schema.org_mapping.md

How to map a content type to schema.org

Mapping content types to schema.org properties relies on the custom module mass_schema_metatag. The custom module itself depends on the contrib module schema_metatag as listed under dependencies in mass_schema_metatag.info.yml.

Parent module structure

The custom module contains a .yml file and subfolders:

• mass_schema_metatag.info.yml contains brief module information that we see when we want to enable or disable a module (i.e. /admin/modules). As mentioned above, it has a dependency on schema_metatag contrib module. This latter already exists in the current codebase at the time of writing this guide.
• Each folder sibling to the .yml file, handles a given content type. Example: mass_schema_government_service and mass_schema_apply_action that maps to "Service Page" and "How-To Page" respectively.

│
├── mass_schema_metatag
│   ├── mass_schema_apply_action
│   ├── mass_schema_collection_page
│   ├── mass_schema_government_service
│   ├── mass_schema_metatag.info.yml
│   └── mass_schema_unit_price_specification
│  

Mapping a content type

Mapping a content type starts with documented, discussed and agreed upon field mappings. In fact, the folders mentioned above are modules themselves since they have .yml file, .module file and a src folder. This latter contains the code that handles field mappings with schema.org types and properties. Once a new mapping is in place, make sure that it is enabled here /admin/modules; and that its enabled state is captured in configuration by running drush config-export.

Example: Government Service

In our mass codebase, we map the http://schema.org/GovernmentService to the "Service Page" content type. To view the corresponding schema.org field mappings handled by code in the Tag folder, go to /admin/config/search/metatag and click on "Edit" for the corresponding content type that you are working on. In our example, the relevant path where to view fields and their values is /admin/config/search/metatag/node__service_page. Please note not all fields are mapped due to the way these content types were built; therefore, you may stumble on content types that will not fully map to schema.org.

Government Service folder structure

│
├── mass_schema_government_service
│   ├── mass_schema_government_service.info.yml
│   ├── mass_schema_government_service.module
│   └── src
│       └── Plugin
│           └── metatag
│               ├── Group
│               │   └── SchemaGovernmentService.php
│               └── Tag
│                   ├── SchemaGovernmentServiceAreaServed.php
│                   ├── SchemaGovernmentServiceCategory.php
│                   ├── SchemaGovernmentServiceDescription.php
│                   ├── SchemaGovernmentServiceDisambiguatingDescription.php
│                   ├── SchemaGovernmentServiceId.php
│                   ├── SchemaGovernmentServiceLogo.php
│                   ├── SchemaGovernmentServiceName.php
│                   ├── SchemaGovernmentServicePotentialAction.php
│                   ├── SchemaGovernmentServiceRelatedLink.php
│                   ├── SchemaGovernmentServiceRelatedServices.php
│                   └── SchemaGovernmentServiceType.php
│

Following the directory structure shown above, files live under the folders Group and Tag.

Preprocess functions

It is worth noting here that some values may need pre-processing before they are handed over to the classes in the Tag folder. This is accomplished with the usage of hook_tokens(). For example, if a content type has a field with multiple values e.g. "Related Links", it important to pre-process these and get an array of these links. e.g. "link" and "url". Further validating can include a check whether a links is empty or not …etc. Additional token display can be edited or added by going to /admin/structure/types/manage/<CONTENT_TYPE>/display/ . If you do not see "Token" as an available display, scroll down to the bottom of the page and click "CUSTOM DISPLAY SETTINGS" while you are on the "Default" display mode.

Group folder

Group: Contains SchemaGovernmentService.php file that accomplishes the following:

• Declare a new name space under which the mapping for "GovernmentService" will be contained:

  namespace Drupal\mass_schema_government_service\Plugin\metatag\Group;
  

• Since the work in our custom mass_schema_metatag is an extension of the contrib module schema_metatag, we import the code that helps us with the grouping using:

  use Drupal\schema_metatag\Plugin\metatag\Group\SchemaGroupBase;
  

• Introduce a new class, which is an extension from the contrib module schema_metatag. For now, a placeholder:

  class SchemaGovernmentService extends SchemaGroupBase {
    // Nothing here yet. Just a placeholder class for a plugin.
  }
  

Tag folder

The tag folder contains individual field mappings of the content type in question to schema.org properties.

Example tag: name

In SchemaGovernmentServiceName.php we start with declaring a name space where all these fields/tags will belong to as follow:

namespace Drupal\mass_schema_government_service\Plugin\metatag\Tag;

We also extend the contrib module using by importing some code (i.e. classes and methods)

use Drupal\schema_metatag\Plugin\metatag\Tag\SchemaNameBase;

Now we create the tag name by extending the recently imported SchemaGovernmentServiceName as follow:

class SchemaGovernmentServiceName extends SchemaNameBase {

  /**
   * Generate a form element for this meta tag.
   */
  public function form(array $element = []) {
    $form = parent::form($element);
    $form['#attributes']['placeholder'] = '[node:title]';
    return $form;
  }
}

Note that now the class that handles the schema.org name of this type is called SchemaGovernmentServiceName, for the type you are creating, it may will have a different name e.g. SchemaCoolTypeName. The code snippet above fills out the name with the node title.

Please refer to other files in the tag folder to get more familiar how a field is mapped out.

Notes:

• Some filed are straight forward to map out e.g. node title.
• Entity reference fields need further code crafting.
• Fields with multiple values entity reference or not may need graceful loop iteration over the multiple values.