## How to Reconstruct a Uniswap v4 PoolKey from a PoolId In Uniswap v4, the `PoolId` is a compressed hash derived from a `PoolKey` struct. While this design is efficient for on-chain operations, it presents a challenge: you cannot reverse the hash to recover the original `PoolKey` components. This lesson will guide you through a practical, event-based method to reconstruct a `PoolKey` when all you have is the `PoolId`. ### The Core Concept: Finding Data in On-Chain Events The key to reconstructing a `PoolKey` lies in understanding how pools are created. The individual components of a `PoolKey`—such as token addresses, fee tier, tick spacing, and hooks—are not stored on-chain in a way that is directly queryable using the `PoolId`. However, this data is not lost; it is broadcast publicly in an event at the moment of the pool's creation. When a new liquidity pool is created in Uniswap v4, the `initialize` function within the `PoolManager.sol` contract is called. A critical action performed by this function is emitting an `Initialize` event. This event contains all the data required to build the original `PoolKey`. As seen in the `PoolManager.sol` contract, the event is emitted with all the necessary details: ```solidity // Inside PoolManager.sol -> function initialize(...) // ... logic to calculate PoolId and initialize the pool ... emit Initialize(id, key.currency0, key.currency1, key.fee, key.tickSpacing, key.hooks, sqrtPriceX96, tick); key.hooks.afterInitialize(key, sqrtPriceX96, tick); ``` This `Initialize` event log is a public record on the blockchain and includes: - `id`: The `PoolId` of the newly created pool. - `key.currency0`: The address of the first token. - `key.currency1`: The address of the second token. - `key.fee`: The pool's fee tier. - `key.tickSpacing`: The designated tick spacing. - `key.hooks`: The address of the pool's hooks contract (or `address(0)` if none). By finding the specific `Initialize` event that corresponds to your `PoolId`, you can retrieve all the components needed to reconstruct the `PoolKey`. ### The Recommended Method: Querying with Dune Analytics While you could write a custom script to scan the blockchain for this event, a far simpler and more efficient method is to use Dune Analytics. Dune is a powerful platform that indexes blockchain data, making it easily searchable through standard SQL queries. The platform has already indexed the `Initialize` events from the Uniswap v4 contracts. To find the data for a specific `PoolId`, you can run a simple SQL query. This query targets the table containing all `Initialize` events and filters it to find the one matching your `PoolId`. Here is the example query: ```sql select * from uniswap_v4_ethereum.poolmanager_evt_initialize where id = 0x3ea74c37fbb79dfcd6d760870f0f4e00cf4c3960b3259d0d43f211c0547394c1 ``` Let's break this down: - `select * from uniswap_v4_ethereum.poolmanager_evt_initialize`: This command selects all columns from the Dune table that stores the `Initialize` event data from the Uniswap v4 `PoolManager` contract on the Ethereum network. - `where id = ...`: This clause filters the millions of events to return only the single row where the `id` column matches the `PoolId` you provide. Running this query on Dune will return a single result containing the `currency0`, `currency1`, `fee`, `tickSpacing`, and `hooks` values for your pool. ### How to Find a Pool's `PoolId` Before you can query Dune, you first need a `PoolId`. The easiest way to find one is by using the Uniswap user interface. Let's find the `PoolId` for the ETH / USDC pool on Ethereum as an example: 1. Navigate to the Uniswap web application. 2. Select the **Explore** tab to view pools. 3. Use the filters to specify **Protocol: `v4`** and **Network: `Ethereum`**. 4. From the list of available pools, click on the one you are interested in (e.g., `ETH / USDC`). 5. On the pool's detail page, locate the pool's name at the top (e.g., `ETH / USDC`). 6. Hover your cursor over the name, and a copy icon will appear. 7. Click the icon to copy the `PoolId` to your clipboard. With the `PoolId` copied, you can now return to Dune Analytics, paste it into the `where id = ` clause of the SQL query, and run it. The query result will provide you with the complete set of data required to fully reconstruct that pool's `PoolKey`.