Week 5 (Blockchain track): Guided build#

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See also

Full context: root README, Week 5.

Goal#

A real Solidity contract, common failure modes at a conceptual level, and a first, still-scaffolded transaction sent from Python. Instructions are still fairly step-by-step.

Scope#

  • A Solidity contract beyond the trivial one from Week 4: state, access control, events.
  • Common failure modes at a conceptual level (reentrancy, overflow, access control), before writing anything complex, so security is a habit, not an afterthought.
  • With the contract deployed, send it a basic transaction and read its state back from a Python script, to confirm it actually works before automation enters the picture in Week 6.

The project: AssetRegistry#

Weeks 5, 6, and 7 build one project, not three. The contract you write and deploy this week, AssetRegistry, is the same contract the Week 6 backend service signs transactions against and the same contract the Week 7 service adds a second event handler and a test suite for. By the time you reach the Week 8 capstone, especially the acceptance gate, you will already have hands-on experience with exactly the shape of data that spec asks you to reason about: a holder's eligibility, a holder's balance (a size limit lives right next to it), and a timestamp of when that record last changed (a stand-in for "how fresh is the evidence backing this").

AssetRegistry is a deliberately small registry contract. It tracks, per address:

  • whether that address is a registered holder at all,
  • whether it is currently eligible to hold the asset,
  • its current balance, and
  • when that record was last touched.

Only the contract's owner (whoever deployed it, standing in for "our backend service") can register a holder or change any of those fields. Every change emits an event. That's the whole contract. It's small on purpose: the point of Weeks 5-7 is not "write a bigger contract," it's "build the off-chain muscle (transactions, managed keys, event handling, idempotency) that any real integration needs," and a small, well-understood contract is the right training weight for that.

Do this in order#

Steps 1-4 are required. Step 5 is optional; skipping it leaves no gap in what Week 6 assumes you know.

  1. notes/01-state-and-storage.md through 05-organizing-a-walkthrough-script.md, in order.
  2. exercises/00-guided-write-assetregistry.md, a line-by-line guided build of the contract's genuinely new pieces (struct, mapping, access-control modifier), compiling after every step.
  3. exercises/01-read-and-predict.md, six short Solidity snippets to read and predict, two per failure mode.
  4. project/README.md's full walkthrough: deploy with Ape, export the ABI, run interact.py.
  5. Optional: exercises/02-guided-write-creditledger.md, a second, smaller guided build isolating just mapping-plus-access-check, useful if that combination didn't fully click the first time; and project/README.md's two stretch goals (an aggregate read function, a fourth event) for more reps against this exact contract.