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Schema Coordinates

At a glance​

  • Identifier: SchemaCoordinates
  • Stage: RFC0: Strawman
  • Champion: -
  • PR: -
  • Related:
    • #733 (Tagged type)

Timeline​

RFC: Schema Coordinates

Proposed by: Mark Larah - Yelp

This RFC proposes formalizing "Schema Coordinates" - a human readable syntax to uniquely identify a type, field, field argument, enum value, directive or directive argument defined in a GraphQL Schema.

This should be listed as a non-normative note in the GraphQL specification to serve as an official reference for use by third party tooling.

📜 Problem Statement​

GraphQL tooling and libraries may wish to refer to various components of a GraphQL schema. Use cases include documentation, metrics and logging libraries.

(Example shown from GraphiQL's documentation search tab)

There already exists a convention used by some libraries and tools for writing out fields in a unique way for such purposes. However, there is no formal specification or name for this convention.

Use cases​

  1. A GraphQL server wants to log how often each field in the schema is requested. This may be implemented by incrementing a counter by the name of the schema coordinate for each field executed in a request.

    Existing implementations: Yelp (internal), Facebook (internal), Shopify (API health report)

  2. GraphiQL and other playgrounds / documentation sites want to show a list of search results when a user searches for a type or field name. We can display a list of schema coordinates that match the search term. A schema coordinate can also be used in the hyperlink to form a permalink for documentation for a particular field.

    Existing implementations: GraphiQL, Apollo Studio (see "Prior Art")

  3. A developer may want to perform analytics on all known persisted queries - e.g. what are the most commonly used fields across all documents. Schema coordinates may be used as the index/lookup keys when storing this information in the database.

    Existing implementations: Yelp (internal)

  4. A GitHub bot may want to warn developers in a Pull Request comment whenever the schema diff contains a breaking change. Schema coordinates can be used to provide a list of which fields were broken.

    Existing implementations: GraphQL Inspector (see "Prior Art")

  5. GraphQL IDEs (e.g. GraphiQL, GraphQL Playground, Apollo Studio) may wish to display the schema definition type of a node in a query when hovering over it.

    Details

    Example

    Schema coordinates can be used to form the left hand side of this popover.

Existing implementations: Apollo Studio (see "Prior Art")

✅ RFC Goals​

  • There be one, unambiguous way to write a "schema coordinate" that refers to a particular element in a GraphQL schema. (This is to avoid users having to "simplify" more complex coordinates to produce a canonical representation.)
  • Schema coordinate syntax should build off of existing de-facto standards already adopted for this purpose (i.e. Foo.bar)
  • Schema coordinate syntax is open for extension in the future. We should make design choices that give us flexibility and anticipate future syntax needs (based off of discussions around this RFC).

🚫 RFC Non-goals​

  • This does not cover "selectors" or "wildcard" syntax - e.g. User.*. (See alternatives considered.)
  • There are no proposed GraphQL language/syntax changes
  • There are no proposed GraphQL runtime changes
  • Schema coordinate non-goals

🧑‍💻 Proposed syntax​

Type​

Refers to a named type (e.g. something represented by __typename in a GraphQL introspection call).

Type.attribute​

Refers to a named attribute on the named type.

Not all types support this. For object types and interface types this is a field, for input objects this would be an input field, for enums this would be an enum value, for future GraphQL types this will relate to a related concept if they have one (e.g. for the proposed "tagged" type it would refer to the "member field").

Type.field(argName:)​

Refers to a named argument on the named field of the named type.

@directive​

References the given named directive

@directive(argName:)​

References the named argument of the named directive.

✨ Examples​

For example, consider the following schema:

directive @private(scope: String!) on FIELD

type Person {
  name: String
  email: String @private(scope: "loggedIn")
}

type Business {
  name: String
  owner: Person
}

type Query {
  searchBusinesses(name: String): [Business]
}

We can write the following schema coordinates:

  • Person uniquely identifies the the "Person" type
  • Business uniquely identifies the the "Business" type
  • Person.name uniquely identifies the "name" field on the "Person" type
  • Business.name uniquely identifies the "name" field on the "Business" type
  • Business.owner uniquely identifies the "owner" field on the "Business" type
  • Query.searchBusinesses uniquely identifies the "searchBusinesses" field on the "Query" type
  • Query.searchBusinesses(name:) uniquely identifies the "name" argument on the "searchBusinesses" field on the "Query" type
  • @private uniquely identifies the "private" directive
  • @private(scope:) uniquely identifies the "scope" argument on the "private" directive

🎨 Prior art​

  • The name "schema coordinates" is inspired from GraphQL Java (4.3k stars), where "field coordinates" are already used in a similar way as described in this RFC.

  • GraphiQL displays schema coordinates in its documentation search tab:

  • GraphQL Inspector (840 stars) shows schema coordinates in its output:

  • Apollo Studio shows schema coordinates when hovering over fields in a query:

🥣 Document -> Schema Coordinate serialization​

Use cases 3 and 5 above imply that a mapping from GraphQL query nodes to schema coordinates is performed.

For example, consider the following schema:

type Person {
  name: String
}

type Business {
  name: String
  owner: Person
}

type Query {
  searchBusiness(name: String): [Business]
}

And the following query:

query {
  searchBusinesses(name: "El Greco Deli") {
    name
    owner {
      name
    }
  }
}

From the query above, we may calculate the following list of schema coordinates:

  • Query.searchBusinesses
  • Business.name
  • Business.owner
  • Person.name

Query.searchBusinesses(name:) is also a valid member of the output set. The serialization algorithm may optionally choose to output all permutations of field arguments used, should this be specified.

A library has been written to demonstrate this mapping: https://github.com/sharkcore/extract-schema-coordinates.

🗳️ Alternatives considered​

Naming​

  • "Schema Selectors"

    "Selectors" is a term used in HTML and CSS to select parts of an HTML document.

    This would be a compelling, familiar choice - however, we've decided to not support wildcard expansion in this spec. See the section Syntax Non-goals.

  • "type/field pairs"

    This was the original working name. However, there already exists more established terminology for this concept, and we also wish to describe more than just types on fields.

  • "Field Coordinates"

    "Field Coordinates" is already understood and used by the popular GraphQL Java project.

    Feedback in the August GraphQL Working Group meeting hinted that since we're targeting also describing arguments, field coordinates might not be the right name. Hence "Schema Coordinates" is chosen instead, as a more generalized form of this.

  • "GraphQL Coordinates"

    Similar to Field Coordinates/Schema Coordinates - however, "GraphQL Coordinates" is potentially ambiguous as to if it describes schema members, query/document members or response object members.

  • "Field path" / "GraphQL path"

    path exists as an attribute on GraphQLResolveInfo.

    Given the following query:

    query {
      searchBusinesses(name: "El Greco Deli") {
        name
        owner {
          name
        }
      }
    }

    Person.name in the response may be written as the following "field path":

    ["query", "searchBusinesses", 1, "owner", "name"]

    Note that here, the "path" is a serialized response tree traversal, instead of describing the location of the field in the schema.

    Since "path" is already used in GraphQL nomenclature to describe the location of a field in a response, we'll avoid overloading this term.

Separator​

This RFC proposes using "." as the separator character between a type and field. The following have also been proposed:

  • Foo::bar
  • Foo#bar
  • Foo->bar
  • Foo~bar
  • Foo:bar

"." is already used in the existing implementations of field coordinates, hence the suggested usage in this RFC. However, we may wish to consider one of the alternatives above, should this conflict with existing or planned language features.

Field Arguments​

We have discussed multiple options for selecting arguments on fields. (PR, and December WG Meeting). For example, consider the following schema:

type Query {
  rollDice(numDice: Int, numSides: Int): Int
}

We may want to refer to the numDice argument in a schema selector. Two options for this syntax are:

  1. Query.rollDice.numDice
  2. Query.rollDice(numDice:)

Pros for Query.rollDice.numDice​

  • Less bytes/characters to type
  • May allow for extension to include nested "field paths" (e.g. Foo.bar.Baz.qux...)
  • Prior usage of this syntax to represent state internally

Pros for Query.rollDice(numDice:)​

  • Indicating arguments with colons disambiguates against other types of schema nodes. For those unfamiliar with schema selectors, it may be unclear if the third dot separated item refers to a directive or a child object etc.
  • Using trailing colons for arguments is borrowed from other languages (e.g. [Swift][swift]). This may indicate to users who are unfamiliar with schema coordinates, but recognize this from other languages, that numDice: refers to an argument. The function parentheses and colons more strongly communicate "this is an argument!" than a second dot separator.

Decision​

We are choosing Query.rollDice(numDice:) to optimize for readability and extensibility.

Given our expected use cases, we assume Schema Coordinates will be read more often than they are written (e.g. error messages in a stack trace from a schema linting tool). Readers may be unfamiliar with its syntax. We want to "hint" as much as possible the meaning of the coordinates in its syntax. We think (numDice:) more clearly communicates that "numDice" is an argument, over .numDice.

In addition, we want to be mindful of extensions to this syntax in the future. Using dots only as a separator may overload the meaning of elements in schema coordinates in the future. (If we capture new schema node types, or nested paths.)

We should make sure that the spec enables future innovation including using it for things other than schema coordinates. To my mind the (foo:) syntax is more flexible in this regard. For example, I can imagine referring to:

  1. Foo.bar(baz.qux:): the qux field of the input object referred to from the baz argument of the bar field on the Foo type.
  2. Foo.bar(baz:).qux: the qux field on the return type of the bar field (with baz: argument) of the Foo type.
  3. Foo.bar.baz.qux: the qux field of the return type of the baz field on the return type of the bar field on type Foo.

If we were to only use periods then all of these would come out the same as Foo.bar.baz.qux, and this ambiguity precludes this kind of reusal of the schema-coordinates syntax for this use case (which is outside the scope of the schema coordinates spec, for sure, but is still a potential use-case for the syntax).

~ benjie

🙅 Syntax Non-goals​

This syntax consciously does not cover the following use cases:

  • Wildcard selectors

    Those familiar with document.querySelector may be expecting the ability to pass "wildcards" or "star syntax" to be able to select multiple schema elements. This implies multiple ways of selecting a schema node.

    For example, User.address and User.a* might both resolve to User.address. But User.a* could also ambiguously refer to User.age.

    It's unclear how wildcard expansion would work with respect to field arguments*, potentially violating the requirement of this schema to uniquely identify schema components.

    * (e.g. does Query.getUser also select all arguments on the getUser field? Who knows! A discussion for another time.)

    A more general purpose schema selector language could be built on top of this spec - however, we'll consider this out of scope for now.

  • Nested field paths

    This spec does not support selecting schema members with a path from a root type (e.g. Query).

    For example, given this schema

    type User {
      name: String
      bestFriend: User
    }

    type Query {
      userById(id: String): User
    }

    The following are invalid schema coordinates:

    • Query.userById.name
    • User.bestFriend.bestFriend.bestFriend.name

    This violates a non-goal that there be one, unambiguous way to write a schema coordinate to refer to a schema member. Both examples can be "simplified" to User.name, which is a valid schema coordinate.

    Should a use case for this arise in the future, a follow up RFC may investigate how schema coordinates could work with "field paths" (e.g. ["query", "searchBusinesses", 1, "owner", "name"]) to cover this.

  • Directive applications

    This spec does not support selecting applications of directive.

    For example:

    directive @private(scope: String!) on FIELD

    type User {
      name: String
      reviewCount: Int
      friends: [User]
      email: String @private(scope: "loggedIn")
    }

    You can select the definition of the private directive and its arguments (with @private and @private(scope:) respectively), but you cannot select the application of the @private on User.email.

    For the stated use cases of this RFC, it is more likely that consumers want to select and track usage and changes to the definition of the custom directive instead.

    If we did want to support this, a syntax such as User.email@private[0] could work. (The indexing is necessary since multiple applications of the same directive is allowed, and each is considered unique.)

  • Union members

    This spec does not support selecting members inside a union definition.

    For example:

    type Breakfast {
      eggCount: Int
    }

    type Lunch {
      sandwichFilling: String
    }

    union Meal = Breakfast | Lunch

    You may select the Meal definition (as "Meal"), but you may not select members on Meal (e.g. Meal.Breakfast or Meal.Lunch).

    It is unclear what the use case for this would be, so we won't (yet?) support this. In such cases, consumers may select type members directly (e.g. Lunch).

Answered questions​

  • Would we want to add a method to graphql-js? A fieldCoordinateToFieldNode method (for example) may take in a field coordinate string and return a field AST node to serve as a helper / reference implementation of the algorithm to look up the field node.

    Update: This was discussed in the August Working Group Meeting - it was suggested to keep any utilities as third party libraries to avoid edge ambiguity problems, and to be able to iterate faster.