使用 EntityFramework LINQ 查询的具有表计数的 SQL 联合

Question

我正在尝试使用 LINQ 和实体框架复制下面的 SQL，但无法弄清楚应该如何编写。

我的简单 LINQ 版本对每个表进行查询

public IActionResult Index()
{
      dynamic view = new ExpandoObject();

      view.AppUsers             = Context.AppUsers.Count();
      view.CustomerShops        = Context.CustomerShops.Count();
      view.FavouriteOrders      = Context.FavouriteOrders.Count();
      view.Items                = Context.Items.Count();
      view.ItemVariations       = Context.ItemVariations.Count();
      view.MenuCategories       = Context.MenuCategories.Count();
      view.MenuCategoryProducts = Context.MenuCategoryProducts.Count();
      view.Orders               = Context.Orders.Count();
      view.Products             = Context.Products.Count();
      view.ProductVariations    = Context.ProductVariations.Count();
      view.Shops                = Context.Shops.Count();
      view.Staffs               = Context.Staffs.Count();

      return View(view);
}

我不时使用这种模式来报告我的列数，并认为这在 LINQ 中应该很容易做到，但到目前为止还没有运气。

这种纯 SQL UNION 只会生成 1 个 SQL 请求，而不是每个表一个请求。

select * from (
  select 'asp_net_roles' as type, count(*) from asp_net_roles
  union
  select 'asp_net_user_roles' as type, count(*) from asp_net_user_roles
  union
  select 'asp_net_users' as type, count(*) from asp_net_users
  union
  select 'app_users' as type, count(*) from app_users
  union
  select 'shops' as type, count(*) from shops
  union
  select 'staffs' as type, count(*) from shops
  union
  select 'items' as type, count(*) from items
  union
  select 'item_variations' as type, count(*) from item_variations
  union
  select 'products' as type, count(*) from products
  union
  select 'product_variations' as type, count(*) from product_variations
  union
  select 'menu_categories' as type, count(*) from menu_categories
) as counters
order by 1;

我看到了部分实现 [linq-group-by-multiple-tables] (https://stackoverflow.com/a/3435503/473923)，但这是基于分组数据。

仅供参考：我是 C#/Linq 新手，如果这个接缝很明显，我很抱歉。

Answer 1

使用this code from my answer

然后用结果填充ExpandoObject：

var tablesinfo = Context.GetTablesInfo();
var expando = new ExpandoObject();
if (tablesinfo != null)
{
   var dic = (IDictionary<string, object>)expando;
   foreach(var info in tablesinfo)
   {
       dic.Add(info.TableName, info.RecordCount);
   }
}

想法是，如果您按常量对实体进行分组，则可以进行 UNION 计数。 示意函数构建以下 IQueryable 表达式：

var tablesinfo =
   Context.AppUsers.GroupBy(x => 1).Select(g => new TableInfo{ TableName = "asp_net_roles", RecordCount = g.Count() })
   .Concat(Context.MenuCategories.GroupBy(x => 1).Select(g => new TableInfo{ TableName = "menu_categories", RecordCount = g.Count() }))
   .Concat(Context.Items.GroupBy(x => 1).Select(g => new TableInfo{ TableName = "items", RecordCount = g.Count() }))
   ....

Answer 2

您的 LINQ 查询没有问题。这是非常可接受的方法。然而这并不是最有效的。

无需从单个表中一一获取计数。您可以使用系统表Sys.Objects 和Sys.Partitions 一次从所有表中获取计数。只需尝试在您的数据库中运行此查询。

SELECT A.Name AS TableName, SUM(B.rows) AS RecordCount  
FROM sys.objects A INNER JOIN sys.partitions B 
ON A.object_id = B.object_id  
WHERE A.type = 'U' AND B.index_id IN (0, 1)
GROUP BY A.Name

为了快速响应和更简洁的代码，您可以将此 SQL 查询存储在字符串变量中，然后运行 ​​LINQ

var result = dataContext.ExecuteQuery<YOUR_MODEL_CLASS>
             (your_string_query);

Answer 3

我会这样写：

Dictionary<string, int> view = new() {
   new() {'asp_net_roles', Context.AppUsers.Count() },
   ...
}
return View(view);

也许不是最纯粹的方式，但可以完成工作（除非我误解了你试图完成的工作）