Place unknown artists last when sorting by artist

backend/src/index.ts

@@ -201,10 +201,10 @@ const resolvers = {
           sortOrder = { titleSort: -1, id: 1 };
           break;
         case "ARTIST_ASC":
-          sortOrder = { artist_display: 1, id: 1 };
+          sortOrder = { artistUnknown: 1, artist_display: 1, id: 1 };
           break;
         case "ARTIST_DESC":
-          sortOrder = { artist_display: -1, id: 1 };
+          sortOrder = { artistUnknown: 1, artist_display: -1, id: 1 };
           break;
         default:
           sortOrder = { id: 1 };
@@ -217,6 +217,24 @@ const resolvers = {
               { $match: filter },
               {
                 $set: {
+                  artistUnknown: {
+                    $cond: [
+                      {
+                        $in: [
+                          {
+                            $toLower: {
+                              $trim: {
+                                input: { $ifNull: ["$artist_display", ""] },
+                              },
+                            },
+                          },
+                          ["", "unknown"],
+                        ],
+                      },
+                      1,
+                      0,
+                    ],
+                  },
                   titleSort: {
                     $reduce: {
                       input: ['"', "“", "”"],
@@ -235,7 +253,7 @@ const resolvers = {
               { $sort: sortOrder },
               { $skip: offset },
               { $limit: limit },
-              { $unset: "titleSort" },
+              { $unset: ["titleSort", "artistUnknown"] },
             ],
             {
               collation: { locale: "en", strength: 1 },

backend/tests/artworks-sorting.test.ts

@@ -64,6 +64,12 @@ async function fetchArtworks(
   return result.data.artworks;
 }
 
+function isUnknownArtist(artist: string | null | undefined): boolean {
+  const name = artist?.trim().toLowerCase() ?? "";
+
+  return name === "" || name === "unknown";
+}
+
 describe("Artwork sorting API", () => {
   it("sorts by ascending ID when no sorting option is provided", async () => {
     const result = await fetchArtworks();
@@ -178,6 +184,7 @@ describe("Artwork sorting API", () => {
       },
     ]);
   });
+
   it("ignores curly double quotes when sorting titles", async () => {
     const result = await fetchArtworks("TITLE_ASC", 100, 0, "painting");
 
@@ -198,4 +205,39 @@ describe("Artwork sorting API", () => {
       "“Bamboo” section, from the Mustard Seed Garden Manual of Painting",
     );
   });
+
+  it.each<ArtworkSort>(["ARTIST_ASC", "ARTIST_DESC"])(
+    "places unknown artists last across pages with %s",
+    async (sort) => {
+      const pageSize = 100;
+      const firstPage = await fetchArtworks(sort, pageSize, 0);
+      const artworks = [...firstPage.artworks];
+
+      for (
+        let offset = pageSize;
+        offset < firstPage.totalCount;
+        offset += pageSize
+      ) {
+        const page = await fetchArtworks(sort, pageSize, offset);
+
+        expect(page.totalCount).toBe(firstPage.totalCount);
+        artworks.push(...page.artworks);
+      }
+
+      expect(artworks).toHaveLength(firstPage.totalCount);
+
+      const firstUnknownIndex = artworks.findIndex((artwork) =>
+        isUnknownArtist(artwork.artist_display),
+      );
+
+      expect(firstUnknownIndex).toBeGreaterThan(0);
+
+      for (const artwork of artworks.slice(firstUnknownIndex)) {
+        expect(isUnknownArtist(artwork.artist_display)).toBe(true);
+      }
+
+      const ids = artworks.map((artwork) => artwork.id);
+      expect(new Set(ids).size).toBe(artworks.length);
+    },
+  );
 });