Retrieve all rows from the database using FastAPI and SQLModel

Learn how to effectively fetch all items from your Postgres database using FastAPI and SQLModel while understanding common pitfalls.
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Retrieve All Rows from the Database using FastAPI and SQLModel: A Simple Guide

When developing applications with FastAPI, you might encounter scenarios where you need to retrieve data from your database, such as fetching all Item rows from a Postgres database. If you've tried to implement this functionality and ran into an error, don't worry! In this post, we’ll troubleshoot the problems you've encountered and provide a clear, organized solution.

Understanding the Problem

The goal here is simple: create a GET endpoint in your FastAPI application that retrieves all items from your database. However, a common error might occur along the way—specifically a TypeError stating: 'SQLModelMetaclass' object is not iterable. To troubleshoot this problem, let's first look at the model definitions you have along with the CRUD operations implemented.

Models Defined

You have several models defined using SQLModel as follows:

ItemDb

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GadgetDb

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The Placeholder Model

You also defined a model for item retrieval but made a mistake:

[[See Video to Reveal this Text or Code Snippet]]

The Item class is not an ORM model because it lacks the table=True attribute. This is crucial when interacting with the database.

The Solution

Now that we’ve identified the core issue, let’s explore how to resolve it. The primary step is to utilize the correct model when querying the database.

Steps to Fix the Issue

Use the Correct Model: Instead of using your Item class in database queries, change it to refer to ItemDb, which is properly defined as an ORM model with table=True.

Update Your CRUD Function: Modify your CRUD function to ensure it queries the correct model type.

Here’s how you can revise your function to fetch all items correctly:

[[See Video to Reveal this Text or Code Snippet]]

Adjust Your Endpoint Function: Next, update your endpoint to return the correct model type:

[[See Video to Reveal this Text or Code Snippet]]

Test Your Endpoint: Once you make these adjustments, test the /api/v1/items/ endpoint to ensure it returns all the items as expected. You should no longer see the type error, and instead receive a list of items.

Conclusion

By ensuring that your queries use the correct ORM models, you can effectively interact with your database without running into common type errors. The key takeaway is that when using FastAPI and SQLModel, always double-check that your models are properly defined for ORM usage, especially in CRUD operations.

Implement these changes, and you should have a fully functional route for retrieving items from your Postgres database. Happy coding!