使用 Concat 合并多个 IQueryable 查询 (Entity Framework)

Question

我还是不太清楚，我有两个问题，例如：

IQueryable<Ad> list1 = db.Ads.Where(x => x.IsModerated == true);
IQueryable<Ad> list2 = db.Ads.Where(x => x.TypeId == 1);
IQueryable<Ad> list = list1.Concat(list2);

foreach(var item in list)
{
   ...
}

是一两次数据库调用吗？

Answer 1

它只执行一次。这是延迟执行的示例，阅读此 blog 了解更多详细信息

IQueryable<Ad> list1 = db.Ads.Where(x => x.IsModerated == true); -- builds query 1, no db execution
IQueryable<Ad> list2 = db.Ads.Where(x => x.TypeId == 1); -- builds query 2, no db execution
IQueryable<Ad> list = list1.Concat(list2); -- -- builds combine query 'UNION ALL', no db execution

foreach(var item in list) -- query executes here
{
   ...
}

使用 Concat 合并多个 IQueryable 查询 (Entity Framework)

Merging multiple IQueryable queries using Concat (Entity Framework)

c#

entity-framework

iqueryable