Detect format from output file path (#868)

* Detect format from output file path

* Fix tests

* Add test for exporting graphql file

* Add some documentation

docs/introspection.rst

@@ -29,6 +29,20 @@ you're ready to use Relay with Graphene GraphQL implementation.
 
 The schema file is sorted to create a reproducible canonical representation.
 
+GraphQL SDL Representation
+--------------------------
+
+The schema can also be exported as a GraphQL SDL file by changing the file
+extension :
+
+.. code:: bash
+
+    ./manage.py graphql_schema --schema tutorial.quickstart.schema --out schema.graphql
+
+When exporting the schema as a ``.graphql`` file the ``--indent`` option is
+ignored.
+
+
 Advanced Usage
 --------------
 

graphene_django/management/commands/graphql_schema.py

@@ -1,3 +1,4 @@
+import os
 import importlib
 import json
 import functools
@@ -5,6 +6,7 @@ import functools
 from django.core.management.base import BaseCommand, CommandError
 from django.utils import autoreload
 
+from graphql import print_schema
 from graphene_django.settings import graphene_settings
 
 
@@ -44,24 +46,40 @@ class CommandArguments(BaseCommand):
 
 
 class Command(CommandArguments):
-    help = "Dump Graphene schema JSON to file"
+    help = "Dump Graphene schema as a JSON or GraphQL file"
     can_import_settings = True
 
-    def save_file(self, out, schema_dict, indent):
+    def save_json_file(self, out, schema_dict, indent):
         with open(out, "w") as outfile:
             json.dump(schema_dict, outfile, indent=indent, sort_keys=True)
 
+    def save_graphql_file(self, out, schema):
+        with open(out, "w") as outfile:
+            outfile.write(print_schema(schema))
+
     def get_schema(self, schema, out, indent):
         schema_dict = {"data": schema.introspect()}
         if out == "-":
             self.stdout.write(json.dumps(schema_dict, indent=indent, sort_keys=True))
         else:
-            self.save_file(out, schema_dict, indent)
+            # Determine format
+            _, file_extension = os.path.splitext(out)
+
+            if file_extension == ".graphql":
+                self.save_graphql_file(out, schema)
+            elif file_extension == ".json":
+                self.save_json_file(out, schema_dict, indent)
+            else:
+                raise CommandError(
+                    'Unrecognised file format "{}"'.format(file_extension)
+                )
 
             style = getattr(self, "style", None)
             success = getattr(style, "SUCCESS", lambda x: x)
 
-            self.stdout.write(success("Successfully dumped GraphQL schema to %s" % out))
+            self.stdout.write(
+                success("Successfully dumped GraphQL schema to {}".format(out))
+            )
 
     def handle(self, *args, **options):
         options_schema = options.get("schema")

graphene_django/tests/test_command.py

@@ -1,17 +1,21 @@
+from textwrap import dedent
+
 from django.core import management
-from mock import patch, mock_open
+from mock import mock_open, patch
 from six import StringIO
 
+from graphene import ObjectType, Schema, String
 
-@patch("graphene_django.management.commands.graphql_schema.Command.save_file")
+
-def test_generate_file_on_call_graphql_schema(savefile_mock, settings):
+@patch("graphene_django.management.commands.graphql_schema.Command.save_json_file")
+def test_generate_json_file_on_call_graphql_schema(savefile_mock, settings):
     out = StringIO()
     management.call_command("graphql_schema", schema="", stdout=out)
     assert "Successfully dumped GraphQL schema to schema.json" in out.getvalue()
 
 
 @patch("json.dump")
-def test_files_are_canonical(dump_mock):
+def test_json_files_are_canonical(dump_mock):
     open_mock = mock_open()
     with patch("graphene_django.management.commands.graphql_schema.open", open_mock):
         management.call_command("graphql_schema", schema="")
@@ -25,3 +29,34 @@ def test_files_are_canonical(dump_mock):
     assert (
         dump_mock.call_args[1]["indent"] > 0
     ), "output should be pretty-printed by default"
+
+
+def test_generate_graphql_file_on_call_graphql_schema():
+    class Query(ObjectType):
+        hi = String()
+
+    mock_schema = Schema(query=Query)
+
+    open_mock = mock_open()
+    with patch("graphene_django.management.commands.graphql_schema.open", open_mock):
+        management.call_command(
+            "graphql_schema", schema=mock_schema, out="schema.graphql"
+        )
+
+    open_mock.assert_called_once()
+
+    handle = open_mock()
+    assert handle.write.called_once()
+
+    schema_output = handle.write.call_args[0][0]
+    assert schema_output == dedent(
+        """\
+        schema {
+          query: Query
+        }
+
+        type Query {
+          hi: String
+        }
+    """
+    )