链上数据索引：The Graph、Subgraph 与数据查询架构

# subgraph.yaml
specVersion: 1.0.0
schema:
  file: ./schema.graphql
dataSources:
  - kind: ethereum/contract
    name: Token
    network: mainnet
    source:
      address: "0x6B175474E89094C44Da98b954EedeAC495271d0F"
      abi: ERC20
      startBlock: 5000000
    mapping:
      kind: ethereum/events
      apiVersion: 0.0.7
      language: wasm/assemblyscript
      entities:
        - Transfer
      abis:
        - name: ERC20
          file: ./abis/ERC20.json
      eventHandlers:
        - event: Transfer(address indexed from, address indexed to, uint256 value)
          handler: handleTransfer
      file: ./src/mapping.ts

# schema.graphql
type Transfer @entity {
  id: ID!
  from: Bytes!
  to: Bytes!
  value: BigInt!
  block: Int!
  timestamp: BigInt!
  transactionHash: Bytes!
}

type Holder @entity {
  id: ID!           # 地址
  balance: BigInt!  # 累计余额
  transfersIn: Int!
  transfersOut: Int!
}

// src/mapping.ts
import { Transfer as TransferEvent } from "../generated/Token/ERC20";
import { Transfer, Holder } from "../generated/schema";

export function handleTransfer(event: TransferEvent): void {
  // 1. 记录原始事件
  let transfer = new Transfer(
    event.transaction.hash.toHexString() + "-" + event.log.index.toString()
  );
  transfer.from = event.params.from;
  transfer.to = event.params.to;
  transfer.value = event.params.value;
  transfer.block = event.block.number.toI32();
  transfer.timestamp = event.block.timestamp;
  transfer.transactionHash = event.transaction.hash;
  transfer.save();

  // 2. 更新持有者聚合余额
  let holder = Holder.load(event.params.to.toHexString());
  if (holder == null) {
    holder = new Holder(event.params.to.toHexString());
    holder.balance = BigInt.fromI32(0);
    holder.transfersIn = 0;
    holder.transfersOut = 0;
  }
  holder.balance = holder.balance.plus(event.params.value);
  holder.transfersIn = holder.transfersIn + 1;
  holder.save();
}

// 用 ethers 解码日志
const iface = new ethers.Interface(abi);
const parsed = iface.parseLog(log);
// parsed.args.from / to / value 已结构化

# 1. 初始化子图
graph init --studio my-token-subgraph

# 2. 生成类型（从 schema + ABI）
graph codegen

# 3. 本地开发（可选：用 fork 节点测试）
graph deploy --node http://localhost:8020

# 4. 构建 & 部署到 Studio
graph build
graph deploy --studio my-token-subgraph

# 查询某地址的前 10 笔转账
query {
  transfers(
    first: 10,
    orderBy: block,
    orderDirection: desc,
    where: { from: "0x..." }
  ) {
    to
    value
    block
    timestamp
    transactionHash
  }
}

-- Dune Analytics 示例：查询 Uniswap V3 最大持币者
SELECT
  address,
  sum(value) AS total_value
FROM erc20_transfers
WHERE contract_address = lower('0x...')
GROUP BY address
ORDER BY total_value DESC
LIMIT 100;

# 伪代码：幂等索引循环
CHECKPOINT = "last_processed_block"
while True:
    head = get_head_block()
    while CHECKPOINT < head:
        logs = fetch_logs(CHECKPOINT, min(CHECKPOINT+1000, head))
        tx_apply(logs)          # 幂等：重复处理不重复写入
        CHECKPOINT = last_block(logs)  # 原子提交
    sleep(poll_interval)

# 伪代码：链上风控特征
def risk_features(address):
    return {
        "tx_count": count_transactions(address),
        "age_days": (now - first_tx_time(address)).days,
        "unique_counterparties": len(unique_addresses(address)),
        "max_single_value": max(tx_values(address)),
        "interacted_with_sanctioned": bool(links_to_sanctioned(address)),
    }