From 27bd3ab4283a6226b55b9c11554d853d112cde4c Mon Sep 17 00:00:00 2001
From: 2881099 <2881099@qq.com>
Date: Mon, 7 Dec 2020 23:52:13 +0800
Subject: [PATCH] update

---
 分组聚合查询.md | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/分组聚合查询.md b/分组聚合查询.md
index 4c57c3d..1a224f0 100644
--- a/分组聚合查询.md
+++ b/分组聚合查询.md
@@ -3,7 +3,8 @@ static IFreeSql fsql = new FreeSql.FreeSqlBuilder()
     .UseConnectionString(FreeSql.DataType.MySql, connectionString)
     .Build(); //请务必定义成 Singleton 单例模式
 
-class Topic {
+class Topic 
+{
     [Column(IsIdentity = true, IsPrimary = true)]
     public int Id { get; set; }
     public int Clicks { get; set; }
@@ -31,6 +32,35 @@ var list = fsql.Select<Topic>()
 
 > 不分组求聚合值，请使用 ToAggregate 替代 ToList
 
+## 导航属性
+
+假如 Topic 有导航属性 Category，Category 又有导航属性 Area，导航属性分组代码如下：
+
+```csharp
+var list = fsql.Select<Topic>()
+    .GroupBy(a => new { a.Clicks, a.Category })
+    .ToList(a => new { a.Key.Category.Area.Name });
+```
+
+如上这样编写，会报错无法解析 a.Key.Category.Area.Name，解决办法使用 Include：
+
+```csharp
+var list = fsql.Select<Topic>()
+    .Include(a => a.Category.Area)
+    //必须添加此行，否则只分组 Category 而不包含它的下级导航属性 Area
+
+    .GroupBy(a => new { a.Clicks, a.Category })
+    .ToList(a => new { a.Key.Category.Area.Name });
+```
+
+但是，你还可以这样解决：
+
+```csharp
+var list = fsql.Select<Topic>()
+    .GroupBy(a => new { a.Clicks, a.Category, a.Category.Area })
+    .ToList(a => new { a.Key.Area.Name });
+```
+
 ## API
 
 | 方法 | 返回值 | 参数 | 描述 |