fix: gitee pr 78

docs/uniCloud/cf-database.md

@@ -3393,8 +3393,8 @@ let res = await db.collection('orders').aggregate()
 如需orders关联books，book再关联authors查询，可以在pipeline内再使用lookup
 
 ```js
-const dbCmd = db.command;
 const db = cloud.database()
+const dbCmd = db.command
 const $ = db.command.aggregate
 let res = await db.collection('orders').aggregate()
   .lookup({
@@ -3404,7 +3404,7 @@ let res = await db.collection('orders').aggregate()
     },
     pipeline: $.pipeline()
       .match(
-        dbCmd .expr($.eq(['$_id', '$$book_id']))
+        dbCmd.expr($.eq(['$_id', '$$book_id']))
       )
       .lookup({
         from: 'authors',
@@ -3413,7 +3413,7 @@ let res = await db.collection('orders').aggregate()
         },
         pipeline: $.pipeline()
           .match(
-            dbCmd .expr($.eq(['$_id', '$$author_id']))
+            dbCmd.expr($.eq(['$_id', '$$author_id']))
           )
           .done(),
         as: 'authorList'