YAML Selectors

▶Changelog

Write resource selectors in YAML, save them with a human-friendly name, and reference them using the --selector flag. By recording selectors in a top-level selectors.yml file:

• Legibility: complex selection criteria are composed of dictionaries and arrays
• Version control: selector definitions are stored in the same git repository as the dbt project
• Reusability: selectors can be referenced in multiple job definitions, and their definitions are extensible (via YAML anchors)

Selectors live in a top-level file named selectors.yml. Each must have a name and a definition, and can optionally define a description and default flag.

selectors.yml

selectors:
  - name: nodes_to_joy
    definition: ...
  - name: nodes_to_a_grecian_urn
    description: Attic shape with a fair attitude
    default: true
    definition: ...

Definitions

Each definition is comprised of one or more arguments, which can be one of the following:

• CLI-style: strings, representing CLI-style) arguments
• Key-value: pairs in the form method: value
• Full YAML: fully specified dictionaries with items for method, value, operator-equivalent keywords, and support for exclude

Use union and intersection to organize multiple arguments.

CLI-style

definition:
  'tag:nightly'

This simple syntax supports use of the +, @, and * operators. It does not support exclude.

Key-value

definition:
  tag: nightly

This simple syntax does not support any operators or exclude.

Full YAML

This is the most thorough syntax, which can include graph and set operators.

definition:
  method: tag
  value: nightly

  # Optional keywords map to the `+` and `@` operators:

  children: true | false
  parents: true | false

  children_depth: 1    # if children: true, degrees to include
  parents_depth: 1     # if parents: true, degrees to include

  childrens_parents: true | false     # @ operator
  
  greedy: true | false  # include all tests selected indirectly? false by default

The * operator to select all nodes can be written as:

definition:
  method: fqn
  value: "*"

Exclude

The exclude keyword is only supported by fully-qualified dictionaries. It may be passed as an argument to each dictionary, or as an item in a union. The following are equivalent:

- method: tag
  value: nightly
  exclude:
    - "@tag:daily"

- union:
    - method: tag
      value: nightly
    - exclude:
       - method: tag
         value: daily

Note: The exclude argument in YAML selectors is subtly different from the --exclude CLI argument. Here, exclude always returns a set difference, and it is always applied last within its scope.

This gets us more intricate subset definitions than what's available on the CLI, where we can only pass one "yeslist" (--select) and one "nolist" (--exclude).

Greedy

As a general rule, dbt will indirectly select tests if they touch resources that you're selecting directly, but not tests that also touch unselected resources (e.g. a relationships test, with one parent selected and one parent not selected). Starting in v0.21, you can optionally turn this on by setting greedy: true for a specific criterion:

- union:
    - method: fqn
      value: model_a
      greedy: true  # will include all tests that touch model_a
    - method: fqn
      value: model_b
      greedy: false  # default: will not include tests touching model_b
                     # if they have other unselected parents

In CLI-based selection, dbt will warn you about tests that aren't greedily included. Here, you're in "full control" mode—dbt will not warn you about which tests your yaml selector definition does or does not include. Remember that you can always use list to check.

See test selection examples for more details about greediness and indirect selection.

Example

Here are two ways to represent:

$ dbt run --select @source:snowplow,tag:nightly models/export --exclude package:snowplow,config.materialized:incremental export_performance_timing

• CLI-style
• Full YML

selectors.yml

selectors:
  - name: nightly_diet_snowplow
    description: "Non-incremental Snowplow models that power nightly exports"
    definition:
      union:
        - intersection:
            - '@source:snowplow'
            - 'tag:nightly'
        - 'models/export'
        - exclude:
            - intersection:
                - 'package:snowplow'
                - 'config.materialized:incremental'
            - export_performance_timing

Then in our job definition:

$ dbt run --selector nightly_diet_snowplow

Default

Starting in v0.21, selectors may define a boolean default property. If a selector has default: true, dbt will use this selector's criteria when tasks do not define their own selection criteria.

Let's say we define a default selector that only selects resources defined in our root project:

selectors:
  - name: root_project_only
    description: >
        Only resources from the root project.
        Excludes resources defined in installed packages.
    default: true
    definition:
      method: project
      value: <my_root_project_name>

If I run an "unqualified" command, dbt will use the selection criteria defined in root_project_only—that is, dbt will only build / freshness check / generate compiled SQL for resources defined in my root project.

$ dbt build
$ dbt source freshness
$ dbt docs generate

If I run a command that defines its own selection criteria (via --select, --exclude, or --selector), dbt will ignore the default selector and use the flag criteria instead. It will not try to combine the two.

$ dbt run --select  model_a
$ dbt run --exclude model_a

Only one selector may set default: true for a given invocation; otherwise, dbt will return an error. You may use a Jinja expression to adjust the value of default depending on the environment, however:

selectors:
  - name: default_for_dev
    default: "{{ target.name == 'dev' | as_bool }}"
    definition: ...
  - name: default_for_prod
    default: "{{ target.name == 'prod' | as_bool }}"
    definition: ...