State invariants before an update
See this course’s project requirements
A local SQLite seat-transfer exercise with before/after totals, an all-or-nothing update, a deliberately rejected change and rollback evidence.
Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.
What to include
- A seat-transfer contract with total 10 preserved.
- Two targeted updates with a declared completion boundary.
- A committed all-or-nothing transfer record.
- A 5, B 5 and no active transaction after rejection.
- A parameterized update/lookup record with known-ID validation.
- A checked seat-transfer transaction packet.
Review and revise
Use these criteria to check your work and choose what to improve.
- The implementation or declared simulation follows the supplied contract and retains inspectable original inputs.
- Normal, boundary and rejected cases are recorded with expected versus observed results.
- The changed case has a correct explanation and does not rely on hidden state.
- The project includes source, outputs, instructions and honest tool, privacy and verification limits.
Want more background?
The idea in everyday life
Fictional groups have A 8 seats and B 2 seats, total 10. Transfer 3 from A to B should produce A 5, B 5.
An update is safe for a declared purpose only if it preserves that rule. Seat transfer changes distribution, not grand total; negative group quantities and unknown recipient IDs are forbidden.
State invariants before an update — original worked practice
An update is safe for a declared purpose only if it preserves that rule. Seat transfer changes distribution, not grand total; negative group quantities and unknown recipient IDs are forbidden.
Fictional groups have A 8 seats and B 2 seats, total 10. Transfer 3 from A to B should produce A 5, B 5.
1. Step 1
Write the baseline quantities and sum.
You should see: 8+2=10 seats.
This keeps the rule and its observable result together.
2. Step 2
Subtract 3 from A and add 3 to B.
You should see: A 5, B 5 still total 10.
This keeps the rule and its observable result together.
3. Step 3
State quantity>=0 and known-group requirements.
You should see: A transfer cannot create a deficit or an unknown recipient.
This keeps the rule and its observable result together.
4. Step 4
Build a before/after invariant table.
You should see: A seat-transfer contract with total 10 preserved.
This keeps the rule and its observable result together.
What to finish
A seat-transfer contract with total 10 preserved.
Watch for this
Applying the paired updates without retaining the total quantity invariant.
How can I tell I understand it?
Explain and demonstrate the required distinction: An update is safe for a declared purpose only if it preserves that rule. Seat transfer changes distribution, not grand total; negative group quantities and unknown recipient IDs are forbidden. Show a changed input and the expected result without weakening this contract.
Quick knowledge check
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Source & access notes · checked 2026-10-01
Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.
Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.
Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.
Source & access notes · checked 2026-10-01
Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.
Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.
Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.
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