building-a-subgraph-workshop

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The Graph - Subgraph Workshop

Learn how to build a GraphQL API on top of the Ethereum blockchain to query data from Foundation.

In this workshop you'll learn how to build and deploy a subgraph using the Foundation NFT smart contract.

Prerequisites

To be successful in this workshop, you should have Node.js installed on your machine.

Getting started

To get started, open The Graph Hosted Service and either sign in or create a new account.

Next, go to the dashboard and click on Add Subgraph to create a new subgraph.

Configure your subgraph with the following properties:

• Subgraph Name - Foundationsubgraph
• Subtitle - A subgraph for querying NFTs
• Optional - Fill the description and GITHUB URL properties

Once the subgraph is created, we will initialize the subgraph locally using the Graph CLI.

Initializing a new subgraph using the Graph CLI

Next, install the Graph CLI:

npm install -g @graphprotocol/graph-cli

# or

yarn global add @graphprotocol/graph-cli

Once the Graph CLI has been installed you can initialize a new subgraph with the Graph CLI init command.

There are two ways to initialize a new subgraph:

1 - From an example subgraph (example command, do not run)

graph init --from-example <GITHUB_USERNAME>/<SUBGRAPH_NAME> [<DIRECTORY>]

2 - From an existing smart contract (example command, do not run)

If you already have a smart contract deployed to Ethereum mainnet or one of the testnets, initializing a new subgraph from this contract is an easy way to get up and running.

graph init --from-contract <CONTRACT_ADDRESS> \
  [--network <ETHEREUM_NETWORK>] \
  [--abi <FILE>] \
  <GITHUB_USER>/<SUBGRAPH_NAME> [<DIRECTORY>]

In our case we'll be starting with the Foundation proxy contract so we can initialize from that contract address by passing in the contract address using the --from-contract flag.

Run the following command:

graph init --from-contract 0xc9fe4ffc4be41d93a1a7189975cd360504ee361a --protocol ethereum \
--network mainnet --contract-name Token --index-events

? Product for which to initialize › hosted-service
? Subgraph name › your-username/Foundationsubgraph
? Directory to create the subgraph in › Foundationsubgraph
? Ethereum network › Mainnet
? Contract address › 0xc9fe4ffc4be41d93a1a7189975cd360504ee361a
? Contract Name · Token

This command will generate a basic subgraph based off of the contract address passed in as the argument to --from-contract. By using this contract address, the CLI will initialize a few things in your project to get you started (including fetching the abis and saving them in the abis directory).

By passing in --index-events the CLI will automatically populate some code for us both in schema.graphql as well as src/mapping.ts based on the events emitted from the contract.

The main configuration and definition for the subgraph lives in the subgraph.yaml file. The subgraph codebase consists of a few files:

• subgraph.yaml: a YAML file containing the subgraph manifest
• schema.graphql: a GraphQL schema that defines what data is stored for your subgraph, and how to query it via GraphQL
• AssemblyScript Mappings: AssemblyScript code that translates from the event data in Ethereum to the entities defined in your schema (e.g. mapping.ts in this tutorial)

The entries in subgraph.yaml that we will be working with are:

• description (optional): a human-readable description of what the subgraph is. This description is displayed by the Graph Explorer when the subgraph is deployed to the Hosted Service.
• repository (optional): the URL of the repository where the subgraph manifest can be found. This is also displayed by the Graph Explorer.
• dataSources.source: the address of the smart contract the subgraph sources, and the abi of the smart contract to use. The address is optional; omitting it allows to index matching events from all contracts.
• dataSources.source.startBlock (optional): the number of the block that the data source starts indexing from. In most cases we suggest using the block in which the contract was created.
• dataSources.mapping.entities : the entities that the data source writes to the store. The schema for each entity is defined in the the schema.graphql file.
• dataSources.mapping.abis: one or more named ABI files for the source contract as well as any other smart contracts that you interact with from within the mappings.
• dataSources.mapping.eventHandlers: lists the smart contract events this subgraph reacts to and the handlers in the mapping — ./src/mapping.ts in the example — that transform these events into entities in the store.

Defining the entities

With The Graph, you define entity types in schema.graphql, and Graph Node will generate top level fields for querying single instances and collections of that entity type. Each type that should be an entity is required to be annotated with an @entity directive.

The entities / data we will be indexing are the Token and User. This way we can index the Tokens created by the users as well as the users themselves.

To do this, update schema.graphql with the following code:

type Token @entity {
  id: ID!
  tokenID: BigInt!
  contentURI: String
  tokenIPFSPath: String
  name: String!
  createdAtTimestamp: BigInt!
  creator: User!
  owner: User!
}

type User @entity {
  id: ID!
  tokens: [Token!]! @derivedFrom(field: "owner")
  created: [Token!]! @derivedFrom(field: "creator")
}

On Relationships via @derivedFrom (from the docs):

Reverse lookups can be defined on an entity through the @derivedFrom field. This creates a virtual field on the entity that may be queried but cannot be set manually through the mappings API. Rather, it is derived from the relationship defined on the other entity. For such relationships, it rarely makes sense to store both sides of the relationship, and both indexing and query performance will be better when only one side is stored and the other is derived.

For one-to-many relationships, the relationship should always be stored on the 'one' side, and the 'many' side should always be derived. Storing the relationship this way, rather than storing an array of entities on the 'many' side, will result in dramatically better performance for both indexing and querying the subgraph. In general, storing arrays of entities should be avoided as much as is practical.

Now that we have created the GraphQL schema for our app, we can generate the entities locally to start using in the mappings created by the CLI:

graph codegen

In order to make working smart contracts, events and entities easy and type-safe, the Graph CLI generates AssemblyScript types from a combination of the subgraph's GraphQL schema and the contract ABIs included in the data sources.

Updating the subgraph with the entities and mappings

Now we can configure the subgraph.yaml to use the entities that we have just created and configure their mappings.

To do so, first update the dataSources.mapping.entities field with the User and Token entities:

entities:
  - Token
  - User

Next, update the dataSources.mapping.eventHandlers to include only the following three event handlers:

- event: TokenIPFSPathUpdated(indexed uint256,indexed string,string)
  handler: handleTokenIPFSPathUpdated
- event: Transfer(indexed address,indexed address,indexed uint256)
  handler: handleTransfer

Finally, update the configuration to add the startBlock and change the contract address to the main contract address:

source:
  address: "0x3B3ee1931Dc30C1957379FAc9aba94D1C48a5405"
  abi: Token
  startBlock: 11565020

Assemblyscript mappings

Next, open src/mappings.ts to write the mappings that we defined in our subgraph subgraph eventHandlers.

Update the file with the following code:

import {
  TokenIPFSPathUpdated as TokenIPFSPathUpdatedEvent,
  Transfer as TransferEvent,
  Token as TokenContract,
} from "../generated/Token/Token"

import {
  Token, User
} from '../generated/schema'

export function handleTransfer(event: TransferEvent): void {
  let token = Token.load(event.params.tokenId.toString());
  if (!token) {
    token = new Token(event.params.tokenId.toString());
    token.creator = event.params.to.toHexString();
    token.tokenID = event.params.tokenId;
  
    let tokenContract = TokenContract.bind(event.address);
    token.contentURI = tokenContract.tokenURI(event.params.tokenId);
    token.tokenIPFSPath = tokenContract.getTokenIPFSPath(event.params.tokenId);
    token.name = tokenContract.name();
    token.createdAtTimestamp = event.block.timestamp;
  }
  token.owner = event.params.to.toHexString();
  token.save();
    
  let user = User.load(event.params.to.toHexString());
  if (!user) {
    user = new User(event.params.to.toHexString());
    user.save();
  }
}

export function handleTokenURIUpdated(event: TokenIPFSPathUpdatedEvent): void {
  let token = Token.load(event.params.tokenId.toString());
  if (!token) return
  token.tokenIPFSPath = event.params.tokenIPFSPath;
  token.save();
}

These mappings will handle events for when a new token is created, transferred, or updated. When these events fire, the mappings will save the data into the subgraph.

Running a build

Next, let's run a build to make sure that everything is configured properly. To do so, run the build command:

graph build

If the build is successful, you should see a new build folder generated in your root directory.

Deploying the subgraph

To deploy, we can run the deploy command using the Graph CLI. To deploy, you will first need to copy the Access token for your account, available in the Graph Explorer:

Next, run the following command:

$ graph auth
✔ Product for which to initialize · hosted-service
✔ Deploy key · ********************************

yarn deploy

Once the subgraph is deployed, you should see it show up in your dashboard:

When you click on the subgraph, it should open the Graph explorer:

Querying for data

Now that we are in the dashboard, we should be able to start querying for data. Run the following query to get a list of tokens and their metadata:

{
  tokens {
    id
    tokenID
    contentURI
    tokenIPFSPath
  }
}

We can also configure the order direction:

{
  tokens(
    orderBy:id,
    orderDirection: desc
  ) {
    id
    tokenID
    contentURI
    tokenIPFSPath
  }
}

Or choose to skip forward a certain number of results to implement some basic pagination:

{
  tokens(
    skip: 100,
    orderBy:id,
    orderDirection: desc
  ) {
    id
    tokenID
    contentURI
    tokenIPFSPath
  }
}

Or query for users and their associated content:

{
  users {
    id
    tokens {
      id
      contentURI
    }
  }
}

We can also query by timestamp to view the most recently created NFTS:

{
  tokens(
    orderBy: createdAtTimestamp,
    orderDirection: desc
  ) {
    id
    tokenID
    contentURI
  }
}

The codebase for this project is located here

Next steps

If you are interested in learning more about Web3, building Dapps, or building subgraphs, check out the following resources:

The Graph on Twitter - @graphprotocol

The Complete Guide to Full Stack Ethereum Development

The Graph Discord

Solidity Docs

Ethereum Developer Documentation

Austin Griffith on Twitter @austingriffith & Scaffold Eth

Crypto Zombies