This page refers to the extends parameter that is part of a view.

extends can also be used as part of an Explore, described on the extends (for Explores) parameter documentation page.

extends can also be used as part of a LookML dashboard, described on the Dashboard parameters documentation page.

Usage

Definition

The extends parameter lets you build upon the content and settings from another view file, using the other view file as a starting point. If there are any conflicts, the extending view will use its own settings, overriding the settings of the view being extended. See Reusing code with extends for the details of how Looker does this.

Check out LookML refinements.
Extending a view or an Explore is ideal for scenarios where you want to have multiple versions of the view or Explore. But if your goal is simply to modify a view or an Explore without editing the LookML file that contains it, you may want to use a refinement instead. You can also use an extends parameter inside a refinement. See the LookML refinements documentation page for more information and use cases.

When extending a view, it’s important to use the sql_table_name parameter on the view that is going to be extended, if it’s not already there. The sql_table_name parameter defines the table in your database that will be queried by a view. For any view the default value is the name of the view. So, if you aren’t already using sql_table_name, simply give it the same value as your view name.

It’s also important that in our new view file we use the include parameter to point to the filename of the view we want to extend.

Avoid extending views that are based on persistent derived tables (PDTs). Each extension of a PDT will create a new copy of the table in your database. In this case, you may want to use LookML refinements instead. See the LookML refinements documentation page for more information and use cases.

Example

Here’s an example view file that we can extend. The view is named looker_events and the view’s filename is events.view.

File: events.view

Now we’ll create a new view file and define a view that extends the looker_events view. In our new file, we must use the include parameter to point to the file name of the view we want to extend:

File: new_events.view

And then we’ve added a new measure that will show in our new view in addition to all the dimensions and measures that are defined in the looker_events view that we extended.

Using metadata to see extensions for an object

If your Looker admin has enabled the IDE Metadata Sidebar Labs feature, you can click on an explore or a view parameter in the Looker IDE and use the metadata panel to see any extensions on the object, or to see what object it extends. See the Metadata for LookML objects documentation page for information.

Things to consider

Some parameters are additive

In many cases, if the extending object contains the same parameter as the object that is being extended, the extending object’s values will override the parameter values of the extended object.

But extensions can be additive for some parameters, meaning that the values from the extending object are used in conjunction with the values from the extended object.

The following parameters are additive:

• For dimensions and measures:

  • action
  • filters
  • link

• For views:

  • extends (you can chain together multiple extends)

In the following example, the carriers view has a name dimension with a link parameter:

And here is the carriers_extended view, which extends the carriers view. The carriers_extended view also has a name dimension with different settings in the link parameter:

In the carriers_extended view, the two link parameters are additive, so the name dimension will have both links. The dimension looks like this in an Explore:

Projects with localization

When extending an object, be aware that localization rules apply to your extensions as well. If you are extending an object and then defining new labels or descriptions, you should provide localization definitions in your project’s locale strings files. See the Localizing your LookML model documentation page for more information.