❗ Foreign Key Constraint Error While Deleting User (Laravel & MySQL)
I’m encountering a foreign key constraint issue when attempting to delete a record from the users table.
🔴 Error from Laravel
Integrity constraint violation: 1451 Cannot delete or update a parent row:
a foreign key constraint fails
(erp_25_test.class_teachers,
CONSTRAINT class_teachers_teacher_id_foreign
FOREIGN KEY (teacher_id) REFERENCES users (id) ON DELETE CASCADE)
(Connection: mysql, SQL: delete from users where id = 39)
🔴 Error from phpMyAdmin
#1451 - Cannot delete or update a parent row:
a foreign key constraint fails
(erp_25_test.class_teachers,
CONSTRAINT class_teachers_teacher_id_foreign
FOREIGN KEY (teacher_id) REFERENCES users (id) ON DELETE CASCADE)
📊 Table Structure (class_teachers)
CREATE TABLE class_teachers (
id bigint(20) unsigned NOT NULL AUTO_INCREMENT,
class_section_id bigint(20) unsigned NOT NULL,
teacher_id bigint(20) unsigned NOT NULL COMMENT 'user_id',
school_id bigint(20) unsigned NOT NULL,
created_at timestamp NULL DEFAULT NULL,
updated_at timestamp NULL DEFAULT NULL,
session_year_id bigint(20) unsigned DEFAULT NULL,
PRIMARY KEY (id),
UNIQUE KEY unique_id (class_section_id,teacher_id,session_year_id),
KEY class_teachers_school_id_foreign (school_id),
KEY class_teachers_session_year_id_foreign (session_year_id),
CONSTRAINT class_teachers_class_section_id_foreign
FOREIGN KEY (class_section_id) REFERENCES class_sections (id) ON DELETE CASCADE,
CONSTRAINT class_teachers_school_id_foreign
FOREIGN KEY (school_id) REFERENCES schools (id) ON DELETE CASCADE,
CONSTRAINT class_teachers_session_year_id_foreign
FOREIGN KEY (session_year_id) REFERENCES session_years (id) ON DELETE CASCADE,
CONSTRAINT class_teachers_teacher_id_foreign
FOREIGN KEY (teacher_id) REFERENCES users (id) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
🤔 Problem Summary
The class_teachers.teacher_id column has a foreign key constraint referencing users.id with ON DELETE CASCADE.
Despite this, deleting a user (id = 39) fails with a constraint violation.
The expected behavior is that related records in class_teachers should be automatically deleted.
❓ Question
Why does the delete operation still fail even though ON DELETE CASCADE is defined, and how can this be resolved?
🔍 Additional Observation
When I export the database and then re-import it, the issue is automatically resolved.
but why not working at initially?
