Replace a Contract and Keep its History With Grafting

In this guide, you will learn how to build and deploy new subgraphs by grafting existing subgraphs.

Grafting reuses the data from an existing subgraph and starts indexing it at a later block. This is useful during development to get past simple errors in the mappings quickly or to temporarily get an existing subgraph working again after it has failed. Also, it can be used when adding a feature to a subgraph that takes long to index from scratch.

The grafted subgraph can use a GraphQL schema that is not identical to the one of the base subgraph, but merely compatible with it. It has to be a valid subgraph schema in its own right, but may deviate from the base subgraph's schema in the following ways:

• It adds or removes entity types
• It removes attributes from entity types
• It adds nullable attributes to entity types
• It turns non-nullable attributes into nullable attributes
• It adds values to enums
• It adds or removes interfaces
• It changes for which entity types an interface is implemented

For more information, you can check:

• Grafting

In this tutorial, we will be covering a basic usecase. We will replace an existing contract with an identical contract (with a new address, but the same code). Then, graft the existing subgraph onto the "base" subgraph that tracks the new contract.

Grafting is a powerful feature that allows you to "graft" one subgraph onto another, effectively transferring historical data from the existing subgraph to a new version. While this is an effective way to preserve data and save time on indexing, grafting may introduce complexities and potential issues when migrating from a hosted environment to the decentralized network. It is not possible to graft a subgraph from The Graph Network back to the hosted service or Subgraph Studio.

Initial Migration: when you first deploy your subgraph to the decentralized network, do so without grafting. Ensure that the subgraph is stable and functioning as expected.

Subsequent Updates: once your subgraph is live and stable on the decentralized network, you may use grafting for future versions to make the transition smoother and to preserve historical data.

By adhering to these guidelines, you minimize risks and ensure a smoother migration process.

Building subgraphs is an essential part of The Graph, described more in depth here. To be able to build and deploy the existing subgraph used in this tutorial, the following repo is provided:

• Subgraph example repo

The subgraph manifest subgraph.yaml identifies the data sources for the subgraph, the triggers of interest, and the functions that should be run in response to those triggers. See below for an example subgraph manifest that you will use:

specVersion: 0.0.4
schema:
  file: ./schema.graphql
dataSources:
  - kind: ethereum
    name: Lock
    network: goerli
    source:
      address: '0x4Ed995e775D3629b0566D2279f058729Ae6EA493'
      abi: Lock
      startBlock: 7674603
    mapping:
      kind: ethereum/events
      apiVersion: 0.0.6
      language: wasm/assemblyscript
      entities:
        - Withdrawal
      abis:
        - name: Lock
          file: ./abis/Lock.json
      eventHandlers:
        - event: Withdrawal(uint256,uint256)
          handler: handleWithdrawal
      file: ./src/lock.ts

• The Lock data source is the abi and contract address we will get when we compile and deploy the contract
• The network should correspond to a indexed network being queried. Since we're running on Goerli testnet, the network is goerli
• The mapping section defines the triggers of interest and the functions that should be run in response to those triggers. In this case, we are listening for the Withdrawal event and calling the handleWithdrawal function when it is emitted.

Grafting requires adding two new items to the original subgraph manifest:

---
features:
  - grafting # feature name
graft:
  base: Qm... # subgraph ID of base subgraph
  block: 1502122 # block number

• features: is a list of all used feature names.
• graft: is a map of the base subgraph and the block to graft on to. The block is the block number to start indexing from. The Graph will copy the data of the base subgraph up to and including the given block and then continue indexing the new subgraph from that block on.

The base and block values can be found by deploying two subgraphs: one for the base indexing and one with grafting

1. Go to The Graph Studio UI and create a subgraph on Goerli testnet called graft-example
2. Follow the directions in the AUTH & DEPLOY section on your subgraph page in the graft-example folder from the repo
3. Once finished, verify the subgraph is indexing properly. If you run the following command in The Graph Playground

{
  withdrawals(first: 5) {
    id
    amount
    when
  }
}

It returns something like this:

{
  "data": {
    "withdrawals": [
      {
        "id": "0x13098b538a61837e9f29b32fb40527bbbe63c9120c250242b02b69bb42c287e5-5",
        "amount": "0",
        "when": "1664367528"
      },
      {
        "id": "0x800c92fcc0edbd26f74e19ad058c62008a47c7789f2064023b987028343dd498-3",
        "amount": "0",
        "when": "1664367648"
      }
    ]
  }
}

Once you have verified the subgraph is indexing properly, you can quickly update the subgraph with grafting.

The graft replacement subgraph.yaml will have a new contract address. This could happen when you update your dapp, redeploy a contract, etc.

1. Go to The Graph Studio UI and create a subgraph on Goerli testnet called graft-replacement
2. Create a new manifest. The subgraph.yaml for graph-replacement contains a different contract address and new information about how it should graft. These are the block of the last event emitted you care about by the old contract and the base of the old subgraph. The base subgraph ID is the Deployment ID of your original graph-example subgraph. You can find this in The Graph Studio UI.
3. Follow the directions in the AUTH & DEPLOY section on your subgraph page in the graft-replacement folder from the repo
4. Once finished, verify the subgraph is indexing properly. If you run the following command in The Graph Playground

{
  withdrawals(first: 5) {
    id
    amount
    when
  }
}

It should return the following:

{
  "data": {
    "withdrawals": [
      {
        "id": "0x13098b538a61837e9f29b32fb40527bbbe63c9120c250242b02b69bb42c287e5-5",
        "amount": "0",
        "when": "1664367528"
      },
      {
        "id": "0x800c92fcc0edbd26f74e19ad058c62008a47c7789f2064023b987028343dd498-3",
        "amount": "0",
        "when": "1664367648"
      },
      {
        "id": "0xb4010e4c76f86762beb997a13cf020231778eaf7c64fa3b7794971a5e6b343d3-22",
        "amount": "0",
        "when": "1664371512"
      }
    ]
  }
}

You can see that the graft-replacement subgraph is indexing from older graph-example data and newer data from the new contract address. The original contract emitted two Withdrawal events, Event 1 and Event 2. The new contract emitted one Withdrawal after, Event 3. The two previously indexed transactions (Event 1 and 2) and the new transaction (Event 3) were combined together in the graft-replacement subgraph.

Congrats! You have successfully grafted a subgraph onto another subgraph.

If you want more experience with grafting, here's a few examples for popular contracts:

• Curve
• ERC-721
• Uniswap,

To become even more of a Graph expert, consider learning about other ways to handle changes in underlying datasources. Alternatives like Data Source Templates can achieve similar results