virtual environments

We strongly recommend using virtual environments when developing code in dbt. We recommend creating this virtualenv in the root of the dbt repository. To create a new virtualenv, run:

python3 -m venv env
source env/bin/activate

This will create and activate a new Python virtual environment.

docker and docker-compose

Docker and docker-compose are both used in testing. Specific instructions for you OS can be found here.

postgres (optional)

For testing, and later in the examples in this document, you may want to have psql available so you can poke around in the database and see what happened. We recommend that you use homebrew for that on macOS, and your package manager on Linux. You can install any version of the postgres client that you'd like. On macOS, with homebrew setup, you can run:

brew install postgresql

Running dbt in development

Installation

First make sure that you set up your virtualenv as described in Setting up an environment. Next, install dbt (and its dependencies) with:

make dev
# or
pip install -r dev-requirements.txt -r editable-requirements.txt

When dbt is installed this way, any changes you make to the dbt source code will be reflected immediately in your next dbt run.

Running dbt

With your virtualenv activated, the dbt script should point back to the source code you've cloned on your machine. You can verify this by running which dbt. This command should show you a path to an executable in your virtualenv.

Configure your profile as necessary to connect to your target databases. It may be a good idea to add a new profile pointing to a local postgres instance, or a specific test sandbox within your data warehouse if appropriate.

Testing

Getting the dbt integration tests set up in your local environment will be very helpful as you start to make changes to your local version of dbt. The section that follows outlines some helpful tips for setting up the test environment.

Since dbt works with a number of different databases, you will need to supply credentials for one or more of these databases in your test environment. Most organizations don't have access to each of a BigQuery, Redshift, Snowflake, and Postgres database, so it's likely that you will be unable to run every integration test locally. Fortunately, Fishtown Analytics provides a CI environment with access to sandboxed Redshift, Snowflake, BigQuery, and Postgres databases. See the section on Submitting a Pull Request below for more information on this CI setup.

Initial setup

We recommend starting with dbt's Postgres tests. These tests cover most of the functionality in dbt, are the fastest to run, and are the easiest to set up. To run the Postgres integration tests, you'll have to do one extra step of setting up the test database:

make setup-db

or, alternatively:

docker-compose up -d database
PGHOST=localhost PGUSER=root PGPASSWORD=password PGDATABASE=postgres bash test/setup_db.sh

dbt uses test credentials specified in a test.env file in the root of the repository for non-Postgres databases. This test.env file is git-ignored, but please be extra careful to never check in credentials or other sensitive information when developing against dbt. To create your test.env file, copy the provided sample file, then supply your relevant credentials. This step is only required to use non-Postgres databases.

cp test.env.sample test.env
$EDITOR test.env

In general, it's most important to have successful unit and Postgres tests. Once you open a PR, dbt will automatically run integration tests for the other three core database adapters. Of course, if you are a BigQuery user, contributing a BigQuery-only feature, it's important to run BigQuery tests as well.

Test commands

There are a few methods for running tests locally.

Makefile

There are multiple targets in the Makefile to run common test suites and code checks, most notably:

# Runs unit tests with py38 and code checks in parallel.
make test
# Runs postgres integration tests with py38 in "fail fast" mode.
make integration

These make targets assume you have a recent version of tox installed locally, unless you use choose a Docker container to run tests. Run make help for more info.

Check out the other targets in the Makefile to see other commonly used test suites.

tox

tox takes care of managing virtualenvs and install dependencies in order to run tests. You can also run tests in parallel, for example, you can run unit tests for Python 3.6, Python 3.7, Python 3.8, flake8 checks, and mypy checks in parallel with tox -p. Also, you can run unit tests for specific python versions with tox -e py36. The configuration for these tests in located in tox.ini.

pytest

Finally, you can also run a specific test or group of tests using pytest directly. With a virtualenv active and dev dependencies installed you can do things like:

# run specific postgres integration tests
python -m pytest -m profile_postgres test/integration/001_simple_copy_test
# run all unit tests in a file
python -m pytest test/unit/test_graph.py
# run a specific unit test
python -m pytest test/unit/test_graph.py::GraphTest::test__dependency_list

Here is a list of useful command-line options for pytest to use while developing.

Submitting a Pull Request

Fishtown Analytics provides a sandboxed Redshift, Snowflake, and BigQuery database for use in a CI environment. When pull requests are submitted to the fishtown-analytics/dbt repo, GitHub will trigger automated tests in CircleCI and Azure Pipelines.

A dbt maintainer will review your PR. They may suggest code revision for style or clarity, or request that you add unit or integration test(s). These are good things! We believe that, with a little bit of help, anyone can contribute high-quality code.

Once all tests are passing and your PR has been approved, a dbt maintainer will merge your changes into the active development branch. And that's it! Happy developing 🎉