Addons: Single vs List Return Types

In Xano, add-ons are a powerful tool that allow you to enhance your API responses with related data from other tables. One common question that arises is when to use a list return type or a single return type when creating add-ons. In this guide, we'll walk through some examples to help you understand the difference and make the right choice based on the relationships between your data models.

Understanding the Relationship: One-to-One vs. One-to-Many

The decision to use a list or single return type depends on the relationship between the tables you're working with. Let's explore two common scenarios:

One-to-One Relationship

In a one-to-one relationship, each record in one table can only be associated with a single record in another table. For example, consider a `users` table and a `locations` table, where each user can only belong to one location.

To retrieve user data along with their location information, you would use a single return type for the add-on. Here's how you can set it up:

1. Go to your `users` endpoint and navigate to the "Query All Records" section.
2. Click on the "Add-on" button and select "Create New Add-on."
3. Choose the `locations` table.
4. Select "Single Item" as the return type.
5. Map the `location_id` field from the `users` table to the `id` field of the `locations` table.
6. Save and run the endpoint.

Your response will include user records with a nested `location` object containing the corresponding location details.

One-to-Many Relationship

In a one-to-many relationship, each record in one table can be associated with multiple records in another table. For instance, consider a `projects` table and a `users` table, where each project can have multiple users assigned to it.

To retrieve project data along with the list of users working on each project, you would use a list return type for the add-on. Follow these steps:

1. Go to your `projects` endpoint and navigate to the "Query All Records" section.
2. Click on the "Add-on" button and select "Create New Add-on."
3. Choose the `users` table.
4. Select "List of Items" as the return type.
5. Map the `user_id` field from the `projects` table to the `id` field of the `users` table.
6. Save and run the endpoint.

Your response will include project records with a nested array of `user` objects representing the team members assigned to each project.

Handling Many-to-Many Relationships

In some cases, you may encounter a many-to-many relationship, where records in one table can be associated with multiple records in another table, and vice versa. For example, a `users` table and a `projects` table, where users can work on multiple projects, and projects can have multiple users assigned to them.

To handle this scenario, you'll need to create a custom add-on using the Xano library. Here's how you can do it:

1. Go to the "Add-ons" page in the Xano library.
2. Click on "Create New Add-on."
3. Select the `projects` table.
4. Choose "List of Items" as the return type.
5. Instead of mapping a field, click on "Add Custom Query."
6. In the custom query editor, use the `in` operator to check if a `user_id` from the `users` table is present in the `user_ids` array of the `projects` table.
7. Save the add-on and map it to your `users` endpoint.

By using a custom query with the `in` operator, you can retrieve a list of projects for each user, even in a many-to-many relationship.

Customizing Add-ons

Xano provides the flexibility to customize add-ons even after they're created. If you realize you've chosen the wrong return type or need to modify the mapping, you can simply go to the "Add-ons" page in the library, select the add-on you want to edit, and make the necessary changes.

Conclusion

Choosing between a list or single return type when creating add-ons in Xano depends on the relationships between your data models. By understanding one-to-one, one-to-many, and many-to-many relationships, you can ensure that your API responses include the related data in the desired format. Additionally, Xano's custom add-on feature allows you to handle complex scenarios and tailor the responses to your specific needs.

Remember, the key is to analyze the relationships between your tables and select the appropriate return type accordingly. With Xano's visual interface and powerful add-on capabilities, building and deploying backend services for your web and mobile applications has never been easier, regardless of your technical background.