[区块链]thegraph入门教程

编写智能合约时，通常状态的变化是通过触发一个事件来表达，The Graph则是捕捉区块链事件并提供一个查询事件的GraphQL接口，让我们可以方便的跟踪数据的变化。 实际上很多 DEFI 协议及都是The Graph来基于查询数据。
https://thegraph.academy/developers/local-development/
我们以此教程为基础做出一下额外的补充。
工具准备：nodejs、yarn、docker、truffle、graph-cli

1. 合约开发与部署

1. 合约的开发环境搭建
   npm install -g truffle ganache-cli

2. 合约编写
   该合约为手写的测试合约，主要定义了两个事件，PairCreated和AddLiquidity。我们用thegarph来监听以下的事件。

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Pair{

    string private _name;

    uint private _liquidity;

    constructor(string memory name){
        _name = name;
    }

    function addLiquidity(uint amount) public {
        _liquidity+=amount;
    }

    function getLiquidity() public view returns(uint){
        return _liquidity;
    }

    function getName() public view returns(string memory){
        return _name;
    }

}

contract Dex {

    address private _owner;

    uint private _index = 0;

    mapping(address => Pair) private _pairs;

    mapping(uint => address) private _indexs;

    modifier onlyOwner(){
        require(msg.sender == _owner,"must be owner");
        _;
    }

    event PairCreated(string name, address pairAddress);

    event AddLiquidity(address pairAddress, uint liquidity);


    function createPair(string memory name) public {
        Pair pair = new Pair(name);
        _pairs[address(pair)] = pair;
        _indexs[_index] = address(pair);
        _index++;

        emit PairCreated(name, address(pair));
    }

    function addLiquidity(address pairAddress,uint liquidity) public {
        _pairs[pairAddress].addLiquidity(liquidity);

        emit AddLiquidity(pairAddress,liquidity);
    }


    function getCount() public view returns(uint){
        return _index;
    }

    function pairAddress(uint index) public view returns(address){
        return _indexs[index];
    }

    
    function getPairName(address pairAddress) public view returns(string memory){
        return _pairs[pairAddress].getName();
    }


    function getLiquidity(address pairAddress) public view returns(uint liquidity){
        return _pairs[pairAddress].getLiquidity();
    }
}

3. 通过truffle部署到自建的ganache区块链上
   truffle migrate

4. 通过remix调用合约写入数据触发事件

2. 创建索引数据的Subgraph

TheGraph中定义如何为数据建立索引，称为Subgraph，它包含三个组件：

1. Manifest 清单(subgraph.yaml) - 定义配置项

specVersion: 0.0.1
description: study
repository: https://github.com/graphprotocol/example-subgraph
schema:
 file: ./schema.graphql
dataSources:
 - kind: ethereum/contract
   name: study
   network: mainnet
   source:
     address: '0xf80e65c3c1B49626bae2ECE7e67A3e1AdBD480C2'
     abi: Dex
   mapping:
     kind: ethereum/events
     apiVersion: 0.0.5
     language: wasm/assemblyscript
     entities:
       - Pairs
     abis:
       - name: Dex
         file: ./build/contracts/Dex.json
     eventHandlers:
       - event: PairCreated(string,address)
         handler: handleNewPairCreated
       - event: AddLiquidity(address,uint256)
         handler: handleAddLiquidity
     file: ./src/mapping.ts

2. Schema 模式(schema.graphql) - 定义数据

type Pair @entity {
  id: ID!
  displayName: String!
  liquidity: Int!
}

3. 生成代码
   graph codegen

4. Mapping 映射(mapping.ts) - 定义事件到数据的转换

import {AddLiquidity, PairCreated} from '../generated/study/Dex'
import {Pair} from '../generated/schema'

export function handleNewPairCreated(event: PairCreated): void {
    let pair = new Pair(event.params.pairAddress.toHexString())
    pair.displayName = event.params.name
    pair.liquidity = 0
    pair.save()
}

export function handleAddLiquidity(event: AddLiquidity): void {
    let id = event.params.pairAddress.toHexString()
    let pair = Pair.load(id)
    if (pair == null) {
        return
    }
    pair.liquidity += event.params.liquidity.toI32()
    pair.save()
}

3. 部署Subgraph到TheGraph，实现数据索引

1. 以搭建本地节点为例,运行graph-node

git clone https://github.com/graphprotocol/graph-node/

cd graph-node/docker

docker compose up

2. 安装项目依赖&&部署到graph节点上

yarn && yarn codegen

yarn create-local

yarn deploy-local

4. 在graphql查询数据

query{
  pairs(first:10){
    id,
    displayName,
    liquidity
  }
}

显示结果如下

5. 踩坑指南

1. Failed to deploy to Graph node http://127.0.0.1:8020/: Ethereum network not supported by registrar: mainnet.
   是因为我本地起到的ganache区块链网络，graph-node在容器内无法找到宿主机的IP，更改了docker/docker-compose.yml里的配置ethereum: ‘mainnet:http://docker.for.mac.host.internal:8545’