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Version: FireSquid

Custom GraphQL resolvers

One can extend the GraphQL API generated by OpenReader with custom queries. To do that, one can define GraphQL query resolvers in the designated module src/server-extension/resolvers. Note that all resolver classes (including any additional types) must be exported by src/server-extension/resolvers/index.ts.

A custom resolver should import TypeGraphQL types and use annotations provided by the library to define query arguments and return types.

Custom resolvers are normally used in combination with TypeORM EntityManager for accessing the API server target database. It is automatically injected when defined as a single constructor argument of the resolver.

Examples

Simple entity counter

import { Query, Resolver } from 'type-graphql'
import type { EntityManager } from 'typeorm'
import { Burn } from '../model'

@Resolver()
export class CountResolver {
constructor(private tx: () => Promise<EntityManager>) {}

@Query(() => Number)
async totalBurns(): Promise<number> {
const manager = await this.tx()
return await manager.getRepository(Burn).count()
}
}

This example is designed to work with the evm template: just grab a test squid as described here, write the example code to src/server-extension/resolver.ts and observe the totalBurns selection appear in the GraphiQL playground.

Custom SQL query

import { Arg, Field, ObjectType, Query, Resolver } from 'type-graphql'
import type { EntityManager } from 'typeorm'
import { MyEntity } from '../model'

// Define custom GraphQL ObjectType of the query result
@ObjectType()
export class MyQueryResult {
@Field(() => Number, { nullable: false })
total!: number

@Field(() => Number, { nullable: false })
max!: number

constructor(props: Partial<MyQueryResult>) {
Object.assign(this, props);
}
}

@Resolver()
export class MyResolver {
// Set by depenency injection
constructor(private tx: () => Promise<EntityManager>) {}

@Query(() => [MyQueryResult])
async myQuery(): Promise<MyQueryResult[]> {
const manager = await this.tx()
// execute custom SQL query
const result: = await manager.getRepository(MyEntity).query(
`SELECT
COUNT(x) as total,
MAX(y) as max
FROM my_entity
GROUP BY month`)
return result
}
}

More examples

Some great examples of @subsquid/graphql-server-based custom resolvers can be spotted in the wild in the Rubick repo by KodaDot.

For more examples of resolvers, see TypeGraphQL examples repo.