Migrate Subgraph

If you have an existing subgraph project that you want to migrate to the Blockflow system, follow this guide to ensure a smooth transition.

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Configuring the studio.yaml file

Start by comparing your existing subgraph.yaml file with the studio.yaml file used in the Blockflow system. Both files serve as the entry point for configuring the subgraph, but the structure and naming conventions may differ.

• subgraph.yaml

specVersion: 0.0.2
description: ERC20 Subgraph
schema:
  file: ./schema.graphql
dataSources:
  - kind: ethereum/contract
    name: ERC20
    network: mainnet
    source:
      abi: ERC20
      startBlock: 0
    mapping:
      kind: ethereum/events
      apiVersion: 0.0.4
      language: wasm/assemblyscript
      entities:
        - Account
        - Token
        - TokenApproval
        - TokenBalance
      abis:
        - name: ERC20
          file: ./abis/ERC20.json
      eventHandlers:
        - event: Transfer(indexed address,indexed address,uint256)
          handler: handleTransfer
      file: ./src/mapping.ts

• studio.yaml

name: cli-demo
description: a project to showcase cli working
startBlock: latest
userId: XXXXXXXX-XXXX-XXXX-XXXXXXXX-XXXXXXXX
projectId: XXXXXXXX-XXXX-XXXX-XXXXXXXX-XXXXXXXX
network: Ethereum
user: Jane-doe
schema:
  file: ./studio.schema.ts
execution: parallel
Resources:
  - Name: usdt
    Abi: src/abis/usdt.json
    Type: contract/event
    Address: "0xdAC17F958D2ee523a2206206994597C13D831ec7"
    Triggers:
      - Event: Transfer(address indexed,address indexed,uint256)
        Handler: src/handlers/usdt/Transfer.TransferHandler

---

Comparing the Schema

Next, compare your existing schema.graphql file with the studio.schema.ts file used in the Blockflow system. While the schema.graphql file uses the GraphQL Schema Definition Language (SDL), the studio.schema.ts file utilizes TypeScript interfaces to define the data model and entities.

Ensure that all entities and their fields are correctly mapped between the two schema files. You may need to make adjustments to the studio.schema.ts file to ensure compatibility with the Blockflow system.

• schema.graphql

type Transfer @entity {
  id: ID!
  to: String! 
  from: String! 
  amount: String!
}

• studio.schema.ts

export interface Transfer {
  id: String;
  from_address: string;
  to_address: string;
  amount: Number;
}

During the migration process, it's important to note that the conversion between types and interfaces should be handled correctly:

1. Types to Interfaces: Any object types defined in the schema.graphql file should be converted to TypeScript interfaces in the studio.schema.ts file.

2. Interfaces to Types: Conversely, any interfaces defined in the schema.graphql file should be converted to TypeScript types in the studio.schema.ts file.

• schema.graphql

type Transfer {
  id: ID!
  from: Bytes!
  to: Bytes!
  value: BigInt!
}

interface Account {
  id: ID!
  balance: BigInt!
}

• studio.schema.ts

export interface Transfer {
  id: String;
  from: string;
  to: string;
  value: Number;
}

type Account = {
  id: String;
  balance: Number;
}

---

Transforming Mapping Handlers

In the Blockflow system, each handler function for a specific trigger (event or function) must be written in a separate file. This file structure aligns with the configuration defined in the studio.yaml file, where each trigger is listed with its corresponding handler file path.

Syntax Changes

When migrating from an existing subgraph to the Blockflow system, there are a few syntax changes you'll need to make in your handler functions:

Retrieving and Creating Entities:

• In the subgraph, you use the .load() function to retrieve entities.

• In blockflow, you should use a combination of findOne and create functions.

• First, use findOne to check if an entity with the given criteria exists. If it does, you can update and save the existing entity.

• If findOne returns null, meaning the entity does not exist, you can use the create function to create a new entity instance.

subgraph syntax

let transfer = new Transfer(entityId);  //to create new entity

let transfer = Transfer.load(entityId); //to load existing entity

blockflow syntax

let entity: ITransfer = await transferDB.create({id: entityId}); //to create
 
let entity: ITransfer = await transferDB.findOne({id: entityId}); //to load

Saving Entities:

• In the Blockflow system, there is a minor difference in the syntax for saving entities.

• Instead of using entity.save() directly, you should use the save function returned by the bind function.

• The save function takes the entity instance as an argument.

subgraph syntax

transfer.save();

blockflow syntax

await transferDB.save(entity);