How to delete a table with relationships in GORM?

In GORM database operations, there are several key steps to consider when deleting related tables, and the specific methods may vary depending on your requirements (e.g., cascading deletion or deleting specific entries in the child table).

1. Deleting Entries in the Child Table

If you want to delete specific entries in the child table without deleting entries in the parent table, you can use the following approach:

go
db.Model(&parentTableModel{}).Association("associationFieldName").Delete(&childTableModelInstancesToBeDeleted)

This operation does not affect entries in the parent table; it only removes the specified entries in the child table.

Example:

Assume you have User and Order models, where one user can have multiple orders. Now, we want to delete a specific order for a user:

go
var user User
db.Preload("Orders").First(&user, userId)

// Assume we want to delete the first order of the user
if len(user.Orders) > 0 {
    db.Model(&user).Association("Orders").Delete(user.Orders[0])
}

2. Cascading Deletion

When you want to delete a record and also remove all related associated records, you can use the OnDelete constraint set to CASCADE in the model definition. This ensures that when deleting an entry in the parent table, all related child table entries are automatically deleted.

Example:

When defining the model, apply OnDelete("CASCADE") to the association field:

go
type User struct {
    gorm.Model
    Orders []Order `gorm:"constraint:OnDelete:CASCADE;"`
}

type Order struct {
    gorm.Model
    UserID uint
}

Then, when you delete a user, all orders belonging to that user are automatically deleted:

go
var user User
db.First(&user, userId)
db.Delete(&user)

Conclusion

The choice of deletion method depends on your specific requirements, whether you need to retain parent table data, and whether cascading deletion of associated data is necessary. In practical applications, these operations can significantly impact data integrity and business logic, so you must exercise caution to ensure they align with your business rules.