smarter cache lookups for "do we own/want this?"

src/app/ItemPage.js

@@ -198,8 +198,8 @@ function ItemPageOwnWantButtons({ itemId }) {
     {
       variables: { itemId },
       onCompleted: (data) => {
-        setCurrentUserOwnsThis(data.item.currentUserOwnsThis);
-        setCurrentUserWantsThis(data.item.currentUserWantsThis);
+        setCurrentUserOwnsThis(data?.item?.currentUserOwnsThis || false);
+        setCurrentUserWantsThis(data?.item?.currentUserWantsThis || false);
       },
     }
   );
@@ -208,6 +208,7 @@ function ItemPageOwnWantButtons({ itemId }) {
     return <Box color="red.400">{error.message}</Box>;
   }
 
+  // TODO: Focus state!
   return (
     <Box display="flex">
       <Skeleton isLoaded={!loading} marginRight="4">
@@ -215,7 +216,7 @@ function ItemPageOwnWantButtons({ itemId }) {
           <VisuallyHidden
             as="input"
             type="checkbox"
-            isChecked={currentUserOwnsThis}
+            checked={currentUserOwnsThis}
             onChange={(e) => {
               setCurrentUserOwnsThis(e.target.checked);
               toast({

src/app/apolloClient.js

@@ -78,6 +78,53 @@ const typePolicies = {
           return undefined;
         }
       },
+
+      currentUserOwnsThis: (cachedValue, { readField }) => {
+        if (cachedValue != null) {
+          return cachedValue;
+        }
+
+        // Do we know what items this user owns? If so, scan for this item.
+        const currentUserRef = readField("currentUser", {
+          __ref: "ROOT_QUERY",
+        });
+        if (!currentUserRef) {
+          return undefined;
+        }
+        const thisItemId = readField("id");
+        const itemsTheyOwn = readField("itemsTheyOwn", currentUserRef);
+        if (!itemsTheyOwn) {
+          return undefined;
+        }
+
+        const theyOwnThisItem = itemsTheyOwn.some(
+          (itemRef) => readField("id", itemRef) === thisItemId
+        );
+        return theyOwnThisItem;
+      },
+      currentUserWantsThis: (cachedValue, { readField }) => {
+        if (cachedValue != null) {
+          return cachedValue;
+        }
+
+        // Do we know what items this user owns? If so, scan for this item.
+        const currentUserRef = readField("currentUser", {
+          __ref: "ROOT_QUERY",
+        });
+        if (!currentUserRef) {
+          return undefined;
+        }
+        const thisItemId = readField("id");
+        const itemsTheyWant = readField("itemsTheyWant", currentUserRef);
+        if (!itemsTheyWant) {
+          return undefined;
+        }
+
+        const theyWantThisItem = itemsTheyWant.some(
+          (itemRef) => readField("id", itemRef) === thisItemId
+        );
+        return theyWantThisItem;
+      },
     },
   },
 };