entity-framework - 单个查询中的EF多个聚合

Question

我想根据不同的条件获取一组计数:

 var invoices = new AccountingEntities().Transactions
 var c1 = invoices.Count(i=>i.Type = 0);
 var c2 = invoices.Count(i=>i.Type = 1);
 var c3 = invoices.Count(i=>i.Type = 2);

如何在一次数据库往返中调用所有三个查询以提高性能？

Answer 1

当然，只需将您的三个计数包含在 POCO 或匿名类型中:

using (var invoices = new AccountingEntities())
{
    var c = (from i in invoices.Transactions
             select new 
             {
                 c1 = invoices.Count(i=>i.Type = 0),
                 c2 = invoices.Count(i=>i.Type = 1),
                 c3 = invoices.Count(i=>i.Type = 2)
             }).Single();           
}

另外，正如我展示的那样，处理您的上下文。