148 lines
3.6 KiB
PL/PgSQL
148 lines
3.6 KiB
PL/PgSQL
SET search_path TO lab5;
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-- TASK 1 – Enforce Section Capacity
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-- 1. Trigger function: ensure no course offering exceeds capacity
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CREATE OR REPLACE FUNCTION check_offering_capacity()
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RETURNS TRIGGER AS $$
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DECLARE
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v_capacity INTEGER;
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v_current INTEGER;
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BEGIN
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SELECT off_capacity
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INTO v_capacity
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FROM course_offering
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WHERE off_id = NEW.off_id;
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SELECT COUNT(*)
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INTO v_current
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FROM enrollment
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WHERE off_id = NEW.off_id
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AND enr_status = 'Active';
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IF v_current >= v_capacity THEN
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RAISE EXCEPTION
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'Cannot enroll student %. Section % is full (capacity=%).',
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NEW.stu_num, NEW.off_id, v_capacity;
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END IF;
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RETURN NEW;
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END;
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$$ LANGUAGE plpgsql;
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-- 2. Trigger
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CREATE OR REPLACE TRIGGER trg_check_capacity
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BEFORE INSERT ON enrollment
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FOR EACH ROW
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EXECUTE FUNCTION check_offering_capacity();
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-- TASK 2 – Enrollment Audit Logging
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CREATE TABLE IF NOT EXISTS enrollment_audit (
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audit_id SERIAL PRIMARY KEY,
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enr_id_stu VARCHAR(20),
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enr_id_off INTEGER,
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action_type VARCHAR(10),
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old_status VARCHAR(8),
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new_status VARCHAR(8),
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action_ts TIMESTAMP DEFAULT NOW(),
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action_user TEXT DEFAULT current_user
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);
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CREATE OR REPLACE FUNCTION audit_enrollment_changes()
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RETURNS TRIGGER AS $$
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BEGIN
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IF TG_OP = 'INSERT' THEN
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INSERT INTO enrollment_audit(
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enr_id_stu,
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enr_id_off,
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action_type,
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new_status
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)
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VALUES (
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NEW.stu_num,
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NEW.off_id,
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'INSERT',
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NEW.enr_status
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);
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ELSIF TG_OP = 'UPDATE' THEN
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INSERT INTO enrollment_audit(
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enr_id_stu,
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enr_id_off,
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action_type,
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old_status,
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new_status
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)
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VALUES (
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NEW.stu_num,
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NEW.off_id,
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'UPDATE',
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OLD.enr_status,
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NEW.enr_status
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);
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END IF;
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RETURN NEW;
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END;
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$$ LANGUAGE plpgsql;
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CREATE OR REPLACE TRIGGER trg_enrollment_audit
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AFTER INSERT OR UPDATE ON enrollment
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FOR EACH ROW
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EXECUTE FUNCTION audit_enrollment_changes();
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-- TASK 3 – Validate Enrollment Status
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ALTER TABLE enrollment DROP CONSTRAINT IF EXISTS enr_status_ck;
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ALTER TABLE enrollment
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ADD CONSTRAINT enr_status_ck
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CHECK (enr_status IN ('Active', 'Dropped', 'Completed', 'Failed'));
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CREATE OR REPLACE FUNCTION validate_enrollment_status()
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RETURNS TRIGGER AS $$
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BEGIN
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IF NEW.enr_status NOT IN ('Active','Dropped','Completed','Failed') THEN
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RAISE EXCEPTION 'Invalid enrollment status: %', NEW.enr_status;
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END IF;
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RETURN NEW;
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END;
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$$ LANGUAGE plpgsql;
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CREATE OR REPLACE TRIGGER trg_validate_status
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BEFORE INSERT OR UPDATE OF enr_status ON enrollment
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FOR EACH ROW
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EXECUTE FUNCTION validate_enrollment_status();
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-- TESTS
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INSERT INTO enrollment VALUES ('S100', 1, 'Active');
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INSERT INTO enrollment VALUES ('S101', 1, 'Active');
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INSERT INTO enrollment VALUES ('S102', 1, 'Active');
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INSERT INTO enrollment VALUES ('S200', 2, 'Active');
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UPDATE enrollment SET enr_status = 'Dropped'
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WHERE stu_num = 'S200' AND off_id = 2;
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UPDATE enrollment
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SET enr_status = 'Potato'
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WHERE stu_num = 'S200' AND off_id = 2;
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-- OUTPUT
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-- SELECT * FROM enrollment;
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-- SELECT * FROM enrollment_audit;
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-- REFLECTION
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-- Storing business rules directly inside the database ensures that
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-- data remains correct and consistent no matter what application
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-- or user interacts with it. Trigger-based validation centralizes
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-- logic so errors are prevented at the source instead of being caught
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-- later in the application.
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