Using variables

dbt provides a mechanism, variables, to provide data to models for compilation. Variables can be used to configure timezones, avoid hardcoding table names or otherwise provide data to models to configure how they are compiled.

To use a variable in a model, hook, or macro, use the {{ var('...') }} function. More information on the var function can be found here.

Variables can defined in two ways:

  1. In the dbt_project.yml file
  2. On the command line

Defining variables in dbt_project.yml

To supply a variable to a given model, add a vars dictionary to the models: config in your dbt_project.yml file. These vars are in-scope for all models at or below where they are defined, so place them where they make the most sense.

materialized: view
# Configure a start date for the models in the events/ directory.
# This will avoid the need to hardcode '2016-06-01' in all of your models!
start_date: '2016-06-01'

Defining variables on the command line

The dbt_project.yml file is a great place to define variables that rarely change. Other types of variables, like date ranges, will change frequently. To define (or override) variables for a run of dbt, use the --vars command line option. In practice, this looks like:

$ dbt run --vars '{"key": "value"}'

The --vars argument accepts a YAML dictionary as a string on the command line. YAML is convenient because it does not require strict quoting as with JSON.

Both of the following are valid and equivalent:

$ dbt run --vars '{"key": "value", "date": 20180101}'
$ dbt run --vars '{key: value, date: 20180101}'

If only one variable is being set, the brackets are optional, eg:

$ dbt run --vars 'key: value'

You can find more information on defining dictionaries with YAML here.

Variable precedence

Variables defined with the --vars command line argument are applied at the "root" level, as though they were defined directly under models: in the dbt_project.yml file. Variables defined on the command line will take precedence over all variable declarations defined anywhere else in your project or its dependencies.

The order of precedence for variable declaration is as follows (highest priority first):

  1. The variables defined on the command line with --vars.
  2. The most specific variable definition in the root dbt_project.yml file.
  3. The most specific variable definition in the model's own dbt_project.yml file (if this model or macro is in a package).
  4. The variable's default argument (if one is provided).

If dbt is unable to find a definition for a variable after checking these four places, then a compilation error will be raised.