From fcb885b5f4c34d01510b00356031d1e2b25ec042 Mon Sep 17 00:00:00 2001
From: Markus Padourek <markus.padourek@gmail.com>
Date: Thu, 13 Oct 2016 16:36:14 +0100
Subject: [PATCH] Support returning of promise-like objects.

---
 graphql/execution/executor.py           |  8 ++--
 graphql/execution/tests/test_resolve.py | 57 +++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/graphql/execution/executor.py b/graphql/execution/executor.py
index 2cfd65e9..015b8a76 100644
--- a/graphql/execution/executor.py
+++ b/graphql/execution/executor.py
@@ -3,7 +3,7 @@
 import logging
 import sys
 
-from promise import Promise, promise_for_dict, promisify
+from promise import Promise, promise_for_dict, promisify, is_thenable
 
 from ..error import GraphQLError, GraphQLLocatedError
 from ..pyutils.default_ordered_dict import DefaultOrderedDict
@@ -100,7 +100,7 @@ def execute_field_callback(results, response_name):
         if result is Undefined:
             return results
 
-        if is_promise(result):
+        if is_thenable(result):
             def collect_result(resolved_result):
                 results[response_name] = resolved_result
                 return results
@@ -206,7 +206,7 @@ def complete_value_catching_error(exe_context, return_type, field_asts, info, re
     # resolving a null value for this field if one is encountered.
     try:
         completed = complete_value(exe_context, return_type, field_asts, info, result)
-        if is_promise(completed):
+        if is_thenable(completed):
             def handle_error(error):
                 exe_context.errors.append(error)
                 return Promise.fulfilled(None)
@@ -240,7 +240,7 @@ def complete_value(exe_context, return_type, field_asts, info, result):
     """
     # If field type is NonNull, complete for inner type, and throw field error if result is null.
 
-    if is_promise(result):
+    if is_thenable(result):
         return promisify(result).then(
             lambda resolved: complete_value(
                 exe_context,
diff --git a/graphql/execution/tests/test_resolve.py b/graphql/execution/tests/test_resolve.py
index 05851f0a..42b96899 100644
--- a/graphql/execution/tests/test_resolve.py
+++ b/graphql/execution/tests/test_resolve.py
@@ -6,6 +6,35 @@
                           GraphQLInputObjectField, GraphQLInputObjectType,
                           GraphQLInt, GraphQLList, GraphQLNonNull,
                           GraphQLObjectType, GraphQLSchema, GraphQLString)
+from promise import Promise
+
+class CustomPromise(object):
+    def __init__(self, fn=None, promise=None):
+        self._promise = promise or Promise(fn)
+
+    def get(self, _=None):
+        raise NotImplementedError("Blocking for results not allowed. Use 'then' if you want to "
+                                  "work with the result.")
+
+    def then(self, success=None, failure=None):
+        return self.__class__(promise=self._promise.then(success, failure))
+
+    def __getattr__(self, item):
+        return getattr(self._promise, item)
+
+    @classmethod
+    def fulfilled(cls, x):
+        p = cls()
+        p.fulfill(x)
+        return p
+
+    resolve = fulfilled
+
+    @classmethod
+    def rejected(cls, reason):
+        p = cls()
+        p.reject(reason)
+        return p
 
 
 def _test_schema(test_field):
@@ -73,6 +102,34 @@ def resolver(source, args, *_):
     ]
 
 
+def test_handles_resolved_promises():
+    def resolver(source, args, *_):
+        return Promise.resolve('foo')
+
+    schema = _test_schema(GraphQLField(
+        GraphQLString,
+        resolver=resolver
+    ))
+
+    result = graphql(schema, '{ test }', None)
+    assert not result.errors
+    assert result.data == {'test': 'foo'}
+
+
+def test_handles_resolved_custom_promises():
+    def resolver(source, args, *_):
+        return CustomPromise.resolve('custom_foo')
+
+    schema = _test_schema(GraphQLField(
+        GraphQLString,
+        resolver=resolver
+    ))
+
+    result = graphql(schema, '{ test }', None)
+    assert not result.errors
+    assert result.data == {'test': 'custom_foo'}
+
+
 def test_maps_argument_out_names_well():
     def resolver(source, args, *_):
         return json.dumps([source, args], separators=(',', ':'))