Ethereum Quick Start - Gravatar (Simple)

SubQuery TeamAbout 3 min

Ethereum Quick Start - Gravatar (Simple)

The goal of this quick start guide is to index all Ethereum Gravatars created or updated on the Ethereum mainnet.

In the earlier Quickstart section , you should have taken note of three crucial files. To initiate the setup of a project from scratch, you can proceed to follow the steps outlined in the initialisation description.

As a prerequisite, you will need to generate types from the ABI files of each smart contract. Additionally, you can kickstart your project by using the EVM Scaffolding approach (detailed here). You'll find all the relevant events to be scaffolded in the documentation for each type of smart contract.

Note

The final code of this project can be found here.

Check out how to get the Ethereum starter project running

Your Project Manifest File

The Project Manifest file is an entry point to your project. It defines most of the details on how SubQuery will index and transform the chain data.

For EVM chains, there are three types of mapping handlers (and you can have more than one in each project):

BlockHanders: On each and every block, run a mapping function
TransactionHandlers: On each and every transaction that matches optional filter criteria, run a mapping function
LogHanders: On each and every log that matches optional filter criteria, run a mapping function

Since we are indexing all Gravatars from the Gravatar contract, the first step is to import the contract abi definition. Copy the entire JSON and save it as a file called ./Gravity.json in the /abis directory.

This section in the Project Manifest now imports all the correct definitions and lists the triggers that we look for on the blockchain when indexing.

Since you are going to index all Gravatars, you need to update the datasources section as follows:

{
  dataSources: [
    {
      kind: EthereumDatasourceKind.Runtime,
      startBlock: 6175243,

      options: {
        // Must be a key of assets
        abi: "gravity",
        address: "0x2E645469f354BB4F5c8a05B3b30A929361cf77eC",
      },
      assets: new Map([["gravity", { file: "./abis/Gravity.json" }]]),
      mapping: {
        file: "./dist/index.js",
        handlers: [
          {
            kind: EthereumHandlerKind.Event,
            handler: "handleNewGravatar",
            filter: {
              topics: ["NewGravatar(uint256,address,string,string)"],
            },
          },
          {
            kind: EthereumHandlerKind.Event,
            handler: "handleUpdatedGravatar",
            filter: {
              topics: ["UpdatedGravatar(uint256,address,string,string)"],
            },
          },
        ],
      },
    },
  ],
}

The above code indicates that you will be running a handleLog mapping function whenever there is an NewGravatar or UpdatedGravatar log on any transaction from the Gravatar contract.

Note

Check out our Manifest File documentation to get more information about the Project Manifest (project.ts) file.

Update Your GraphQL Schema File

The schema.graphql file determines the shape of your data from SubQuery due to the mechanism of the GraphQL query language. Hence, updating the GraphQL Schema file is the perfect place to start. It allows you to define your end goal right at the start.

Remove all existing entities and update the schema.graphql file as follows. Here you can see we are indexing the id, owner, display name, image URL and the block the gravatar was created in.

type Gravatar @entity {
  id: ID!
  owner: Bytes!
  displayName: String!
  imageUrl: String!
  createdBlock: BigInt!
}

Note

Importantly, these relationships can not only establish one-to-many connections but also extend to include many-to-many associations. To delve deeper into entity relationships, you can refer to this section. If you prefer a more example-based approach, our dedicated Hero Course Module can provide further insights.

SubQuery simplifies and ensures type-safety when working with GraphQL entities, smart contracts, events, transactions, and logs. The SubQuery CLI will generate types based on your project's GraphQL schema and any contract ABIs included in the data sources.

yarn

yarn codegen

npm

npm run-script codegen

This action will generate a new directory (or update the existing one) named src/types. Inside this directory, you will find automatically generated entity classes corresponding to each type defined in your schema.graphql. These classes facilitate type-safe operations for loading, reading, and writing entity fields. You can learn more about this process in the GraphQL Schema section.

It will also generate a class for every contract event, offering convenient access to event parameters, as well as information about the block and transaction from which the event originated. You can find detailed information on how this is achieved in the EVM Codegen from ABIs section. All of these types are stored in the src/types/abi-interfaces and src/types/contracts directories.

You can conveniently import all these types:

import { Gravatar } from "../types";
import {
  NewGravatarLog,
  UpdatedGravatarLog,
} from "../types/abi-interfaces/Gravity";

Check out the GraphQL Schema documentation to get in-depth information on schema.graphql file.

Now that you have made essential changes to the GraphQL Schema file, let’s proceed ahead with the Mapping Function’s configuration.

Add a Mapping Function

Mapping functions define how blockchain data is transformed into the optimised GraphQL entities that we previously defined in the schema.graphql file.

Now that you have made essential changes to the GraphQL Schema file, let’s proceed ahead with the Mapping Function’s configuration.

3. Add a Mapping Function

Mapping functions define how chain data is transformed into the optimised GraphQL entities that we previously defined in the schema.graphql file.

Follow these steps to add a mapping function:

Navigate to the default mapping function in the src/mappings directory. You will be able to see three exported functions: handleBlock, handleLog, and handleTransaction. Replace these functions with the following code (note the additional imports):

import {
  NewGravatarLog,
  UpdatedGravatarLog,
} from "../types/abi-interfaces/Gravity";
import { Gravatar } from "../types";
import assert from "assert";

export async function handleNewGravatar(log: NewGravatarLog): Promise<void> {
  logger.info("New Gravar at block " + log.blockNumber.toString());

  assert(log.args, "Require args on the logs");

  const gravatar = Gravatar.create({
    id: log.args.id.toHexString()!,
    owner: log.args.owner,
    displayName: log.args.displayName,
    imageUrl: log.args.imageUrl,
    createdBlock: BigInt(log.blockNumber),
  });

  await gravatar.save();
}

export async function handleUpdatedGravatar(
  log: UpdatedGravatarLog,
): Promise<void> {
  logger.info("Updated Gravar at block " + log.blockNumber.toString());

  assert(log.args, "Require args on the logs");

  const id: string = log.args.id.toHexString()!;

  // We first check if the Gravatar already exists, if not we create it
  let gravatar = await Gravatar.get(id);
  if (gravatar == null || gravatar == undefined) {
    gravatar = Gravatar.create({
      id,
      createdBlock: BigInt(log.blockNumber),
      owner: "",
      displayName: "",
      imageUrl: "",
    });
  }
  // Update with new data
  gravatar.owner = log.args.owner;
  gravatar.displayName = log.args.displayName;
  gravatar.imageUrl = log.args.imageUrl;
  await gravatar.save();
}

Let’s understand how the above code works.

For handleNewGravatar, the function here receives an NewGravatarEvent which includes transaction log data in the payload. We extract this data and then create a new Gravatar entity that we defined in our schema.graphql and then save this to the store using the .save() function (Note that SubQuery will automatically save this to the database).

For handleUpdatedGravatar, the function here receives an UpdatedGravatarEvent which includes transaction log data in the payload. We extract this data and then first check that the Gravatar already exists, if not we instantiate a new one and then update that Gravatar with the correct updated details. This is then saved to the store using the .save() function (Note that SubQuery will automatically save this to the database).

Note

For more information on mapping functions, please refer to our Mappings documentation.

Build Your Project

Next, build your work to run your new SubQuery project. Run the build command from the project's root directory as given here:

yarn

yarn build

npm

npm run-script build

Important

Whenever you make changes to your mapping functions, you must rebuild your project.

Now, you are ready to run your first SubQuery project. Let’s check out the process of running your project in detail.

Whenever you create a new SubQuery Project, first, you must run it locally on your computer and test it and using Docker is the easiest and quickiest way to do this.

Run Your Project Locally with Docker

The docker-compose.yml file defines all the configurations that control how a SubQuery node runs. For a new project, which you have just initialised, you won't need to change anything.

However, visit the Running SubQuery Locally to get more information on the file and the settings.

Run the following command under the project directory:

yarn

yarn start:docker

npm

npm run-script start:docker

Note

It may take a few minutes to download the required images and start the various nodes and Postgres databases.

Query your Project

Next, let's query our project. Follow these three simple steps to query your SubQuery project:

Open your browser and head to http://localhost:3000.
You will see a GraphQL playground in the browser and the schemas which are ready to query.
Find the Docs tab on the right side of the playground which should open a documentation drawer. This documentation is automatically generated and it helps you find what entities and methods you can query.

Try the following queries to understand how it works for your new SubQuery starter project. Don’t forget to learn more about the GraphQL Query language.

query {
  gravatars(first: 2, orderBy: CREATED_BLOCK_DESC) {
    nodes {
      id
      owner
      displayName
      imageUrl
      createdBlock
    }
  }
}

You will see the result similar to below:

{
  "data": {
    "gravatars": {
      "nodes": [
        {
          "id": "0x47",
          "owner": "\\xbc8dafeaca658ae0857c80d8aa6de4d487577c63",
          "displayName": "Victor",
          "imageUrl": "https://ucarecdn.com/295e4ba5-ad1c-48bf-9957-093424709881/-/crop/152x152/1,0/-/preview/",
          "createdBlock": "6469958"
        },
        {
          "id": "0x46",
          "owner": "\\x0773cbc2c55cd6354a61b7bcbca52d9dccd56534",
          "displayName": "dgogel",
          "imageUrl": "https://ucarecdn.com/c44402a0-30f8-4c0c-bf1f-b13918903211/-/crop/512x512/0,0/-/preview/",
          "createdBlock": "6460716"
        }
      ]
    }
  }
}

Note

The final code of this project can be found here.

What's next?

Congratulations! You have now a locally running SubQuery project that accepts GraphQL API requests for transferring data.

Tip

Find out how to build a performant SubQuery project and avoid common mistakes in Project Optimisation.

Click here to learn what should be your next step in your SubQuery journey.