---
id: upgrade
title: Updating Contracts
---

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NEAR accounts separate their logic (contract's code) from their state (storage), allowing the code to be changed.

Contract's can be updated in two ways:

1. **Through tools** such as [NEAR CLI](../../../4.tools/cli.md) or [near-api-js](../../../4.tools/near-api-js/quick-reference.md) (if you hold the account's [full access key](../../../1.concepts/protocol/access-keys.md)).
2. **Programmatically**, by implementing a method that [takes the new code and deploys it](#programmatic-update).

---

## Updating Through Tools

Simply re-deploy another contract using your preferred tool, for example, using [NEAR CLI](../../../4.tools/cli.md):

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  <TabItem value="near-cli">

```bash
# (optional) If you don't have an account, create one
near create-account <account-id> --useFaucet

# Deploy the contract
near deploy <account-id> <wasm-file>
```

</TabItem>

<TabItem value="near-cli-rs">

```bash
# (optional) If you don't have an account, create one
near account create-account sponsor-by-faucet-service somrnd.testnet autogenerate-new-keypair save-to-keychain network-config testnet create

# Deploy the contract
near contract deploy <accountId> use-file <route_to_wasm> without-init-call network-config testnet sign-with-keychain send
```

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</Tabs>

---

## Programmatic Update
A smart contract can also update itself by implementing a method that:
1. Takes the new wasm contract as input
2. Creates a Promise to deploy it on itself

<CodeTabs>
  <Language value="rust" language="rust">
    <Github fname="update.rs"
        url="https://github.com/near-examples/update-migrate-rust/blob/main/self-updates/base/src/update.rs"
        start="10" end="31" />

</Language>

</CodeTabs>

#### How to Invoke Such Method?

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```bash
# Load the contract's raw bytes
CONTRACT_BYTES=`cat ./path/to/wasm.wasm | base64`

# Call the update_contract method
near call <contract-account> update_contract "$CONTRACT_BYTES" --base64 --accountId <manager-account> --gas 300000000000000
```

</TabItem>

<TabItem value="near-cli-rs">

```bash
# Call the update_contract method
near contract call-function as-transaction <contract-account> update_contract file-args </path/to/wasm.wasm> prepaid-gas '300.0 Tgas' attached-deposit '0 NEAR' sign-as <manager-account> network-config testnet sign-with-keychain send
```

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<TabItem value="js" label="🌐 JavaScript">

```js
// Load the contract's raw bytes
const code = fs.readFileSync("./path/to/wasm.wasm");

// Call the update_contract method
await wallet.callMethod({contractId: guestBook, method: "update_contract", args: code, gas: "300000000000000"});
```

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</Tabs>

:::tip DAO Factories

This is how DAO factories [update their contracts](https://github.com/near-daos/sputnik-dao-contract/blob/main/sputnikdao-factory2/src/factory_manager.rs#L60)

:::

---

## Migrating the State

Since the account's logic (smart contract) is separated from the account's state (storage),
**the account's state persists** when re-deploying a contract.

Because of this, **adding methods** or **modifying existing ones** will yield **no problems**.

However, deploying a contract that **modifies or removes structures**  stored in the state will raise an
error: `Cannot deserialize the contract state`, in which case you can choose to:
1. Use a different account
2. Rollback to the previous contract code
3. Add a method to migrate the contract's state

<hr className="subsection" />

### The Migration Method

If you have no option but to migrate the state, then you need to implement a method that:
1. Reads the current state of the contract
2. Applies different functions to transform it into the new state
3. Returns the new state

:::tip DAO Update

This is how DAOs [update themselves](https://github.com/near-daos/sputnik-dao-contract/blob/main/sputnikdao2/src/upgrade.rs#L59)

:::

<hr className="subsection" />

### Example: Guest Book Migration

Imagine you have a Guest Book where you store messages, and the users can pay for such messages
to be "premium". You keep track of the messages and payments using the following state:

<CodeTabs>
  <Language value="rust" language="rust">
    <Github fname="lib.rs"
        url="https://github.com/near-examples/update-migrate-rust/blob/main/basic-updates/base/src/lib.rs"
        start="10" end="21" />        

</Language>

</CodeTabs>

#### Update Contract

At some point you realize that you could keep track of the `payments` inside of the `PostedMessage` itself,
so you change the contract to:

<CodeTabs>
  <Language value="rust" language="rust">
    <Github fname="lib.rs"
        url="https://github.com/near-examples/update-migrate-rust/blob/main/basic-updates/update/src/lib.rs"
        start="12" end="23" />        

</Language>

</CodeTabs>

#### Incompatible States

If you deploy the update into an initialized account the contract will fail to deserialize the account's state,
because:
1. There is an extra `payments` vector saved in the state (from the previous contract)
2. The stored `PostedMessages` are missing the `payment` field (as in the previous contract)

#### Migrating the State

To fix the problem, you need to implement a method that goes through the old state, removes the `payments` vector and
adds the information to the `PostedMessages`:

<CodeTabs>
  <Language value="rust" language="rust">
    <Github fname="lib.rs"
        url="https://github.com/near-examples/update-migrate-rust/blob/main/basic-updates/update/src/migrate.rs"
        start="3" end="46" />

</Language>

</CodeTabs>

Notice that `migrate` is actually an [initialization method](../anatomy/anatomy.md#initialization-method) that **ignores** the existing state (`[#init(ignore_state)]`), thus being able to execute and rewrite the state.

:::tip

You can follow a migration step by step in the [official migration example](https://github.com/near-examples/update-migrate-rust/tree/main/basic-updates/base)

:::