Usage

Definition

The constant parameter defines a LookML constant, allowing you to specify a value that can be reused throughout a project. Constants can be referenced anywhere in the model where strings are accepted and with the model and explore parameters of a LookML dashboard element, thus helping reduce repetition in your LookML code.

Constants must be defined in the project manifest file. Constants may then be used throughout a project using @{constant_name} syntax.

You can use the export subparameter of constant to specify whether developers should override the value of a constant when files that reference it are imported into another project.

export

You can use the export subparameter of constant to determine how a constant can be used when files that reference that constant are imported into other projects.

By default, imported files that reference a constant use the value specified in the imported project’s manifest file in the importing project. The export parameter specifies whether developers should override a constant’s value by providing a new value for that constant to use in importing projects. The export parameter has the following possible values:

• none: The default value for export. The constant’s value cannot be overridden in the importing project. The importing project uses the constant value specified in the imported project’s manifest file.
• override_optional: The constant’s value can optionally be overridden in your importing project. If a value is not provided in the importing project’s manifest file, the original value from the imported project is used.
• override_required: The importing project must override the constant value originally specified in the imported project’s manifest file. If a new constant value is not provided in the importing project, Looker will display an error.

Constants are available only to files from the project in which they are originally defined. Therefore, constants that are defined in a project whose files you have imported can be used only by the imported files, and not by files defined in the importing project.

If you want to use a constant in the importing project’s files, you should define a new constant in the importing project’s manifest file. A constant defined in this way will be available only to the files defined in the importing project.

When you import files that reference a constant into another project, you can use the override_constant subparameter of local_dependency or remote_dependency in the importing project’s manifest file to provide a new value for a constant that has export set to override_optional or override_required.

See the Importing files from other projects documentation page for more information and an example of overriding constants in importing projects.

Examples

Here are some examples of how you can use the constant parameter to define values that can be used throughout a project.

Labeling Explores with the constant parameter

Suppose you want to create two Explores, labeled San Francisco Users and San Francisco Orders in the UI. To do this, you can define a constant city with the value "San Francisco" in the manifest.lkml file for your project:

This constant can then be referenced in any part of your project where a string is accepted, using the syntax @{city}. In this example, you can define the users and orders Explores, specifying "@{city} Users" and "@{city} Orders" as values for the label parameter, as in the following example:

In this example, Looker displays San Francisco Users and San Francisco Orders in the Explore menu and in the titles of the Explores, rather than the default Users and Orders labels:

Using the sql_table_name parameter with constants

Let’s suppose you want to create several views based on tables in the schema 02349_sfo. To avoid having to specify the value 02349_sfo multiple times, you create a constant named schema in the manifest.lkml file for your project, as follows:

You can then create views based on the 02349_sfo schema by specifying @{schema}.view_name as the value for the sql_table_name parameter:

This creates a view called Users that is based on the users table from the schema 02349_sfo.

Using Liquid variables and HTML with constants

Imagine that you want negative data values to be displayed within parentheses and in a red font. By setting this formatting as the value for a LookML constant, you can specify the formatting just once using Liquid variables and HTML. Then, you can reference the constant whenever you want to apply that formatting to a field.

For example, you can create a constant negative_format with which to apply this formatting to a field:

This creates a constant negative_format that specifies that negative data values should have a red font and be surrounded by parentheses. You can then apply this formatting to dimensions and measures in your dataset using the html parameter.

For example, you can create Total Amount measure of type: sum and specify @{negative_format} as the value for the html parameter:

In your table, negative values for the Total Amount measure will be formatted as specified in the negative_format constant definition, with a red font and surrounded by parentheses:

Using constants in LookML dashboards

When you define a dashboard element for a LookML dashboard, you can use LookML constants to define the model and Explore that an element is based on.

As an example, suppose you have defined the constants model_name and explore_name in the manifest.lkml file for your project:

In your dashboard file, you can set the value of model to "@{model_name}" and set the value of explore to "@{explore_name}" for any dashboard elements that you want to be based on the model thelook and the Explore orders.

For example, suppose you’re editing the LookML for a column chart element. In the dashboard file, you can specify the values for the model and explore parameters as follows:

Things to know

Referring to constants within a constant definition

When defining a constant, you can reference other constants defined within the manifest file for your project. Suppose you have already declared a constant city:

You may then declare a constant state that references the city constant in the example above:

The constant state declared above will resolve to the string “San Francisco, California”.

Escaping constant syntax

When you want to write a string that resembles constant syntax, but you don’t want that string to be evaluated as a constant, you can escape the constant syntax using the backslash escape character \ after the @ character. For example:

In the above example, the label parameter displays the string @{id} as the label for the id dimension, rather than evaluating the id constant and outputting its value.

Constant references will not be evaluated if the brackets are not closed, in which case it is not necessary to escape constant syntax. Thus, @{id in the example below would not be evaluated as a constant.