Rapid Prototyping
When you change the interface of a contract and re-deploy it, you may see this error:
Cannot deserialize the contract state.
Why does this happen?
When your contract is executed, the NEAR Runtime reads the serialized state from disk and attempts to load it using current contract code. When your code changes but the serialized state stays the same, it can't figure out how to do this.
How can you avoid such errors?
When you're still in the Research & Development phase, building a prototype and deploying it locally or on testnet, you can just delete all previous contract state when you make a breaking change. See below for a couple ways to do this.
When you're ready to deploy a more stable contract, there are a couple of production strategies that will help you update the contract state without deleting it all. And once your contract graduates from "trusted mode" (when maintainers control a Full Access key) to community-governed mode (no more Full Access keys), you can set up your contract to upgrade itself.
Rapid Prototyping: Delete Everything All The Time
There are two ways to delete all account state:
- Deploying on a new account each time
- Deleting & recreating contract account
For both cases, let's consider the following example.
Let's say you deploy a JS status message contract contract to testnet, then call it with:
- near-cli
- near-cli-rs
near call [contract] set_status '{"message": "lol"}' --accountId you.testnet
near view [contract] get_status '{"account_id": "you.testnet"}'
near contract call-function as-transaction [contract] set_status json-args '{"message": "lol"}' prepaid-gas '30 TeraGas' attached-deposit '0 NEAR' sign-as you.testnet network-config testnet sign-with-keychain send
near contract call-function as-read-only [contract] get_status text-args '{"account_id": "you.testnet"}' network-config testnet now
This will return the message that you set with the call to set_status
, in this case "lol"
.
At this point the contract is deployed and has some state.
Now let's say you change the contract to store two kinds of data for each account, a status message and a tagline. You can add to the contract code a LookupMap
for both status message and another one for the tagline, both indexed by the account ID.
You build & deploy the contract again, thinking that maybe because the new taglines
LookupMap has the same prefix as the old records
LookupMap (the prefix is a
, set by new LookupMap("a"
), the tagline for you.testnet
should be "lol"
. But when you near view
the contract, you get the "Cannot deserialize" message. What to do?
1. Deploying on a new account each time
When first getting started with a new project, the fastest way to deploy a contract is creating an account and deploying the contract into it using NEAR CLI
.
- near-cli
- near-cli-rs
near create-account <account-id> --useFaucet
near deploy <account-id> ./path/to/compiled.wasm
near account create-account sponsor-by-faucet-service <my-new-dev-account>.testnet autogenerate-new-keypair save-to-keychain network-config testnet create
near contract deploy <my-new-dev-account>.testnet use-file <route_to_wasm> without-init-call network-config testnet sign-with-keychain
This does a few things:
- Creates a new testnet account pre-funded with 10N from the faucet
- Stores the private key for this account in the
~/.near-credentials
folder - Deploys your contract code to this account
2. Deleting & Recreating Contract Account
Another option to start from scratch is to delete the account and recreate it.
- near-cli
- near-cli-rs
near delete <accountId> <beneficiaryId>
near account delete-account app-name.you.testnet beneficiary you.testnet network-config testnet sign-with-keychain send
This sends all funds still on the <accountId>
account to <beneficiaryId>
and deletes the contract that had been deployed to it, including all contract state.
Now you create the sub-account and deploy to it again using the commands above, and it will have empty state like it did the first time you deployed it.