Using virtual foreign keys

Tutorial

"Virtual foreign keys" are a powerful feature that allow you to impose virtual foreign key relationships between data in unrelated tables. Tables can be either in the same database or in different databases, and you don't need to alter the database schema. Virtual foreign keys are a convenient way to orchestrate complex queries on disparate data without having to hand-code server-side logic.

Once you've set up a virtual foreign key relationship, it's easy to perform CRUD operations that read, write, update, and delete records on the "virtually" related data, all with a single API call that passes the virtual foreign key as an API parameter. Try these examples in the 'API Docs' tab of the DreamFactory Admin Console or from the command line with cURL.

API Endpoint

GET https://{url}/api/v2/{api_name}/_table/{table_name}?related={virtual_foreign_key_field}

API Docs Screenshot

Example - Fetch contact and related customer records in the same database with username as a virtual foreign key.

Say we have two tables in the same database that we need to connect: a 'contact' table with basic contact information and a 'customer' table that lists transactions of items we've sold to customers. These tables don't have a foreign key relationship in our database schema, but the contact table has a field called 'email' and the customer table has a field called 'username', which is an email address.

We can use the customer table's 'username' field as a virtual foreign key to the contact table's 'email' field, allowing us to make a single API call to GET a set of contact records and related records in the customer table where the customer 'username' matches contact 'email'.

To set up the virtual foreign key, navigate to the Schema tab and select the field you want to be a virtual foreign key. In this example, we select the 'username' field on the 'contact' table. Then in the 'username' field definition form, check 'Foreign Key', 'Virtual Foreign Key', 'contact' for Reference Table, and 'email' for 'Reference' field.

To see the virtual foreign key relationship from the 'contact' table, go to Schema and select the 'contact' table. Under Relationships, you'll see that 'contact' now has a 'has_many' relationship to the customer table.

Now we can make API calls to the 'contact' table and GET both contacts and related customer records in a single API call.

• Table name: contact
• Related parameter in API call:

  customer_by_username

• Request URL:

  https://foo.com/api/v2/mysql/_table/contact?related=customer_by_username

Example - Fetch contact and related customer records in a different database with username as a virtual foreign key.

This example is similar to the previous example, except that the tables reside in two completely different databases (for example, two different MySQL databases or one SQL Server database and an Oracle database). Say that we need to connect a 'contact' table in database one with a 'customer' table in database two. These tables obviously can't have a foreign key relationship in our database schema, but the contact table has a field called 'email' and the customer table has a field called 'username', which is an email address.

Even though the tables reside in two isolated databases, we can still use the customer table's 'username' field as a virtual foreign key to the contact table's 'email' field, allowing us to make a single API call to GET a set of contact records and related records in the customer table where the customer 'username' matches contact 'email'.

To set up the virtual foreign key, navigate to the Schema tab and select the field you want to be a virtual foreign key. In this example, we select the 'username' field on the 'contact' table. Then in the 'username' field definition form, check 'Foreign Key', 'Virtual Foreign Key', 'Foreign Reference Service', the name of the database where the 'contact' table resides, 'contact' for Reference Table, and 'email' for 'Reference' field.

To see the virtual foreign key relationship from the 'contact' table, go to Schema and select the 'contact' table. Under Relationships, you'll see that 'contact' now has a 'has_many' relationship to the customer table that's in a completely different database.

Now we can make API calls to the 'contact' table and GET both contacts and related customer records in a single API call. The API call is the same as the previous example, except that the related field name (our virtual foreign key) is prefixed by the database service (API name) where it resides. In this example, the 'customer' table is in a database service called 'db' while the 'contact' table is in a different database service called 'mysql'.

• Table name: contact
• Related parameter in API call:

  db.customer_by_username

• Request URL:

  https://foo.com/api/v2/mysql/_table/contact?related=db.customer_by_username