Implement OneOf Input Objects via @oneOf directive

src/__testUtils__/kitchenSinkSDL.ts

@@ -27,6 +27,7 @@ type Foo implements Bar & Baz & Two {
   five(argument: [String] = ["string", "string"]): String
   six(argument: InputType = {key: "value"}): Type
   seven(argument: Int = null): Type
+  eight(argument: OneOfInputType): Type
 }
 
 type AnnotatedObject @onObject(arg: "value") {
@@ -116,6 +117,11 @@ input InputType {
   answer: Int = 42
 }
 
+input OneOfInputType @oneOf {
+  string: String
+  int: Int
+}
+
 input AnnotatedInput @onInputObject {
   annotatedField: Type @onInputFieldDefinition
 }

src/execution/__tests__/oneof-test.ts

@@ -0,0 +1,185 @@
+import { describe, it } from 'mocha';
+
+import { expectJSON } from '../../__testUtils__/expectJSON.js';
+
+import { parse } from '../../language/parser.js';
+
+import { buildSchema } from '../../utilities/buildASTSchema.js';
+
+import type { ExecutionResult } from '../execute.js';
+import { execute } from '../execute.js';
+
+const schema = buildSchema(`
+  type Query {
+    test(input: TestInputObject!): TestObject
+  }
+
+  input TestInputObject @oneOf {
+    a: String
+    b: Int
+  }
+
+  type TestObject {
+    a: String
+    b: Int
+  }
+`);
+
+function executeQuery(
+  query: string,
+  rootValue: unknown,
+  variableValues?: { [variable: string]: unknown },
+): ExecutionResult | Promise<ExecutionResult> {
+  return execute({ schema, document: parse(query), rootValue, variableValues });
+}
+
+describe('Execute: Handles OneOf Input Objects', () => {
+  describe('OneOf Input Objects', () => {
+    const rootValue = {
+      test({ input }: { input: { a?: string; b?: number } }) {
+        return input;
+      },
+    };
+
+    it('accepts a good default value', () => {
+      const query = `
+        query ($input: TestInputObject! = {a: "abc"}) {
+          test(input: $input) {
+            a
+            b
+          }
+        }
+      `;
+      const result = executeQuery(query, rootValue);
+
+      expectJSON(result).toDeepEqual({
+        data: {
+          test: {
+            a: 'abc',
+            b: null,
+          },
+        },
+      });
+    });
+
+    it('rejects a bad default value', () => {
+      const query = `
+        query ($input: TestInputObject! = {a: "abc", b: 123}) {
+          test(input: $input) {
+            a
+            b
+          }
+        }
+      `;
+      const result = executeQuery(query, rootValue);
+
+      expectJSON(result).toDeepEqual({
+        data: {
+          test: null,
+        },
+        errors: [
+          {
+            locations: [{ column: 23, line: 3 }],
+            message:
+              // This type of error would be caught at validation-time
+              // hence the vague error message here.
+              'Argument "input" of non-null type "TestInputObject!" must not be null.',
+            path: ['test'],
+          },
+        ],
+      });
+    });
+
+    it('accepts a good variable', () => {
+      const query = `
+        query ($input: TestInputObject!) {
+          test(input: $input) {
+            a
+            b
+          }
+        }
+      `;
+      const result = executeQuery(query, rootValue, { input: { a: 'abc' } });
+
+      expectJSON(result).toDeepEqual({
+        data: {
+          test: {
+            a: 'abc',
+            b: null,
+          },
+        },
+      });
+    });
+
+    it('accepts a good variable with an undefined key', () => {
+      const query = `
+        query ($input: TestInputObject!) {
+          test(input: $input) {
+            a
+            b
+          }
+        }
+      `;
+      const result = executeQuery(query, rootValue, {
+        input: { a: 'abc', b: undefined },
+      });
+
+      expectJSON(result).toDeepEqual({
+        data: {
+          test: {
+            a: 'abc',
+            b: null,
+          },
+        },
+      });
+    });
+
+    it('rejects a variable with multiple non-null keys', () => {
+      const query = `
+        query ($input: TestInputObject!) {
+          test(input: $input) {
+            a
+            b
+          }
+        }
+      `;
+      const result = executeQuery(query, rootValue, {
+        input: { a: 'abc', b: 123 },
+      });
+
+      expectJSON(result).toDeepEqual({
+        errors: [
+          {
+            locations: [{ column: 16, line: 2 }],
+            message:
+              'Variable "$input" got invalid value { a: "abc", b: 123 }; Exactly one key must be specified for OneOf type "TestInputObject".',
+          },
+        ],
+      });
+    });
+
+    it('rejects a variable with multiple nullable keys', () => {
+      const query = `
+        query ($input: TestInputObject!) {
+          test(input: $input) {
+            a
+            b
+          }
+        }
+      `;
+      const result = executeQuery(query, rootValue, {
+        input: { a: 'abc', b: null },
+      });
+
+      expectJSON(result).toDeepEqual({
+        errors: [
+          {
+            locations: [{ column: 16, line: 2 }],
+            message:
+              'Variable "$input" got invalid value { a: "abc", b: null }; Exactly one key must be specified for OneOf type "TestInputObject".',
+          },
+        ],
+      });
+    });
+  });
+});

src/index.ts

@@ -66,6 +66,7 @@ export {
   GraphQLStreamDirective,
   GraphQLDeprecatedDirective,
   GraphQLSpecifiedByDirective,
+  GraphQLOneOfDirective,
   // "Enum" of Type Kinds
   TypeKind,
   // Constant Deprecation Reason

src/language/__tests__/schema-printer-test.ts

@@ -61,6 +61,7 @@ describe('Printer: SDL document', () => {
         five(argument: [String] = ["string", "string"]): String
         six(argument: InputType = { key: "value" }): Type
         seven(argument: Int = null): Type
+        eight(argument: OneOfInputType): Type
       }
 
       type AnnotatedObject @onObject(arg: "value") {
@@ -143,6 +144,11 @@ describe('Printer: SDL document', () => {
         answer: Int = 42
       }
 
+      input OneOfInputType @oneOf {
+        string: String
+        int: Int
+      }
+
       input AnnotatedInput @onInputObject {
         annotatedField: Type @onInputFieldDefinition
       }

src/type/__tests__/introspection-test.ts

@@ -372,6 +372,17 @@ describe('Introspection', () => {
                   isDeprecated: false,
                   deprecationReason: null,
                 },
+                {
+                  name: 'isOneOf',
+                  args: [],
+                  type: {
+                    kind: 'SCALAR',
+                    name: 'Boolean',
+                    ofType: null,
+                  },
+                  isDeprecated: false,
+                  deprecationReason: null,
+                },
               ],
               inputFields: null,
               interfaces: [],
@@ -989,6 +1000,12 @@ describe('Introspection', () => {
                 },
               ],
             },
+            {
+              name: 'oneOf',
+              isRepeatable: false,
+              locations: ['INPUT_OBJECT'],
+              args: [],
+            },
           ],
         },
       },
@@ -1519,6 +1536,95 @@ describe('Introspection', () => {
     });
   });
 
+  it('identifies oneOf for input objects', () => {
+    const schema = buildSchema(`
+      input SomeInputObject @oneOf {
+        a: String
+      }
+
+      input AnotherInputObject {
+        a: String
+        b: String
+      }
+
+      type Query {
+        someField(someArg: SomeInputObject): String
+        anotherField(anotherArg: AnotherInputObject): String
+      }
+    `);
+
+    const source = `
+      {
+        oneOfInputObject: __type(name: "SomeInputObject") {
+          isOneOf
+        }
+        inputObject: __type(name: "AnotherInputObject") {
+          isOneOf
+        }
+      }
+    `;
+
+    expect(graphqlSync({ schema, source })).to.deep.equal({
+      data: {
+        oneOfInputObject: {
+          isOneOf: true,
+        },
+        inputObject: {
+          isOneOf: false,
+        },
+      },
+    });
+  });
+
+  it('returns null for oneOf for other types', () => {
+    const schema = buildSchema(`
+      type SomeObject implements SomeInterface {
+        fieldA: String
+      }
+      enum SomeEnum {
+        SomeObject
+      }
+      interface SomeInterface {
+        fieldA: String
+      }
+      union SomeUnion = SomeObject
+      type Query {
+        someField(enum: SomeEnum): SomeUnion
+        anotherField(enum: SomeEnum): SomeInterface
+      }
+    `);
+
+    const source = `
+      {
+        object: __type(name: "SomeObject") {
+          isOneOf
+        }
+        enum: __type(name: "SomeEnum") {
+          isOneOf
+        }
+        interface: __type(name: "SomeInterface") {
+          isOneOf
+        }
+        scalar: __type(name: "String") {
+          isOneOf
+        }
+        union: __type(name: "SomeUnion") {
+          isOneOf
+        }
+      }
+    `;
+
+    expect(graphqlSync({ schema, source })).to.deep.equal({
+      data: {
+        object: { isOneOf: null },
+        enum: { isOneOf: null },
+        interface: { isOneOf: null },
+        scalar: { isOneOf: null },
+        union: { isOneOf: null },
+      },
+    });
+  });
+
   it('fails as expected on the __type root field without an arg', () => {
     const schema = buildSchema(`
       type Query {