Скачать или смотреть How to Set Default Values for Primary Columns in TypeORM with NestJS

Struggling with setting default values for primary columns in TypeORM while using NestJS? This guide provides invaluable insights to resolve common pitfalls and implement effective solutions.
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Troubleshooting Default Values for Primary Columns in TypeORM

When working with TypeORM in a NestJS application, developers often face challenges related to setting default values for primary columns. This issue can lead to frustrating error messages, such as ER_NO_DEFAULT_FOR_FIELD, if not handled correctly. In this guide, we'll explore the problem and how to effectively set up default values in your TypeORM entities.

Understanding the Problem

Imagine you have an entity named UserSession. One of the fields, sessionId, is meant to have a default value generated by a function that creates a random string. Here's the code snippet that represents the initial setup:

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When you attempt to save a new user session like this:

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You might encounter this error:

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The underlying issue is that TypeORM does not set default values at the application level but rather relies on the database's native capabilities.

Why Doesn't default Work as Expected?

You might wonder about the use of the default property within the @ PrimaryColumn() decorator. It’s important to note:

Database Level Default: The default property is utilized for creating a default value only at the database level. This means the database will assign a value to the field if one isn't provided, but this doesn't work for complex generated values.

Need for a Workaround: Simple string or number defaults work fine; however, when you need to execute a function like cryptoRandomString(), it doesn't trigger automatically when using save() with an object literal.

The Solution

To effectively manage the default values without encountering issues, you can set your entity definition like this:

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Creating a User Instance

Rather than using .save() directly with an object, use the repository’s .create() method, which neatly wraps the creation of an entity with the defined defaults:

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This approach ensures that both userId and sessionId are generated automatically when a new user is created without needing manual assignment.

Saving the User

Finally, save the user instance using the .save() method:

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Using this structured approach allows you to simplify the handling of default values and avoid complications with primary columns.

Conclusion

Setting default column values in TypeORM requires understanding its limitations, particularly with primary columns. By utilizing entity initializers combined with the .create() method, you can effectively manage default values without running into database errors.

Next time you encounter issues with default values in TypeORM, consider restructuring your entity definition as shown above. This will streamline your development process and lead to more maintainable code.