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Type System

The GraphQL Type system describes the capabilities of a GraphQL server and is used to determine if a query is valid. The type system also describes the input types of query variables to determine if values provided at runtime are valid.

A GraphQL server's capabilities are referred to as that server's "schema". A schema is defined in terms of the types and directives it supports.

A given GraphQL schema must itself be internally valid. This section describes the rules for this validation process where relevant.

A GraphQL schema is represented by a root type for each kind of operation: query, mutation, and subscription; this determines the place in the type system where those operations begin.

All types within a GraphQL schema must have unique names. No two provided types may have the same name. No provided type may have a name which conflicts with any built in types (including Scalar and Introspection types).

All directives within a GraphQL schema must have unique names. A directive and a type may share the same name, since there is no ambiguity between them.

All types and directives defined within a schema must not have a name which begins with {"__"} (two underscores), as this is used exclusively by GraphQL's introspection system.

Types

The fundamental unit of any GraphQL Schema is the type. There are nine kinds of types in GraphQL.

The most basic type is a Scalar. A scalar represents a primitive value, like a string or an integer. Oftentimes, the possible responses for a scalar field are enumerable. GraphQL offers an Enum type in those cases, where the type specifies the space of valid responses.

Scalars and Enums form the leaves in response trees; the intermediate levels are Object types, which define a set of fields, where each field is another type in the system, allowing the definition of arbitrary type hierarchies.

GraphQL supports three abstract types: interfaces, unions, and inputUnions.

An Interface defines a list of fields; Object types that implement that interface are guaranteed to implement those fields. Whenever the type system claims it will return an interface, it will return a valid implementing type.

A Union defines a list of possible types; similar to interfaces, whenever the type system claims a union will be returned, one of the possible types will be returned.

An Input Union defines a list of possible Input Object types; Input Union types are fulfilled by a single member Input Object.

All of the types so far are assumed to be both nullable and singular: e.g. a scalar string returns either null or a singular string. The type system might want to define that it returns a list of other types; the List type is provided for this reason, and wraps another type. Similarly, the Non-Null type wraps another type, and denotes that the result will never be null. These two types are referred to as "wrapping types"; non-wrapping types are referred to as "base types". A wrapping type has an underlying "base type", found by continually unwrapping the type until a base type is found.

Finally, oftentimes it is useful to provide complex structs as inputs to GraphQL queries; the Input Object type allows the schema to define exactly what data is expected from the client in these queries.

Scalars

As expected by the name, a scalar represents a primitive value in GraphQL. GraphQL responses take the form of a hierarchical tree; the leaves on these trees are GraphQL scalars.

All GraphQL scalars are representable as strings, though depending on the response format being used, there may be a more appropriate primitive for the given scalar type, and server should use those types when appropriate.

GraphQL provides a number of built-in scalars, but type systems can add additional scalars with semantic meaning. For example, a GraphQL system could define a scalar called Time which, while serialized as a string, promises to conform to ISO-8601. When querying a field of type Time, you can then rely on the ability to parse the result with an ISO-8601 parser and use a client-specific primitive for time. Another example of a potentially useful custom scalar is Url, which serializes as a string, but is guaranteed by the server to be a valid URL.

A server may omit any of the built-in scalars from its schema, for example if a schema does not refer to a floating-point number, then it will not include the Float type. However, if a schema includes a type with the name of one of the types described here, it must adhere to the behavior described. As an example, a server must not include a type called Int and use it to represent 128-bit numbers, or internationalization information.

Result Coercion

A GraphQL server, when preparing a field of a given scalar type, must uphold the contract the scalar type describes, either by coercing the value or producing an error.

For example, a GraphQL server could be preparing a field with the scalar type Int and encounter a floating-point number. Since the server must not break the contract by yielding a non-integer, the server should truncate the fractional value and only yield the integer value. If the server encountered a boolean true value, it should return 1. If the server encountered a string, it may attempt to parse the string for a base-10 integer value. If the server encounters some value that cannot be reasonably coerced to an Int, then it must raise a field error.

Since this coercion behavior is not observable to clients of the GraphQL server, the precise rules of coercion are left to the implementation. The only requirement is that the server must yield values which adhere to the expected Scalar type.

Input Coercion

If a GraphQL server expects a scalar type as input to an argument, coercion is observable and the rules must be well defined. If an input value does not match a coercion rule, a query error must be raised.

GraphQL has different constant literals to represent integer and floating-point input values, and coercion rules may apply differently depending on which type of input value is encountered. GraphQL may be parameterized by query variables, the values of which are often serialized when sent over a transport like HTTP. Since some common serializations (ex. JSON) do not discriminate between integer and floating-point values, they are interpreted as an integer input value if they have an empty fractional part (ex. 1.0) and otherwise as floating-point input value.

For all types below, with the exception of Non-Null, if the explicit value {null} is provided, then the result of input coercion is {null}.

Built-in Scalars

GraphQL provides a basic set of well-defined Scalar types. A GraphQL server should support all of these types, and a GraphQL server which provide a type by these names must adhere to the behavior described below.

Int

The Int scalar type represents a signed 32-bit numeric non-fractional value. Response formats that support a 32-bit integer or a number type should use that type to represent this scalar.

Result Coercion

GraphQL servers should coerce non-int raw values to Int when possible otherwise they must raise a field error. Examples of this may include returning 1 for the floating-point number 1.0, or 2 for the string "2".

Input Coercion

When expected as an input type, only integer input values are accepted. All other input values, including strings with numeric content, must raise a query error indicating an incorrect type. If the integer input value represents a value less than -231 or greater than or equal to 231, a query error should be raised.

Note: Numeric integer values larger than 32-bit should either use String or a custom-defined Scalar type, as not all platforms and transports support encoding integer numbers larger than 32-bit.

Float

The Float scalar type represents signed double-precision fractional values as specified by IEEE 754. Response formats that support an appropriate double-precision number type should use that type to represent this scalar.

Result Coercion

GraphQL servers should coerce non-floating-point raw values to Float when possible otherwise they must raise a field error. Examples of this may include returning 1.0 for the integer number 1, or 2.0 for the string "2".

Input Coercion

When expected as an input type, both integer and float input values are accepted. Integer input values are coerced to Float by adding an empty fractional part, for example 1.0 for the integer input value 1. All other input values, including strings with numeric content, must raise a query error indicating an incorrect type. If the integer input value represents a value not representable by IEEE 754, a query error should be raised.

String

The String scalar type represents textual data, represented as UTF-8 character sequences. The String type is most often used by GraphQL to represent free-form human-readable text. All response formats must support string representations, and that representation must be used here.

Result Coercion

GraphQL servers should coerce non-string raw values to String when possible otherwise they must raise a field error. Examples of this may include returning the string "true" for a boolean true value, or the string "1" for the integer 1.

Input Coercion

When expected as an input type, only valid UTF-8 string input values are accepted. All other input values must raise a query error indicating an incorrect type.

Boolean

The Boolean scalar type represents true or false. Response formats should use a built-in boolean type if supported; otherwise, they should use their representation of the integers 1 and 0.

Result Coercion

GraphQL servers should coerce non-boolean raw values to Boolean when possible otherwise they must raise a field error. Examples of this may include returning true for any non-zero number.

Input Coercion

When expected as an input type, only boolean input values are accepted. All other input values must raise a query error indicating an incorrect type.

ID

The ID scalar type represents a unique identifier, often used to refetch an object or as the key for a cache. The ID type is serialized in the same way as a String; however, it is not intended to be human-readable. While it is often numeric, it should always serialize as a String.

Result Coercion

GraphQL is agnostic to ID format, and serializes to string to ensure consistency across many formats ID could represent, from small auto-increment numbers, to large 128-bit random numbers, to base64 encoded values, or string values of a format like GUID.

GraphQL servers should coerce as appropriate given the ID formats they expect. When coercion is not possible they must raise a field error.

Input Coercion

When expected as an input type, any string (such as "4") or integer (such as 4) input value should be coerced to ID as appropriate for the ID formats a given GraphQL server expects. Any other input value, including float input values (such as 4.0), must raise a query error indicating an incorrect type.

Objects

GraphQL queries are hierarchical and composed, describing a tree of information. While Scalar types describe the leaf values of these hierarchical queries, Objects describe the intermediate levels.

GraphQL Objects represent a list of named fields, each of which yield a value of a specific type. Object values should be serialized as ordered maps, where the queried field names (or aliases) are the keys and the result of evaluating the field is the value, ordered by the order in which they appear in the query.

All fields defined within an Object type must not have a name which begins with {"__"} (two underscores), as this is used exclusively by GraphQL's introspection system.

For example, a type Person could be described as:

type Person {
  name: String
  age: Int
  picture: Url
}

Where name is a field that will yield a String value, and age is a field that will yield an Int value, and picture is a field that will yield a Url value.

A query of an object value must select at least one field. This selection of fields will yield an ordered map containing exactly the subset of the object queried, which should be represented in the order in which they were queried. Only fields that are declared on the object type may validly be queried on that object.

For example, selecting all the fields of Person:

{
  name
  age
  picture
}

Would yield the object:

{
  "name": "Mark Zuckerberg",
  "age": 30,
  "picture": "http://some.cdn/picture.jpg"
}

While selecting a subset of fields:

{
  age
  name
}

Must only yield exactly that subset:

{
  "age": 30,
  "name": "Mark Zuckerberg"
}

A field of an Object type may be a Scalar, Enum, another Object type, an Interface, or a Union. Additionally, it may be any wrapping type whose underlying base type is one of those five.

For example, the Person type might include a relationship:

type Person {
  name: String
  age: Int
  picture: Url
  relationship: Person
}

Valid queries must supply a nested field set for a field that returns an object, so this query is not valid:

{
  name
  relationship
}

However, this example is valid:

{
  name
  relationship {
    name
  }
}

And will yield the subset of each object type queried:

{
  "name": "Mark Zuckerberg",
  "relationship": {
    "name": "Priscilla Chan"
  }
}

Field Ordering

When querying an Object, the resulting mapping of fields are conceptually ordered in the same order in which they were encountered during query execution, excluding fragments for which the type does not apply and fields or fragments that are skipped via @skip or @include directives. This ordering is correctly produced when using the {CollectFields()} algorithm.

Response serialization formats capable of representing ordered maps should maintain this ordering. Serialization formats which can only represent unordered maps (such as JSON) should retain this order textually. That is, if two fields {foo, bar} were queried in that order, the resulting JSON serialization should contain {"foo": "...", "bar": "..."} in the same order.

Producing a response where fields are represented in the same order in which they appear in the request improves human readability during debugging and enables more efficient parsing of responses if the order of properties can be anticipated.

If a fragment is spread before other fields, the fields that fragment specifies occur in the response before the following fields.

{
  foo
  ...Frag
  qux
}

fragment Frag on Query {
  bar
  baz
}

Produces the ordered result:

{
  "foo": 1,
  "bar": 2,
  "baz": 3,
  "qux": 4
}

If a field is queried multiple times in a selection, it is ordered by the first time it is encountered. However fragments for which the type does not apply does not affect ordering.

{
  foo
  ...Ignored
  ...Matching
  bar
}

fragment Ignored on UnknownType {
  qux
  baz
}

fragment Matching on Query {
  bar
  qux
  foo
}

Produces the ordered result:

{
  "foo": 1,
  "bar": 2,
  "qux": 3
}

Also, if directives result in fields being excluded, they are not considered in the ordering of fields.

{
  foo @skip(if: true)
  bar
  foo
}

Produces the ordered result:

{
  "bar": 1,
  "foo": 2
}

Result Coercion

Determining the result of coercing an object is the heart of the GraphQL executor, so this is covered in that section of the spec.

Input Coercion

Objects are never valid inputs.

Object Field Arguments

Object fields are conceptually functions which yield values. Occasionally object fields can accept arguments to further specify the return value. Object field arguments are defined as a list of all possible argument names and their expected input types.

All arguments defined within a field must not have a name which begins with {"__"} (two underscores), as this is used exclusively by GraphQL's introspection system.

For example, a Person type with a picture field could accept an argument to determine what size of an image to return.

type Person {
  name: String
  picture(size: Int): Url
}

GraphQL queries can optionally specify arguments to their fields to provide these arguments.

This example query:

{
  name
  picture(size: 600)
}

May yield the result:

{
  "name": "Mark Zuckerberg",
  "picture": "http://some.cdn/picture_600.jpg"
}

The type of an object field argument can be any Input type.

Object Field deprecation

Fields in an object may be marked as deprecated as deemed necessary by the application. It is still legal to query for these fields (to ensure existing clients are not broken by the change), but the fields should be appropriately treated in documentation and tooling.

Object type validation

Object types have the potential to be invalid if incorrectly defined. This set of rules must be adhered to by every Object type in a GraphQL schema.

  1. An Object type must define one or more fields.
  2. The fields of an Object type must have unique names within that Object type; no two fields may share the same name.
  3. Each field of an Object type must not have a name which begins with the characters {"__"} (two underscores).
  4. An object type may declare that it implements one or more unique interfaces.
  5. An object type must be a super-set of all interfaces it implements:
    1. The object type must include a field of the same name for every field defined in an interface.
      1. The object field must be of a type which is equal to or a sub-type of the interface field (covariant).
        1. An object field type is a valid sub-type if it is equal to (the same type as) the interface field type.
        2. An object field type is a valid sub-type if it is an Object type and the interface field type is either an Interface type or a Union type and the object field type is a possible type of the interface field type.
        3. An object field type is a valid sub-type if it is a List type and the interface field type is also a List type and the list-item type of the object field type is a valid sub-type of the list-item type of the interface field type.
        4. An object field type is a valid sub-type if it is a Non-Null variant of a valid sub-type of the interface field type.
      2. The object field must include an argument of the same name for every argument defined in the interface field.
        1. The object field argument must accept the same type (invariant) as the interface field argument.
      3. The object field may include additional arguments not defined in the interface field, but any additional argument must not be required.

Interfaces

GraphQL Interfaces represent a list of named fields and their arguments. GraphQL objects can then implement an interface, which guarantees that they will contain the specified fields.

Fields on a GraphQL interface have the same rules as fields on a GraphQL object; their type can be Scalar, Object, Enum, Interface, or Union, or any wrapping type whose base type is one of those five.

For example, an interface may describe a required field and types such as Person or Business may then implement this interface.

interface NamedEntity {
  name: String
}

type Person implements NamedEntity {
  name: String
  age: Int
}

type Business implements NamedEntity {
  name: String
  employeeCount: Int
}

Fields which yield an interface are useful when one of many Object types are expected, but some fields should be guaranteed.

To continue the example, a Contact might refer to NamedEntity.

type Contact {
  entity: NamedEntity
  phoneNumber: String
  address: String
}

This allows us to write a query for a Contact that can select the common fields.

{
  entity {
    name
  }
  phoneNumber
}

When querying for fields on an interface type, only those fields declared on the interface may be queried. In the above example, entity returns a NamedEntity, and name is defined on NamedEntity, so it is valid. However, the following would not be a valid query:

{
  entity {
    name
    age
  }
  phoneNumber
}

because entity refers to a NamedEntity, and age is not defined on that interface. Querying for age is only valid when the result of entity is a Person; the query can express this using a fragment or an inline fragment:

{
  entity {
    name
    ... on Person {
      age
    }
  },
  phoneNumber
}

Result Coercion

The interface type should have some way of determining which object a given result corresponds to. Once it has done so, the result coercion of the interface is the same as the result coercion of the object.

Input Coercion

Interfaces are never valid inputs.

Interface type validation

Interface types have the potential to be invalid if incorrectly defined.

  1. An Interface type must define one or more fields.
  2. The fields of an Interface type must have unique names within that Interface type; no two fields may share the same name.
  3. Each field of an Interface type must not have a name which begins with the characters {"__"} (two underscores).

Unions

GraphQL Unions represent an object that could be one of a list of GraphQL Object types, but provides for no guaranteed fields between those types. They also differ from interfaces in that Object types declare what interfaces they implement, but are not aware of what unions contain them.

With interfaces and objects, only those fields defined on the type can be queried directly; to query other fields on an interface, typed fragments must be used. This is the same as for unions, but unions do not define any fields, so no fields may be queried on this type without the use of typed fragments.

For example, we might have the following type system:

union SearchResult = Photo | Person

type Person {
  name: String
  age: Int
}

type Photo {
  height: Int
  width: Int
}

type SearchQuery {
  firstSearchResult: SearchResult
}

When querying the firstSearchResult field of type SearchQuery, the query would ask for all fields inside of a fragment indicating the appropriate type. If the query wanted the name if the result was a Person, and the height if it was a photo, the following query is invalid, because the union itself defines no fields:

{
  firstSearchResult {
    name
    height
  }
}

Instead, the query would be:

{
  firstSearchResult {
    ... on Person {
      name
    }
    ... on Photo {
      height
    }
  }
}

Result Coercion

The union type should have some way of determining which object a given result corresponds to. Once it has done so, the result coercion of the union is the same as the result coercion of the object.

Input Coercion

Unions are never valid inputs.

Union type validation

Union types have the potential to be invalid if incorrectly defined.

  1. The member types of a Union type must all be Object base types; Scalar, Interface and Union types may not be member types of a Union. Similarly, wrapping types may not be member types of a Union.
  2. A Union type must define one or more unique member types.

Enums

GraphQL Enums are a variant on the Scalar type, which represents one of a finite set of possible values.

GraphQL Enums are not references for a numeric value, but are unique values in their own right. They serialize as a string: the name of the represented value.

Result Coercion

GraphQL servers must return one of the defined set of possible values. If a reasonable coercion is not possible they must raise a field error.

Input Coercion

GraphQL has a constant literal to represent enum input values. GraphQL string literals must not be accepted as an enum input and instead raise a query error.

Query variable transport serializations which have a different representation for non-string symbolic values (for example, EDN) should only allow such values as enum input values. Otherwise, for most transport serializations that do not, strings may be interpreted as the enum input value with the same name.

Input Objects

Fields can define arguments that the client passes up with the query, to configure their behavior. These inputs can be Strings or Enums, but they sometimes need to be more complex than this.

The Object type defined above is inappropriate for re-use here, because Objects can contain fields that express circular references or references to interfaces and unions, neither of which is appropriate for use as an input argument. For this reason, input objects have a separate type in the system.

An Input Object defines a set of input fields; the input fields are either scalars, enums, input unions, or other input objects. This allows arguments to accept arbitrarily complex structs.

Result Coercion

An input object is never a valid result.

Input Coercion

The value for an input object should be an input object literal or an unordered map supplied by a variable, otherwise an error should be thrown. In either case, the input object literal or unordered map should not contain any entries with names not defined by a field of this input object type, otherwise an error should be thrown.

The result of coercion is an unordered map with an entry for each field both defined by the input object type and provided with a value. If the value {null} was provided, an entry in the coerced unordered map must exist for that field. In other words, there is a semantic difference between the explicitly provided value {null} versus having not provided a value.

The value of each entry in the coerced unordered map is the result of input coercion of the value provided for that field for the type of the field defined by the input object type

Any non-nullable field defined by the input object type which does not have a corresponding entry in the original value, or is represented by a variable which was not provided a value, or for which the value {null} was provided, an error should be thrown.

Following are examples of input coercion for an input object type with a String field a and a required (non-null) Int! field b:

input ExampleInputObject {
  a: String
  b: Int!
}
Literal Value Variables Coerced Value
{ a: "abc", b: 123 } {} { a: "abc", b: 123 }
{ a: null, b: 123 } {} { a: null, b: 123 }
{ b: 123 } {} { b: 123 }
{ a: $var, b: 123 } { var: null } { a: null, b: 123 }
{ a: $var, b: 123 } {} { b: 123 }
{ b: $var } { var: 123 } { b: 123 }
$var { var: { b: 123 } } { b: 123 }
"abc123" {} Error: Incorrect value
$var { var: "abc123" } } Error: Incorrect value
{ a: "abc", b: "123" } {} Error: Incorrect value for field {b}
{ a: "abc" } {} Error: Missing required field {b}
{ b: $var } {} Error: Missing required field {b}.
$var { var: { a: "abc" } } Error: Missing required field {b}
{ a: "abc", b: null } {} Error: {b} must be non-null.
{ b: $var } { var: null } Error: {b} must be non-null.
{ b: 123, c: "xyz" } {} Error: Unexpected field {c}

Input Object type validation

  1. An Input Object type must define one or more fields.
  2. The fields of an Input Object type must have unique names within that Input Object type; no two fields may share the same name.
  3. The return types of each defined field must be an Input type.

Input Unions

GraphQL Input Unions represent an argument that could be one of a list of GraphQL Input Object types, determined at execution.

The Union type defined above is inappropriate for re-use here, because a Union contains Object types. Object types are not permitted as inputs, and Input Object types are not permitted in query results so these types should be grouped separately.

Input Union types may also be used as values for input objects, allowing for arbitrarily nested structs. In order to determine the concrete Object type fulfilling the Input Union, the __inputname field must be specified as a member of the input object. This field value must be a string representing a type name of the Input Object which is both a member of the Input Union and is fulfilled by the fields of the input.

For example, we might have the following type system:

inputUnion ContentBlock = ParagraphInput | PhotoInput

input ParagraphInput {
  text: String
}

type PhotoInput {
  image: String!
  title: String!
}

type Mutation {
  createPost(content: [ContentBlock]!): Post
}

When executing the createPost mutation, the mutation accepts the input union ContentBlock, and the values provided must both be a member of the input union and specify which input object type it is fulfilling.

Examples of valid input:

[
  {__inputname: "ParagraphInput", text: "This is a block of text" },
  {__inputname: "PhotoInput", image: "http://example.com/image.png", title: "Example Image"},
  {__inputname: "ParagraphInput", text: "This is a block of after the photo" },
]

{__inputname: "ParagraphInput", text: "This is a block of text with a single member" }

And invalid inputs:

[
  {text: "invalid:, __inputname is not specified"}
]
[
  {
    __inputname: "PhotoInput",
    text: "invalid: text is not a member of input",
    image: "http://example.com/error.png",
    title: "Error Image"
  }
]

Result Coercion

An input object is never a valid result.

Input Coercion

The value for an input union should be an input object literal or an unordered map supplied by a variable, otherwise an error should be thrown. The input object literal must contain a property __inputname with a string value of the name of the input object member of the input union, otherwise an error should be throw. All other fields must be valid in fulfilling the input object represented by the __inputname as defined in Input Object coercion.

The result of coercion is that of a standard input object coercion, with an additional field __inputname containing the name of the type fulfilling the input union.

Input Union type validation

Input Union types have the potential to be invalid if incorrectly defined.

  1. The member types of an Input Union type must all be Input Object base types; Scalar, Interface and Input Union types may not be member types of an Input Union. Similarly, wrapping types may not be member types of a Union.
  2. An Input Union type must define one or more unique member types.

Lists

A GraphQL list is a special collection type which declares the type of each item in the List (referred to as the item type of the list). List values are serialized as ordered lists, where each item in the list is serialized as per the item type. To denote that a field uses a List type the item type is wrapped in square brackets like this: pets: [Pet].

Result Coercion

GraphQL servers must return an ordered list as the result of a list type. Each item in the list must be the result of a result coercion of the item type. If a reasonable coercion is not possible they must raise a field error. In particular, if a non-list is returned, the coercion should fail, as this indicates a mismatch in expectations between the type system and the implementation.

Input Coercion

When expected as an input, list values are accepted only when each item in the list can be accepted by the list's item type.

If the value passed as an input to a list type is not a list and not the {null} value, it should be coerced as though the input was a list of size one, where the value passed is the only item in the list. This is to allow inputs that accept a "var args" to declare their input type as a list; if only one argument is passed (a common case), the client can just pass that value rather than constructing the list.

Note that when a {null} value is provided via a runtime variable value for a list type, the value is interpreted as no list being provided, and not a list of size one with the value {null}.

Non-Null

By default, all types in GraphQL are nullable; the {null} value is a valid response for all of the above types. To declare a type that disallows null, the GraphQL Non-Null type can be used. This type wraps an underlying type, and this type acts identically to that wrapped type, with the exception that {null} is not a valid response for the wrapping type. A trailing exclamation mark is used to denote a field that uses a Non-Null type like this: name: String!.

Nullable vs. Optional

Fields are always optional within the context of a query, a field may be omitted and the query is still valid. However fields that return Non-Null types will never return the value {null} if queried.

Inputs (such as field arguments), are always optional by default. However a non-null input type is required. In addition to not accepting the value {null}, it also does not accept omission. For the sake of simplicity nullable types are always optional and non-null types are always required.

Result Coercion

In all of the above result coercions, {null} was considered a valid value. To coerce the result of a Non-Null type, the coercion of the wrapped type should be performed. If that result was not {null}, then the result of coercing the Non-Null type is that result. If that result was {null}, then a field error must be raised.

Input Coercion

If an argument or input-object field of a Non-Null type is not provided, is provided with the literal value {null}, or is provided with a variable that was either not provided a value at runtime, or was provided the value {null}, then a query error must be raised.

If the value provided to the Non-Null type is provided with a literal value other than {null}, or a Non-Null variable value, it is coerced using the input coercion for the wrapped type.

Example: A non-null argument cannot be omitted.

{
  fieldWithNonNullArg
}

Example: The value {null} cannot be provided to a non-null argument.

{
  fieldWithNonNullArg(nonNullArg: null)
}

Example: A variable of a nullable type cannot be provided to a non-null argument.

query withNullableVariable($var: String) {
  fieldWithNonNullArg(nonNullArg: $var)
}

Note: The Validation section defines providing a nullable variable type to a non-null input type as invalid.

Non-Null type validation

  1. A Non-Null type must not wrap another Non-Null type.

Directives

A GraphQL schema includes a list of the directives the execution engine supports.

GraphQL implementations should provide the @skip and @include directives.

@skip

The @skip directive may be provided for fields, fragment spreads, and inline fragments, and allows for conditional exclusion during execution as described by the if argument.

In this example experimentalField will only be queried if the variable $someTest has the value false.

query myQuery($someTest: Boolean) {
  experimentalField @skip(if: $someTest)
}

@include

The @include directive may be provided for fields, fragment spreads, and inline fragments, and allows for conditional inclusion during execution as described by the if argument.

In this example experimentalField will only be queried if the variable $someTest has the value true

query myQuery($someTest: Boolean) {
  experimentalField @include(if: $someTest)
}

Note: Neither @skip nor @include has precedence over the other. In the case that both the @skip and @include directives are provided in on the same the field or fragment, it must be queried only if the @skip condition is false and the @include condition is true. Stated conversely, the field or fragment must not be queried if either the @skip condition is true or the @include condition is false.

Initial types

A GraphQL schema includes types, indicating where query, mutation, and subscription operations start. This provides the initial entry points into the type system. The query type must always be provided, and is an Object base type. The mutation type is optional; if it is not provided, that means the system does not support mutations. If it is provided, it must be an object base type. Similarly, the subscription type is optional; if it is not provided, the system does not support subscriptions. If it is provided, it must be an object base type.

The fields on the query type indicate what fields are available at the top level of a GraphQL query. For example, a basic GraphQL query like this one:

query getMe {
  me
}

Is valid when the type provided for the query starting type has a field named "me". Similarly

mutation setName {
  setName(name: "Zuck") {
    newName
  }
}

Is valid when the type provided for the mutation starting type is not null, and has a field named "setName" with a string argument named "name".

subscription {
  newMessage {
    text
  }
}

Is valid when the type provided for the subscription starting type is not null, and has a field named "newMessage" and only contains a single root field.