Integrate async data loaders for box product, size, and tags

- create loaders and run async query execution when dispatching GraphQL
  request
- obtain loaders from GraphQL context in resolvers
- split product resolver due to different authz enforcement
cf.
graphql-python/graphql-server#66
https://lightrun.com/answers/graphql-python-graphene-consider-supporting-promise-based-dataloaders-in-v3
graphql-python/graphql-core#71

back/boxtribute_server/graph_ql/resolvers.py

@@ -219,26 +219,33 @@ def resolve_qr_code(obj, _, qr_code=None):
 
 
 @box.field("tags")
-def resolve_box_tags(box_obj, _):
-    return (
-        Tag.select()
-        .join(TagsRelation)
-        .where(
-            (TagsRelation.object_id == box_obj.id)
-            & (TagsRelation.object_type == TaggableObjectType.Box)
-        )
-    )
+def resolve_box_tags(box_obj, info):
+    return info.context["tags_for_box_loader"].load(box_obj.id)
 
 
 @query.field("product")
+def resolve_product(obj, _, id):
+    product = Product.get_by_id(id)
+    authorize(permission="product:read", base_id=product.base_id)
+    return product
+
+
 @box.field("product")
 @unboxed_items_collection.field("product")
-def resolve_product(obj, _, id=None):
-    product = obj.product if id is None else Product.get_by_id(id)
-    authorize(permission="product:read", base_id=product.base_id)
+def resolve_box_product(obj, info):
+    product = info.context["product_loader"].load(obj.product_id)
+    # Base-specific authz can be omitted here since it was enforced in the box
+    # parent-resolver. It's not possible that the box's product is assigned to a
+    # different base than the box is in
+    authorize(permission="product:read")
     return product
 
 
+@box.field("size")
+def resolve_size(box_obj, info):
+    return info.context["size_loader"].load(box_obj.size_id)
+
+
 @query.field("box")
 @convert_kwargs_to_snake_case
 def resolve_box(*_, label_identifier):

back/boxtribute_server/loaders.py

@@ -0,0 +1,36 @@
+from collections import defaultdict
+
+from aiodataloader import DataLoader
+
+from .enums import TaggableObjectType
+from .models.definitions.product import Product
+from .models.definitions.size import Size
+from .models.definitions.tag import Tag
+from .models.definitions.tags_relation import TagsRelation
+
+
+class ProductLoader(DataLoader):
+    async def batch_load_fn(self, keys):
+        products = {p.id: p for p in Product.select().where(Product.id << keys)}
+        return [products.get(i) for i in keys]
+
+
+class SizeLoader(DataLoader):
+    async def batch_load_fn(self, keys):
+        sizes = {s.id: s for s in Size.select()}
+        return [sizes.get(i) for i in keys]
+
+
+class TagsForBoxLoader(DataLoader):
+    async def batch_load_fn(self, keys):
+        tags = defaultdict(list)
+        # maybe need different join type
+        for relation in (
+            TagsRelation.select()
+            .join(Tag)
+            .where(TagsRelation.object_type == TaggableObjectType.Box)
+        ):
+            tags[relation.object_id].append(relation.tag)
+
+        # keys are in fact box IDs. Return empty list if box has no tags assigned
+        return [tags.get(i, []) for i in keys]

back/boxtribute_server/routes.py

@@ -1,14 +1,16 @@
 """Construction of routes for web app and API"""
+import asyncio
 import os
 
-from ariadne import graphql_sync
+from ariadne import graphql, graphql_sync
 from ariadne.constants import PLAYGROUND_HTML
 from flask import Blueprint, current_app, jsonify, request
 from flask_cors import cross_origin
 
 from .auth import request_jwt, requires_auth
 from .exceptions import AuthenticationFailed, format_database_errors
 from .graph_ql.schema import full_api_schema, query_api_schema
+from .loaders import ProductLoader, SizeLoader, TagsForBoxLoader
 
 # Blueprint for query-only API. Deployed on the 'api*' subdomains
 api_bp = Blueprint("api_bp", __name__)
@@ -82,15 +84,27 @@ def graphql_playgroud():
 @cross_origin(origin="localhost", headers=["Content-Type", "Authorization"])
 @requires_auth
 def graphql_server():
-    # Note: Passing the request to the context is optional.
-    # In Flask, the current request is always accessible as flask.request
-    success, result = graphql_sync(
-        full_api_schema,
-        data=request.get_json(),
-        context_value=request,
-        debug=current_app.debug,
-        introspection=current_app.debug,
-        error_formatter=format_database_errors,
+    # Start async event loop, required for DataLoader construction, cf.
+    # https://github.com/graphql-python/graphql-core/issues/71#issuecomment-620106364
+    loop = asyncio.new_event_loop()
+    asyncio.set_event_loop(loop)
+
+    # Create DataLoaders and persist them for the time of processing the request
+    context = {
+        "product_loader": ProductLoader(),
+        "size_loader": SizeLoader(),
+        "tags_for_box_loader": TagsForBoxLoader(),
+    }
+
+    success, result = loop.run_until_complete(
+        graphql(
+            full_api_schema,
+            data=request.get_json(),
+            context_value=context,
+            debug=current_app.debug,
+            introspection=current_app.debug,
+            error_formatter=format_database_errors,
+        )
     )
 
     status_code = 200 if success else 400

back/requirements.txt

@@ -8,4 +8,5 @@ peewee-moves==2.1.0
 python-dateutil==2.8.2
 python-dotenv==0.20.0
 python-jose==3.3.0
+aiodataloader==0.2.1
 gunicorn

back/scripts/load-test.js

@@ -34,8 +34,8 @@ const payload = JSON.stringify({
   // query: "query { beneficiaries { elements { firstName } } }",
 
   // C) All boxes for base
-  // query: "query { base(id: 1) { locations { name boxes { totalCount elements { labelIdentifier state size { id label } product { gender name } tags { name id } items } } } } }",
-  query: "query { location(id: 1) { boxes { elements { product { gender name } } } } }",
+  query: "query { base(id: 1) { locations { name boxes { totalCount elements { labelIdentifier state size { id label } product { gender name } tags { name id } numberOfItems } } } } }",
+  // query: "query { location(id: 1) { boxes { elements { product { gender name } } } } }",
 });
 
 export const options = {

back/test/endpoint_tests/test_permissions.py

@@ -223,7 +223,7 @@ def test_invalid_permission_for_shipment_base(read_only_client, mocker, field):
     assert_forbidden_request(read_only_client, query, value={field: None})
 
 
-@pytest.mark.parametrize("field", ["place", "product", "qrCode"])
+@pytest.mark.parametrize("field", ["place", "qrCode"])
 def test_invalid_permission_for_box_field(read_only_client, mocker, default_box, field):
     # verify missing field:read permission
     mocker.patch("jose.jwt.decode").return_value = create_jwt_payload(