Developer Instructions for 8.1 Branch

Extending an existing schema

Schema.org Metatag module contains an example module, schema_article_example, that shows how the Article schema can be extended without altering the schema_article module itself. Using this as a template basically only entails file name changes, and naming edits in the code. This is a great option if the extension is for an arcane property, or proprietary to you.  It is also useful since future module updates won't overwrite your code.

Alternatively, you can extend one of the existing submodules. We recommend you check out the current development branch via git for this. Then post your patch to the issue queue for inclusion into the module. This is your best option if the extension is of broad value to most folks, such as adding a property required or recommended by search engines.

Adding support for a new schema

For a completely new schema, let's use the Service schema as an example. A review of schema.org/Service shows that Service has many of the same properties as Product. So as a decent first cut we will clone the schema_product module. Use an analogous approach for any other schemas.

1. Copy the schema_product directory and name it schema_service. Rename each file in schema_service to contain service in its name instead of product.
2. Go through all code files and change product to service. You will find lowercase and uppercase instances, change them all and retain case.
3. You may want to edit description text for certain types. Generally these should match what you find at schema.org, but you can often do better by being more precise.
4. Clear Drupal cache, and enable your new module. If none is found you haven't completed your renaming.
5. Go to /admin/config/metatag and check whether your new schema shows up, and then check whether all fields show up correctly and are free of typos.
6. The only tricky part of this process is finding the right base class to use for each property. A simple text or numeric value would use the default class, SchemaNameBase. More complicated properties will extend other classes. A partial list is below.
7. Test your submodule on a node or sitewide by filling in values or tokens, and check the output on a relevant node.
8. Run the JSON-LD code through Google's validator at https://search.google.com/test/rich-results.
9. Create a patch from your code and post it into a new issue in Schema.org Metatag's issue queue.

Available base classes

The list of available base classes changes frequently, but a partial list is below. Look in the "/src/Plugin/metatag/Tag" directory of your repository to see the complete list. For example, on http://schema.org/Article there is an 'author' property that should be either a http://schema.org/Person object or a http://schema.org/Organization object. You would set up the 'author' tag to extend the 'SchemaPersonOrg' class.

Default objects

• SchemaNameBase - the default class, suitable for simple text or numeric values.
• SchemaTypeBase - for the '@type' property used on all objects.

Thing objects

• SchemaPersonOrgBase - for a property that is either a Person or Organization.
• SchemaEventBase - for a property that is an Event.
• SchemaImageBase - for a property that is an Image.
• SchemaCreativeWorkBase - for a property that is any type of CreativeWork.
• SchemaThingBase - for a property that is any type of Thing.

Location objects

• SchemaAddressBase - for a property that is an Address object.
• SchemaGeoBase - for a property that is geographic coordinates.
• SchemaPlaceBase - a Place object, a complex object that includes the name of a place along with an embedded Address object and A Geo object.
• SchemaCountryBase - a property that is a Country object.

Miscellaneous objects

• SchemaActionBase - for a property that is an Action object.
• SchemaDateBase - for a property that is a Date or Datetime object.
• SchemaDurationBase - for a property that is a Duration object.
• SchemaOfferBase - for a property that is an Offer object.
• SchemaProgramMembershipBase - for a property that is a ProgramMembership object.