fix(core): optimize sidebar tag performance (#7633)

packages/frontend/core/src/modules/explorer/views/nodes/tag/index.tsx

@@ -3,6 +3,7 @@ import {
   type DropTargetOptions,
   toast,
 } from '@affine/component';
+import type { Tag } from '@affine/core/modules/tag';
 import { TagService } from '@affine/core/modules/tag';
 import type { AffineDNDData } from '@affine/core/types/dnd';
 import { useI18n } from '@affine/i18n';
@@ -46,7 +47,6 @@ export const ExplorerTagNode = ({
   const tagRecord = useLiveData(tagService.tagList.tagByTagId$(tagId));
   const tagColor = useLiveData(tagRecord?.color$);
   const tagName = useLiveData(tagRecord?.value$);
-  const tagDocIds = useLiveData(tagRecord?.pageIds$);
 
   const Icon = useCallback(
     ({ className }: { className?: string }) => {
@@ -181,16 +181,27 @@ export const ExplorerTagNode = ({
       dropEffect={handleDropEffectOnTag}
       data-testid={`explorer-tag-${tagId}`}
     >
-      {tagDocIds?.map(docId => (
-        <ExplorerDocNode
-          key={docId}
-          docId={docId}
-          reorderable={false}
-          location={{
-            at: 'explorer:tags:docs',
-          }}
-        />
-      ))}
+      <ExplorerTagNodeDocs tag={tagRecord} />
     </ExplorerTreeNode>
   );
 };
+
+/**
+ * the `tag.pageIds$` has a performance issue,
+ * so we split the tag node children into a separate component,
+ * so it won't be rendered when the tag node is collapsed.
+ */
+export const ExplorerTagNodeDocs = ({ tag }: { tag: Tag }) => {
+  const tagDocIds = useLiveData(tag.pageIds$);
+
+  return tagDocIds.map(docId => (
+    <ExplorerDocNode
+      key={docId}
+      docId={docId}
+      reorderable={false}
+      location={{
+        at: 'explorer:tags:docs',
+      }}
+    />
+  ));
+};

packages/frontend/core/src/modules/tag/entities/tag-list.ts

@@ -12,8 +12,18 @@ export class TagList extends Entity {
     super();
   }
 
+  private readonly pool = new Map<string, Tag>();
+
   readonly tags$ = LiveData.from(this.store.watchTagIds(), []).map(ids => {
-    return ids.map(id => this.framework.createEntity(Tag, { id }));
+    return ids.map(id => {
+      const exists = this.pool.get(id);
+      if (exists) {
+        return exists;
+      }
+      const record = this.framework.createEntity(Tag, { id });
+      this.pool.set(id, record);
+      return record;
+    });
   });
 
   createTag(value: string, color: string) {

packages/frontend/core/src/modules/tag/entities/tag.ts

@@ -62,6 +62,10 @@ export class Tag extends Entity<{ id: string }> {
     });
   }
 
+  /**
+   * @deprecated performance issue here, use with caution until it is fixed
+   * @fixme(EYHN): page.meta$ has performance issue
+   */
   readonly pageIds$ = LiveData.computed(get => {
     const pages = get(this.docs.list.docs$);
     return pages