How to Properly Type Supabase Responses When Using JOIN Operations in TypeScript?

Supabase is a powerful open-source alternative to Firebase that provides a real-time database and authentication system. When working with Supabase and TypeScript, you may come across a situation where you need to perform JOIN operations on your database tables. In this blog post, we will explore how to properly type Supabase responses when using JOIN operations in TypeScript.

Understanding JOIN Operations in Supabase

JOIN operations in Supabase allow you to combine rows from two or more tables based on a related column between them. This is useful when you need to fetch data from multiple tables and join them together to get a comprehensive result.

Let’s say we have two tables in our Supabase database: users and orders. The users table contains information about the users, and the orders table contains information about the orders made by the users. We want to fetch all the orders along with the corresponding user information.

Solution 1: Using Interfaces

One way to properly type Supabase responses when using JOIN operations is by using interfaces. Interfaces allow you to define the structure of an object, which can be used to type the response data.

First, let’s define the interfaces for our users and orders tables:


interface User {
  id: number;
  name: string;
  email: string;
}

interface Order {
  id: number;
  userId: number;
  amount: number;
}

Next, we can define a new interface that combines the User and Order interfaces to represent the joined response:


interface UserOrder {
  user: User;
  order: Order;
}

Now, when performing the JOIN operation in Supabase, we can use the UserOrder interface to properly type the response:


const { data, error } = await supabase
  .from('users')
  .select('*, orders(*)')
  .join('orders', { 'users.id': 'orders.userId' });
  
if (error) {
  console.error(error);
  return;
}

const userOrders: UserOrder[] = data;

In the above code snippet, we are using the select method to fetch all columns from the users table and the orders table. The join method is used to perform the JOIN operation based on the related column between the two tables. Finally, we assign the response data to the userOrders variable, which is of type UserOrder[].

Solution 2: Using Type Assertions

Another way to type Supabase responses when using JOIN operations is by using type assertions. Type assertions allow you to explicitly tell TypeScript the type of a value, overriding its inference.

Instead of using interfaces, we can directly assert the type of the response data:


const { data, error } = await supabase
  .from('users')
  .select('*, orders(*)')
  .join('orders', { 'users.id': 'orders.userId' });
  
if (error) {
  console.error(error);
  return;
}

const userOrders = data as UserOrder[];

In the above code snippet, we are using the as keyword to assert the type of the data variable as UserOrder[]. This tells TypeScript that the value of data should be treated as an array of UserOrder objects.

Conclusion

When using JOIN operations in Supabase with TypeScript, it is important to properly type the response data to ensure type safety and avoid potential runtime errors. In this blog post, we explored two solutions for typing Supabase responses when using JOIN operations: using interfaces and using type assertions. Both approaches provide a way to accurately represent the structure of the joined data and enable TypeScript to perform static type checking.

By following these solutions, you can ensure that your Supabase responses are properly typed and leverage the full power of TypeScript in your application.

How to Properly Type Supabase Responses When Using JOIN Operations in TypeScript?