Resolving Sequelize Migration Error: Cannot read property 'toString' of undefined

Learn how to fix the `Cannot read property 'toString' of undefined` error in your Sequelize migration by understanding common issues related to data types.
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This video is based on the question https://stackoverflow.com/q/66510955/ asked by the user 'Sean D' ( https://stackoverflow.com/u/7608946/ ) and on the answer https://stackoverflow.com/a/66511846/ provided by the user 'Wang Liang' ( https://stackoverflow.com/u/11343720/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting Sequelize Migration: Fixing the Cannot read property 'toString' of undefined Error

If you've encountered the error message ERROR: Cannot read property 'toString' of undefined while running a Sequelize migration, you're not alone. This issue can arise during the process of modifying database schemas in Node.js applications using Sequelize ORM. Understanding the cause and solution for this error can prove essential in ensuring your migrations run smoothly.

Understanding the Problem

The migration script you are running involves adding a new column to your Documents table. The error indicates that there may be an issue with the way data types are being referenced in your Sequelize migration. The following line of code is particularly suspect:

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In Sequelize, the data types must be referenced correctly to prevent errors during migrations. If a wrong property or value is used, it can lead to the toString error.

Solution Overview

To troubleshoot and resolve this issue, let's take the following steps:

Correct the Data Type Referencing

Modify Your Model Definitions

Double-Check Migration Logic

1. Correct the Data Type Referencing

In your migration file, replace DataTypes.String with DataTypes.STRING. This capitalization is crucial because JavaScript is case-sensitive:

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

2. Modify Your Model Definitions

You will also need to apply a similar correction in your Document model file. Change all occurrences of DataTypes.String to DataTypes.STRING and DataTypes.number to DataTypes.NUMBER:

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3. Double-Check Migration Logic

After making the necessary changes to your migration script and model, run the migration command again:

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

Be sure to check for any dependency issues, including ensuring your version of Sequelize, PostgreSQL, and Node.js are compatible. The version numbers seen in your initial setup:

Node: 14.15.4

PostgreSQL: 12.6

Sequelize: 6.5.0

Sequelize CLI: 6.2.0

Make sure that these align with your project requirements.

Conclusion

By correcting the capitalization in your data type references, you eliminate the potential for the Cannot read property 'toString' of undefined error. Always be meticulous about case sensitivity in JavaScript, especially when working with libraries like Sequelize. If you continue to encounter issues, double-check your migration logic and consult the Sequelize documentation for further assistance.

Remember, taking the time to understand potential errors can save you from unnecessary headaches in the future. Happy coding!