.net - Entity Framework (QueryBuilder) - where 子句 "it"前缀

Question

我最近遇到了以下 Entity Framework 的语法。注意 where 子句 -

.Where("it.LastName = @ln AND it.FirstName = @fn")

什么 it.做？为什么 it而不是 Contacts.LastName？任何详细信息都会有所帮助。提前致谢。

string firstName = @"Frances";
string lastName = @"Adams";

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    // Get the contacts with the specified name.
    ObjectQuery<Contact> contactQuery = context.Contacts
        .Where("it.LastName = @ln AND it.FirstName = @fn",
        new ObjectParameter("ln", lastName),
        new ObjectParameter("fn", firstName));

    // Iterate through the collection of Contact items.
    foreach (Contact result in contactQuery)
        Console.WriteLine("Last Name: {0}; First Name: {1}",
        result.LastName, result.FirstName);
}

Answer 1

基于 this article , "it"将 ObjectQuery 称为引用参数的默认名称。通过使用 ObjectQuery 的 Name 属性，您实际上可以更改它，以便在您的 where 子句中可以将其引用为您希望的任何名称:

ObjectQuery<Contact> contactQuery;
contactQuery.Name = "contact";
contactQuery = context.Contacts
  .Where("contact.LastName = @ln AND contact.FirstName = @fn",
   new ObjectParameter("ln", lastName),
   new ObjectParameter("fn", firstName));  

可能不完全像上面显示的那样，但它给出了一般的想法。