The Graph QL Schema

Panoramica

The schema for your Subgraph is in the file schema.graphql. GraphQL schemas are defined using the GraphQL interface definition language.

Defining Entities

Before defining entities, it is important to take a step back and think about how your data is structured and linked.

• All queries will be made against the data model defined in the Subgraph schema. As a result, the design of the Subgraph schema should be informed by the queries that your application will need to perform.
• It may be useful to imagine entities as “objects containing data”, rather than as events or functions.
• You define entity types in schema.graphql, and Graph Node will generate top-level fields for querying single instances and collections of that entity type.
• Each type that should be an entity is required to be annotated with an @entity directive.
• By default, entities are mutable, meaning that mappings can load existing entities, modify them and store a new version of that entity.
  • Mutability comes at a price, so for entity types that will never be modified, such as those containing data extracted verbatim from the chain, it is recommended to mark them as immutable with @entity(immutable: true).
  • If changes happen in the same block in which the entity was created, then mappings can make changes to immutable entities. Immutable entities are much faster to write and to query so they should be used whenever possible.

Buon esempio

The following Gravatar entity is structured around a Gravatar object and is a good example of how an entity could be defined.

1type Gravatar @entity(immutable: true) {2  id: Bytes!3  owner: Bytes4  displayName: String5  imageUrl: String6  accepted: Boolean7}

Cattivo esempio

The following example GravatarAccepted and GravatarDeclined entities are based around events. It is not recommended to map events or function calls to entities 1:1.

1type GravatarAccepted @entity {2  id: Bytes!3  owner: Bytes4  displayName: String5  imageUrl: String6}78type GravatarDeclined @entity {9  id: Bytes!10  owner: Bytes11  displayName: String12  imageUrl: String13}

Campi opzionali e obbligatori

Entity fields can be defined as required or optional. Required fields are indicated by the ! in the schema. If the field is a scalar field, you get an error when you try to store the entity. If the field references another entity then you get this error:

1Null value resolved for non-null field 'name'

Each entity must have an id field, which must be of type Bytes! or String!. It is generally recommended to use Bytes!, unless the id contains human-readable text, since entities with Bytes! id’s will be faster to write and query as those with a String! id. The id field serves as the primary key, and needs to be unique among all entities of the same type. For historical reasons, the type ID! is also accepted and is a synonym for String!.

For some entity types the id for Bytes! is constructed from the id’s of two other entities; that is possible using concat, e.g., let id = left.id.concat(right.id) to form the id from the id’s of left and right. Similarly, to construct an id from the id of an existing entity and a counter count, let id = left.id.concatI32(count) can be used. The concatenation is guaranteed to produce unique id’s as long as the length of left is the same for all such entities, for example, because left.id is an Address.

Tipi scalari integrati

Scalari supportati da GraphQL

The following scalars are supported in the GraphQL API:

Enum

È possibile creare enum anche all’interno di uno schema. Gli enum hanno la seguente sintassi:

1enum TokenStatus {2  OriginalOwner3  SecondOwner4  ThirdOwner5}

Once the enum is defined in the schema, you can use the string representation of the enum value to set an enum field on an entity. For example, you can set the tokenStatus to SecondOwner by first defining your entity and subsequently setting the field with entity.tokenStatus = "SecondOwner". The example below demonstrates what the Token entity would look like with an enum field:

More detail on writing enums can be found in the GraphQL documentation⁠.

Relazioni tra entità

Un’entità può avere una relazione con una o più altre entità dello schema. Queste relazioni possono essere attraversate nelle query. Le relazioni in The Graph sono unidirezionali. È possibile simulare relazioni bidirezionali definendo una relazione unidirezionale su entrambe le “estremità” della relazione.

Le relazioni sono definite sulle entità come qualsiasi altro campo, tranne per il fatto che il tipo specificato è quello di un’altra entità.

Rapporti uno-a-uno

Define a Transaction entity type with an optional one-to-one relationship with a TransactionReceipt entity type:

1type Transaction @entity(immutable: true) {2  id: Bytes!3  transactionReceipt: TransactionReceipt4}56type TransactionReceipt @entity(immutable: true) {7  id: Bytes!8  transaction: Transaction9}

Relazioni uno-a-molti

Define a TokenBalance entity type with a required one-to-many relationship with a Token entity type:

1type Token @entity(immutable: true) {2  id: Bytes!3}45type TokenBalance @entity {6  id: Bytes!7  amount: Int!8  token: Token!9}

Ricerche inverse

Reverse lookups can be defined on an entity through the @derivedFrom field. This creates a virtual field on the entity that may be queried but cannot be set manually through the mappings API. Rather, it is derived from the relationship defined on the other entity. For such relationships, it rarely makes sense to store both sides of the relationship, and both indexing and query performance will be better when only one side is stored and the other is derived.

For one-to-many relationships, the relationship should always be stored on the ‘one’ side, and the ‘many’ side should always be derived. Storing the relationship this way, rather than storing an array of entities on the ‘many’ side, will result in dramatically better performance for both indexing and querying the Subgraph. In general, storing arrays of entities should be avoided as much as is practical.

Esempio

We can make the balances for a token accessible from the token by deriving a tokenBalances field:

1type Token @entity(immutable: true) {2  id: Bytes!3  tokenBalances: [TokenBalance!]! @derivedFrom(field: "token")4}56type TokenBalance @entity {7  id: Bytes!8  amount: Int!9  token: Token!10}

Here is an example of how to write a mapping for a Subgraph with reverse lookups:

1let token = new Token(event.address) // Create Token2token.save() // tokenBalances is derived automatically34let tokenBalance = new TokenBalance(event.address)5tokenBalance.amount = BigInt.fromI32(0)6tokenBalance.token = token.id // Reference stored here7tokenBalance.save()

Relazioni molti-a-molti

Per le relazioni molti-a-molti, come ad esempio gli utenti che possono appartenere a un numero qualsiasi di organizzazioni, il modo più semplice, ma generalmente non il più performante, di modellare la relazione è come un array in ciascuna delle due entità coinvolte. Se la relazione è simmetrica, è necessario memorizzare solo un lato della relazione e l’altro lato può essere derivato.

Esempio

Define a reverse lookup from a User entity type to an Organization entity type. In the example below, this is achieved by looking up the members attribute from within the Organization entity. In queries, the organizations field on User will be resolved by finding all Organization entities that include the user’s ID.

1type Organization @entity {2  id: Bytes!3  name: String!4  members: [User!]!5}67type User @entity {8  id: Bytes!9  name: String!10  organizations: [Organization!]! @derivedFrom(field: "members")11}

A more performant way to store this relationship is through a mapping table that has one entry for each User / Organization pair with a schema like

1type Organization @entity {2  id: Bytes!3  name: String!4  members: [UserOrganization!]! @derivedFrom(field: "organization")5}67type User @entity {8  id: Bytes!9  name: String!10  organizations: [UserOrganization!] @derivedFrom(field: "user")11}1213type UserOrganization @entity {14  id: Bytes! # Set to `user.id.concat(organization.id)`15  user: User!16  organization: Organization!17}

Questo approccio richiede che le query scendano di un ulteriore livello per recuperare, ad esempio, le organizzazioni degli utenti:

1query usersWithOrganizations {2  users {3    organizations {4      # this is a UserOrganization entity5      organization {6        name7      }8    }9  }10}

This more elaborate way of storing many-to-many relationships will result in less data stored for the Subgraph, and therefore to a Subgraph that is often dramatically faster to index and to query.

Aggiungere commenti allo schema

As per GraphQL spec, comments can be added above schema entity attributes using the hash symbol #. This is illustrated in the example below:

1type MyFirstEntity @entity {2  # unique identifier and primary key of the entity3  id: Bytes!4  address: Bytes!5}

Definizione dei campi di ricerca fulltext

Le query di ricerca fulltext filtrano e classificano le entità in base a un input di ricerca testuale. Le query full-text sono in grado di restituire corrispondenze per parole simili, elaborando il testo della query in gambi prima di confrontarli con i dati di testo indicizzati.

La definizione di una query fulltext include il nome della query, il dizionario linguistico utilizzato per elaborare i campi di testo, l’algoritmo di classificazione utilizzato per ordinare i risultati e i campi inclusi nella ricerca. Ogni query fulltext può comprendere più campi, ma tutti i campi inclusi devono appartenere a un unico tipo di entità.

To add a fulltext query, include a _Schema_ type with a fulltext directive in the GraphQL schema.

1type _Schema_2  @fulltext(3    name: "bandSearch"4    language: en5    algorithm: rank6    include: [{ entity: "Band", fields: [{ name: "name" }, { name: "description" }, { name: "bio" }] }]7  )89type Band @entity {10  id: Bytes!11  name: String!12  description: String!13  bio: String14  wallet: Address15  labels: [Label!]!16  discography: [Album!]!17  members: [Musician!]!18}

The example bandSearch field can be used in queries to filter Band entities based on the text documents in the name, description, and bio fields. Jump to GraphQL API - Queries for a description of the fulltext search API and more example usage.

1query {2  bandSearch(text: "breaks & electro & detroit") {3    id4    name5    description6    wallet7  }8}

Lingue supportate

La scelta di una lingua diversa avrà un effetto definitivo, anche se talvolta sottile, sull’API di ricerca fulltext. I campi coperti da una query fulltext vengono esaminati nel contesto della lingua scelta, quindi i lessemi prodotti dall’analisi e dalle query di ricerca variano da lingua a lingua. Ad esempio, quando si utilizza il dizionario turco supportato, “token” viene ridotto a “toke”, mentre il dizionario inglese lo riduce a “token”.

Dizionari linguistici supportati:

Algoritmi di classificazione

Algoritmi supportati per ordinare i risultati: