... so I took out the Profile model
What does "took out" mean? What exactly did you do? Is it the
exact reverse of how you created that model to start with?
ActiveRecord::InvalidForeignKey (Mysql2::Error: Cannot add or update a child
row: a foreign key constraint fails (`socialnetworking_development`.`posts`,
CONSTRAINT `fk_rails_cd61a4aa45` FOREIGN KEY (`user_id`) REFERENCES
Given that you're seeing a *database-generated* error -- have you
looked at the relationships, i.e. foreign keys, in the referenced tables
in that database?