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Lambda Webhooks Example

It is a common need to populate a “Created At” date whenever a new data is created. Using Lambda Webhooks, the population of this field can be offloaded from the clients to a Dgraph Lambda. Lambda Webhooks are special kind of lambdas that are automatically invoked whenever data belonging to a GraphQL type is added, modified, or deleted.

Steps to run this example are as follows.

The GraphQL Schema

type Author @lambdaOnMutate(add: true, update: true, delete: true) {
    id: ID!
    name: String! @search(by: [hash, trigram])
    createdAt: DateTime
}

In the schema provided, there is a type Author which has an id, and name as well as a createAt field. The createdAt field is to be populated with the date when a new Author is created.

Please note that a special directive, lambdaOnMutate is configured. This configureation allowd Dgraph to invoke a lambda whenever an Author is added, updated or deleted.

Configuring the lambda

async function addAuthorWebhook({event, dql, graphql, authHeader}) {
    // execute what you want on addition of an author 
    // maybe send a welcome mail to the author
    console.log("new author added")
    console.log(event.add.rootUIDs[0])
    const createdDate = new Date()
    const createdAt = createdDate.toISOString();
    console.log(createdAt)
    const results = await graphql(`mutation UpdateCreatedDate($id: ID!, $createdAt: DateTime!) {
  updateAuthor(input: {filter: {id: [$id] }, set: {createdAt: $createdAt}}) {
    author {
      id
      name
      createdAt
    }
  }
}
`, {"id": event.add.rootUIDs[0], "createdAt" : createdAt})
    
}

async function updateAuthorWebhook({event, dql, graphql, authHeader}) {
    // execute what you want on updation of an author
    // maybe send a mail to the author informing that few details have been updated 
    
}

async function deleteAuthorWebhook({event, dql, graphql, authHeader}) {
    // execute what you want on deletion of an author
    // maybe mail the author saying they have been removed from the platform 
    
}

self.addWebHookResolvers({
    "Author.add": addAuthorWebhook,
    "Author.update": updateAuthorWebhook,
    "Author.delete": deleteAuthorWebhook,
})

The addAuthorWebhook function configured such that it is invoked whenever a new Author is added. The addAuthorWebhook receives an event object which contains the context of the add, update or delete action. In this example, the event contains the uid of the newly created Author in the field event.add.rootUIDs[0].

Mutation to add an Author

mutation AddAuthor {
  addAuthor(input: {name: "John"}) {
    numUids
  }
}

This mutation will add an Author. Please note that only the name is provided by the client and the createdAt field is not provided by the client. Upon execution of this mutation, the addAuthorWebhook function configured previously will be invoked by Dgraph. This function retrieves the uid of the newly created Author and updates the createdAt attribute for this uid.

When you query the data subsequently, you will now see the following data. The createdAt field is now populated with a date.

{
  "id": "0xd",
  "name": "John",
  "createdAt": "2021-07-16T05:28:06.433Z"
}

Summary

In this example, we saw an example of the lambda webhook using the lambdaOnMutate directive. We used a lambda webhook to auto-populate the createdAt attribute for a newly created Author. The advantage of this approach is that the client need not pass attributes that can be determined on the server side. This keeps the client code lightweight and easy to manage.