Transform interfaces into possible types only

packages/apollo-gateway/src/FieldSet.ts

@@ -14,6 +14,7 @@ export interface Field<TParent = GraphQLCompositeType> {
   parentType: TParent;
   fieldNode: FieldNode;
   fieldDef: GraphQLField<any, any>;
+  parentTypesArray?: TParent[];
 }
 export type FieldSet = Field[];
 

packages/apollo-gateway/src/__tests__/__fixtures__/schemas/product.ts

@@ -24,6 +24,21 @@ export const typeDefs = gql`
     sku: String!
     name: String
     price: String
+    details: ProductDetails
+  }
+
+  interface ProductDetails {
+    country: String
+  }
+
+  type ProductDetailsFurniture implements ProductDetails {
+    country: String
+    color: String
+  }
+
+  type ProductDetailsBook implements ProductDetails {
+    country: String
+    pages: Int
   }
 
   type Furniture implements Product @key(fields: "upc") @key(fields: "sku") {
@@ -33,6 +48,7 @@ export const typeDefs = gql`
     price: String
     brand: Brand
     metadata: [MetadataOrError]
+    details: ProductDetailsFurniture
   }
 
   extend type Book implements Product @key(fields: "isbn") {
@@ -43,6 +59,7 @@ export const typeDefs = gql`
     sku: String!
     name(delimeter: String = " "): String @requires(fields: "title year")
     price: String
+    details: ProductDetailsBook
   }
 
   type Car @key(fields: "id") {

packages/apollo-gateway/src/__tests__/buildQueryPlan.test.ts

@@ -790,4 +790,91 @@ describe('buildQueryPlan', () => {
       }
     `);
   });
+
+  it(`interface fragments should expand into possible types only`, () => {
+    const query = gql`
+      query {
+        books {
+          ... on Product {
+            name
+            ... on Furniture {
+              upc
+            }
+          }
+        }
+      }
+    `;
+
+    const queryPlan = buildQueryPlan(buildOperationContext(schema, query));
+
+    expect(queryPlan).toMatchInlineSnapshot(`
+      QueryPlan {
+        Sequence {
+          Fetch(service: "books") {
+            {
+              books {
+                __typename
+                isbn
+                title
+                year
+              }
+            }
+          },
+          Flatten(path: "books.@") {
+            Fetch(service: "product") {
+              {
+                ... on Book {
+                  __typename
+                  isbn
+                  title
+                  year
+                }
+              } =>
+              {
+                ... on Book {
+                  name
+                }
+              }
+            },
+          },
+        },
+      }
+    `);
+  });
+
+  it(`interface inside interface should expand into possible types only`, () => {
+    const query = gql`
+      query {
+        product(upc: "") {
+          details {
+            country
+          }
+        }
+      }
+    `;
+
+    const queryPlan = buildQueryPlan(buildOperationContext(schema, query));
+
+    expect(queryPlan).toMatchInlineSnapshot(`
+    QueryPlan {
+      Fetch(service: "product") {
+        {
+          product(upc: "") {
+            __typename
+            ... on Book {
+              details {
+                country
+              }
+            }
+            ... on Furniture {
+              details {
+                country
+              }
+            }
+          }
+        }
+      },
+    }
+    `);
+  });
 });

packages/apollo-gateway/src/buildQueryPlan.ts

@@ -19,6 +19,7 @@ import {
   isListType,
   isNamedType,
   isObjectType,
+  isInterfaceType,
   Kind,
   OperationDefinitionNode,
   SelectionSetNode,
@@ -402,6 +403,17 @@ function splitFields(
       if (isObjectType(parentType)) {
         // If parent type is an object type, we can directly look for the right
         // group.
+
+        // ParentTypes collected from fragments. Multiple values mean nested fragments
+        if (field.parentTypesArray) {
+          let possibleParentTypes = field.parentTypesArray.map(type =>
+            context.getPossibleTypes(type),
+          );
+          if (!possibleParentTypes.every(arr => arr.includes(parentType))) {
+            continue;
+          }
+        }
+
         const group = groupForField(field as Field<GraphQLObjectType>);
         group.fields.push(
           completeField(
@@ -422,7 +434,19 @@ function splitFields(
           GraphQLObjectType
         >();
 
-        for (const runtimeParentType of context.getPossibleTypes(parentType)) {
+        let possibleTypes = context.getPossibleTypes(parentType);
+
+        // ParentTypes collected from fragments. Multiple values mean nested fragments
+        if (field.parentTypesArray) {
+          let possibleParentTypes = field.parentTypesArray.map(type =>
+            context.getPossibleTypes(type),
+          );
+          possibleTypes = possibleTypes.filter(type =>
+            possibleParentTypes.every(arr => arr.includes(type)),
+          );
+        }
+
+        for (const runtimeParentType of possibleTypes) {
           const fieldDef = context.getFieldDef(
             runtimeParentType,
             field.fieldNode,
@@ -464,15 +488,26 @@ function completeField(
   fields: FieldSet,
 ): Field {
   const { fieldNode, fieldDef } = fields[0];
-  const returnType = getNamedType(fieldDef.type);
+
+  let returnType = getNamedType(fieldDef.type);
+
+  if (isObjectType(parentType) || isInterfaceType(parentType)) {
+    // We should find field type by name, because it may be changed after
+    // replacing parent type inside splitFields function.
+    // For union only __typename may be requested and it's type
+    // will be taken from fieldDef
+    const realField = parentType.getFields()[fieldDef.name];
+    if (realField) {
+      returnType = getNamedType(realField.type);
+    }
+  }
 
   if (!isCompositeType(returnType)) {
     // FIXME: We should look at all field nodes to make sure we take directives
     // into account (or remove directives for the time being).
     return { parentType, fieldNode, fieldDef };
   } else {
     // For composite types, we need to recurse.
-
     const fieldPath = addPath(path, getResponseName(fieldNode), fieldDef.type);
 
     const subGroup = new FetchGroup(parentGroup.serviceName);
@@ -516,12 +551,18 @@ function collectFields(
   visitedFragmentNames: { [fragmentName: string]: boolean } = Object.create(
     null,
   ),
+  parentTypesArray: GraphQLCompositeType[] = [],
 ): FieldSet {
   for (const selection of selectionSet.selections) {
     switch (selection.kind) {
       case Kind.FIELD:
         const fieldDef = context.getFieldDef(parentType, selection);
-        fields.push({ parentType, fieldNode: selection, fieldDef });
+        fields.push({
+          parentType,
+          fieldNode: selection,
+          fieldDef,
+          parentTypesArray,
+        });
         break;
       case Kind.INLINE_FRAGMENT:
         collectFields(
@@ -530,6 +571,7 @@ function collectFields(
           selection.selectionSet,
           fields,
           visitedFragmentNames,
+          [...parentTypesArray, parentType],
         );
         break;
       case Kind.FRAGMENT_SPREAD:
@@ -551,6 +593,7 @@ function collectFields(
           fragment.selectionSet,
           fields,
           visitedFragmentNames,
+          [...parentTypesArray, parentType],
         );
         break;
     }