Скачать или смотреть Resolving the errno: 150 "Foreign key constraint is incorrectly formed" Error in Laravel 7

A comprehensive guide to fixing foreign key errors in Laravel while creating tables, specifically focusing on the `errno: 150` issue.
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This video is based on the question https://stackoverflow.com/q/63960632/ asked by the user 'Illyrian' ( https://stackoverflow.com/u/10918620/ ) and on the answer https://stackoverflow.com/a/63960925/ provided by the user 'Illyrian' ( https://stackoverflow.com/u/10918620/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the errno: 150 "Foreign key constraint is incorrectly formed" Error in Laravel 7

If you've encountered the dreaded errno: 150 "Foreign key constraint is incorrectly formed" error message while working with Laravel 7, you're not alone. This issue often arises when trying to establish foreign key constraints between tables in your MySQL database. In this guide, we'll explore the common causes of this error and provide a step-by-step guide to fixing it.

Understanding the Problem

The error occurs during the creation of a table, wherein you attempt to set up foreign key constraints that MySQL cannot process due to several potential reasons. Let’s take a closer look at some of the most common causes:

Data Type Mismatch: The data types of the foreign key column and the referenced primary key column should match.

Incorrect Reference Table or Column: Ensure that the table and column names referenced in the foreign key constraints are correct.

Unsigned vs. Signed Columns: Foreign keys referencing unsigned columns must themselves be unsigned.

Table Existence: Foreign key constraints can only be established if the referenced table exists at the time of the creation.

Step-by-Step Solution

Let's fix the error showcased in the example from the question. Here’s how you can address the issues in the clothes table creation code:

Step 1: Create Tables in Proper Order

Before creating the clothes table, ensure that all referenced tables—bands, category, gender, and colors—are created first. Here’s how the creation of these tables would ideally look:

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

Step 2: Correctly Define Foreign Keys in the clothes Table

Now that we have the necessary tables, we can safely create the clothes table. Be cautious with the foreign key definitions. Here's how the corrected creation code looks:

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

Step 3: Testing the Migration

After making these changes, try running your migration again. If everything is set up correctly, the migration should execute without any errors.

Key Takeaways

Always create referenced tables before the table that includes foreign keys.

Ensure the foreign key and referenced key data types match.

Pay attention to whether columns are signed or unsigned.

By following these steps and understanding the underlying issues, you can easily resolve errno: 150 errors in your Laravel 7 applications. Happy coding!