# Open By Collateral

Continuing from [/pages/MhRivYPoISvgsUgYmF2I#id-4.-select-an-use-case](https://docs.protocolink.com/lending-sdk/sdk/pages/MhRivYPoISvgsUgYmF2I#id-4.-select-an-use-case "mention").

Open By Collateral enables users to achieve the desired collateral exposure in a single step by using a flash loan.

* Zap token: the user-provided token to be swapped to the collateral token.
* Collateral token: the collateral token to be leveraged.
* Debt token: the debt token to be leveraged against.

## 5. Preview the estimated post-open portfolio

By specifying the zap token, the zap token amount, the collateral token, the collateral token amount, and the debt token, the function will return the borrowed debt token amount, the updated user portfolio, and the logics to be executed.

```typescript
// User obtains a quotation for opening by collateral
const zapToken = mainnetTokens.USDC;
const zapAmount = '1000';
const collateralToken = mainnetTokens.WETH;
const collateralAmount = '1';
const debtToken = mainnetTokens.USDC;
const openByCollateralInfo = await adapter.openByCollateral({
  account,
  portfolio,
  zapToken,
  zapAmount,
  collateralToken,
  collateralAmount,
  debtToken
});
```

The logics should include:

1. Swap the zap token for the collateral token
2. Borrow a flash loan of the debt token
3. Swap the debt token for the collateral token
4. Deposit the collateral token and get the protocol token (aToken)
5. Return the protocol token (aToken) to the user
6. Borrow the debt token
7. Repay the flash loan with the debt token

## 6. Obtain the required approval permission and send the router transaction

To perform the logics, certain approvals need to be processed. You may refer to [Estimate Router Data](/protocolink-sdk/estimate-router-data.md) and [Send Router Transaction](/protocolink-sdk/send-router-transaction.md) for more details.

```typescript
// User needs to permit the Protocolink user agent to borrow for the user
const estimateResult = await apisdk.estimateRouterData(
  { chainId, account, logics: openByCollateralInfo.logics }
);

// User obtains an open-by-collateral transaction request
const routerData: apisdk.RouterData = {
  chainId,
  account,
  logics: openByCollateralInfo.logics
};
const transactionRequest = await apisdk.buildRouterTransactionRequest(routerData);
```


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