ERROR: null value in column 'created_at' of relation 'blogs' violates not-null constraint (ActiveRecord::NotNullViolation)

refer: https://www.grepper.com/tpc/null+value+in+column+%22%22modified_by%22%22+violates+not-null+constraint

解决：

ALTER TABLE <your-table> ALTER COLUMN <your-column> DROP NOT NULL;

把表的not null删除

ALTER TABLE blogs ALTER COLUMN created_at DROP NOT NULL;