An API "get" action will typically return only the values of the entity requested. However, there are times when it is advantageous to returned data from a related entity. For instance, when querying the API for email addresses, you may want to return the name of the associated contact from the Contact entity.
The CiviCRM API supports two methods of returning data from associated entities; API Joins and APIv3 Chaining. API joins provide higher performance by making a single SQL query with a SQL join, and are generally preferable to API chaining where available.
Using an API Join¶
To use a join in an API call, specify the name of the field on which the join happens, a period, and the name of the field to reference.
For instance, to search for all primary emails, returning the email and joining to also return the contact's display name:
$result = civicrm_api3('Email', 'get', array( 'return' => array("email", "contact_id.display_name"), 'is_primary' => 1, ));
Alternatively, to return email addresses of everyone whose last name is Smith by joining to the Contact entity:
$result = civicrm_api3('Email', 'get', array( 'contact_id.last_name' => "Smith", ));
Identifying fields eligible for a join¶
Not supported for every entity
For historical reasons, some entities have a non-standard API in APIv3 in order to handle more complicated operations. Those entities - 'Contact', 'Contribution', 'Pledge', and 'Participant' - can be joined to from another table, but you can not join to other tables from them. APIv4 does not have this limitation.