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Configuring the schema
Configuring the schemaUsing "field to input"

Using "field to input"

Obtain the value of a field, manipulate it, and input it into another field, all within the same query.

How to use

The field to obtain the value from is referenced using the "Variable" syntax $, and __ before the field alias or name. (For instance, the value from field excerpt is referenced as $__excerpt.) The response from the second field can itself be used as input to another field:

{
  posts {
    excerpt
 
    # Referencing previous field with name "excerpt"
    isEmptyExcerpt: _isEmpty(value: $__excerpt)
 
    # Referencing previous field with alias "isEmptyExcerpt"
    isNotEmptyExcerpt: _not(value: $__isEmptyExcerpt)
  }
}

The response will be:

{
  "data": {
    "posts": [
      {
        "excerpt": "Some post excerpt",
        "isEmptyExcerpt": false,
        "isNotEmptyExcerpt": true
      },
      {
        "excerpt": "",
        "isEmptyExcerpt": true,
        "isNotEmptyExcerpt": false
      }
    ]
  }
}

The field can only be referenced by any of its previous sibling fields in the same node. The following queries will NOT work:

# This will fail because the reference to the field must appear after the field, not before
{
  posts {
    isEmptyExcerpt: _isEmpty(value: $__excerpt)
    excerpt
  }
}
 
# This will fail because the reference must be done within the same node
{
  posts {
    excerpt
  }
  isEmptyExcerpt: _isEmpty(value: $__excerpt)
}

The field also cannot be referenced from a directive argument (for that, use the @passOnwards directive):

# This will fail because the reference can be only used as input to a field, not to a directive
{
  posts {
    hasComments
    title @include(if: $__hasComments)
  }
}

Examples

If the post's excerpt is empty, use the title instead:

{
  posts {
    title
    originalExcerpt: excerpt
    isEmptyExcerpt: _isEmpty(value: $__originalExcerpt)
    excerpt: if(condition: $__isEmptyExcerpt, then: $__title, else: $__originalExcerpt)
  }
}

Retrieve data from an external REST endpoint, and manipulate its data to suit your requirements.

{
  externalData: _getJSON(url: "https://example.com/rest/some-external-endpoint")
  userName: _extract(object: $__externalData, path: "data.user.name")
  userLastName: _extract(object: $__externalData, path: "data.user.surname")
}

This will produce:

{
  "data": {
    "externalData": {
      "data": {
        "user": {
          "id": 1,
          "name": "Leo",
          "surname": "Loso"
        }
      }
    },
    "userName": "Leo",
    "userLastName": "Loso"
  }
}

Using the @remove directive on externalData, we can also avoid printing the external endpoint source data in the response:

{
  externalData: _getJSON(url: "https://example.com/rest/some-external-endpoint") @remove
  userName: _extract(object: $__externalData, path: "data.user.name")
  userLastName: _extract(object: $__externalData, path: "data.user.surname")
}

This will now produce:

{
  "data": {
    "userName": "Leo",
    "userLastName": "Loso"
  }
}

Retrieve the posts for every user that mention the user's email:

{
  users {
    email
    posts(filter: { search: $__email }) {
      id
      title
    }
  }
}

Send a newsletter defining the to and from emails through the optionValue field:

mutation {
  fromEmail: optionValue(name: "admin_email")
  toEmail: optionValue(name: "subscribers_email_list_recipient_address")
  _sendEmail(
    from: {
      email: $__fromEmail
    }
    to: $__toEmail
    subject: "Weekly summary"
    messageAs: {
      html: "..."
    }
  )
}