c# - 按 Entity Framework 中的子表排序

Question

在我的 Linq 中，我访问了一个简单的主/详细表:

_db.Countries.Include(x=>x.People);

我希望人们按姓氏排序，但是当我在包含中包含顺序时，它会出错:

The Include path expression must refer to a navigation property defined on the type. 
Use dotted paths for reference navigation properties and the Select operator for collection navigation properties. Parameter name: path

Answer 1

你可以做到这一点。

var countries = _db.Countries
   .Select(c => new 
   {
       Country = c,
       People = c.People.OrderBy(p => p.Lastname)
   })
   .AsEnumerable() // not execute yet
   .Select(a => a.Country)
   .ToArray(); // execute

即使Select 只选择了国家，匿名类型的People 将连接到每个国家的People 属性。

生成的 sql 将包含 order by query 之类的。

ORDER BY [Project1].[Id] ASC, [Project1].[C1] ASC, [Project1].[Lastname] ASC

附言

作为预先加载的解决方法，您可以做的是修复关系。使用这种方法将只有一次数据库往返，而不是先加载所有国家然后再加载每个人。

Relationship Fix-up is the process by which the EF, links related Entities together. For example fix-up will set the "Customer" property of an Order when a known to be related Customer is materialized from the database. Once you understand fix-up you can leverage it to do all sorts of interesting things. - Entity Framework Jargon by Alex D James