Feature/custom resolve field

src/execution/__tests__/resolve-test.js

@@ -126,4 +126,38 @@ describe('Execute: resolve function', () => {
       },
     });
   });
+
+  it('context value custom resolve field is called', () => {
+    const rootValue = {
+      test() {
+        return 'default';
+      },
+    };
+
+    const result = executeSync({
+      schema: testSchema({ type: GraphQLString }),
+      document: parse('{ test }'),
+      rootValue,
+      contextValue: {
+        customResolveField: () => 'custom',
+      },
+    });
+    expect(result).to.deep.equal({
+      data: {
+        test: 'custom',
+      },
+    });
+
+    const defaultResult = executeSync({
+      schema: testSchema({ type: GraphQLString }),
+      document: parse('{ test }'),
+      rootValue,
+      contextValue: {},
+    });
+    expect(defaultResult).to.deep.equal({
+      data: {
+        test: 'default',
+      },
+    });
+  });
 });

src/execution/execute.d.ts

@@ -193,3 +193,11 @@ export function getFieldDef(
   parentType: GraphQLObjectType,
   fieldName: string,
 ): Maybe<GraphQLField<any, any>>;
+
+export function resolveField(
+  exeContext: ExecutionContext,
+  parentType: GraphQLObjectType,
+  source: any,
+  fieldNodes: Array<FieldNode>,
+  path: Path,
+): Promise<any> | any;

src/execution/execute.js

@@ -461,13 +461,32 @@ function executeFields(
   for (const responseName of Object.keys(fields)) {
     const fieldNodes = fields[responseName];
     const fieldPath = addPath(path, responseName, parentType.name);
-    const result = resolveField(
-      exeContext,
-      parentType,
-      sourceValue,
-      fieldNodes,
-      fieldPath,
-    );
+
+    let result;
+
+    // If a custom resolve field function is provided by the execution context, use it
+    // This allows for more application specific resolve logic such as caching by specific
+    // document types and execution context values
+    const contextValue = exeContext && (exeContext.contextValue: any);
+    if (typeof contextValue?.customResolveField === 'function') {
+      result = contextValue.customResolveField(
+        exeContext,
+        parentType,
+        sourceValue,
+        fieldNodes,
+        fieldPath,
+      );
+    }
+    // otherwise fall back on resolveField
+    else {
+      result = resolveField(
+        exeContext,
+        parentType,
+        sourceValue,
+        fieldNodes,
+        fieldPath,
+      );
+    }
 
     if (result !== undefined) {
       results[responseName] = result;
@@ -627,7 +646,7 @@ function getFieldEntryKey(node: FieldNode): string {
  * then calls completeValue to complete promises, serialize scalars, or execute
  * the sub-selection-set for objects.
  */
-function resolveField(
+export function resolveField(
   exeContext: ExecutionContext,
   parentType: GraphQLObjectType,
   source: mixed,