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Resolving the None Value Issue in Pydantic Models

Learn how to fix the `None` value issue in your Pydantic models by properly using field aliases for enhanced functionality. --- This video is based on the question https://stackoverflow.com/q/77251836/ asked by the user 'Saikat Karmakar' ( https://stackoverflow.com/u/9805823/ ) and on the answer https://stackoverflow.com/a/77632790/ provided by the user 'forgotten dinosaur' ( https://stackoverflow.com/u/23071191/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, comments, revision history etc. For example, the original title of the Question was: Wrong filed value in pydantic model Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Understanding the None Value Issue in Pydantic Models When working with Pydantic, a data validation and settings management library in Python, users may encounter scenarios where fields unexpectedly return a None value. This often leads to confusion, especially for those who rely on these models for data integrity in their applications. In this guide, we'll address one such problem related to field naming and how to properly implement the alias feature in Pydantic to avoid None values. The Problem Consider the following Pydantic model class definition for uploading a result: [[See Video to Reveal this Text or Code Snippet]] When we attempt to create an instance of this model with the following call: [[See Video to Reveal this Text or Code Snippet]] We encounter an unexpected output for tag_uid, which is None: [[See Video to Reveal this Text or Code Snippet]] This occurrence is puzzling, and it raises the question: Why isn't the tag_uid field populating correctly? The Solution The issue at hand lies with how we are referencing the field in the model when initializing it. In the original model, the field is defined as tag_uid, but it has an alias of tagUid. This is crucial because when you use Pydantic with aliases, you need to call the model using the alias rather than the original field name. Steps to Fix the Issue Use the Correct Alias: To resolve the None value issue, change how you refer to the tag_uid field when creating an instance of the model. Use the alias tagUid instead of tag_uid: [[See Video to Reveal this Text or Code Snippet]] Summary of Key Points Field Naming: When using Pydantic, ensure you refer to your fields by their alias if you've defined one. Pydantic's Alias Feature: This allows for flexibility in how your data models can be defined and used, especially when dealing with JavaScript or RESTful APIs, where camelCase conventions may be prevalent. Conclusion Working with Pydantic models can greatly enhance data validation and management in Python applications. However, as illustrated in this case, attention to detail is critical. By understanding how to properly utilize field aliases, you can avoid common pitfalls such as unexpected None values in your data models. Always ensure you're using the correct names when initializing instances, and you'll find your models behaving as expected. Happy coding with Pydantic! If you have further questions or run into more issues, feel free to engage with the community or refer to the documentation!