Icon LinkGraphQL Schema

The GraphQL schema is a required component of the Fuel indexer. When data is indexed into the database, the actual values that are persisted to the database will be values created using the data structures defined in the schema.

In its most basic form, a Fuel indexer GraphQL schema should have a schema definition that contains a defined query root. The rest of the implementation is up to you. Here's an example of a well-formed schema:

type FirstThing @entity {
    id: ID!
    value: UInt8!
}
 
type SecondThing @entity {
    id: ID!
    optional_value: UInt8
    timestamp: Timestamp!
}

The types you see above (e.g., ID, UInt8, etc) are Fuel abstractions that were created to more seamlessly integrate with the Fuel VM and are not native to GraphQL. A deeper explanation on these types can be found in the Types section .

Important: It is up to developers to manage their own unique IDs for each type, meaning that a data structure's ID field needs to be manually generated prior to saving it to the database. This generation can be as simple or complex as you want in order to fit your particular situation; the only requirement is that the developer implement their own custom generation.

Icon LinkRequired and Optional Fields

Required fields are denoted with a ! following its type; for example, the value field of the FirstThing type is a UInt8 and is required to be present for the indexer to successfully persist the entity. If a certain piece of information is essential to your use case, then you should mark that field as required.

In contrast, optional fields are not required to be present for the indexer to persist the entity in storage. You can denote an optional field by just using the type name; for example, the optional_value field of the SecondThing type is optional, and should be a UInt8 if present. If it's possible that a value might not always exist in the data you wish to index, consider making that the corresponding field optional. In your indexer code, you will need to use the Option Rust type when assigning a value to an optional field; values that are present should be assigned after being wrapped in Some(..) while absent values should be assigned using None.

Important: The ID field is always required. An indexer will return an error if an optional value is used for the ID field.