Question

我的Linq查询需要额外的where子句。例如，如果客户选择日期过滤器，所以我需要过滤到我的查询等...当我尝试myQuery.Where谓词时，只有group by的字段可见。

如何在查询中附加新的where条件。

//for example i need dynamically append o.OrderDate==Datetime.Now or another where clause

var myQuery =(from o in _db.Orders
join l in _db.OrderLines.Where(x => x.ParaBirimi == model.ParaBirimi) on o.orderId equals
    l.OrderId
where o.OrderDate.Value.Year == year1 
group o by new {o.OrderDate.Value.Month}
into g
select
    new
    {
        Month = g.Key.Month,
        Total = g.Select(t => t.OrderLines.Sum(s => s.OrderTotal)).FirstOrDefault()
    });

Answer 1

在查询结束时你为时已晚，无法添加新的Where。您已经对数据进行了分组并对其进行了投影，几乎删除了所有字段。

尝试：

var baseQuery = from o in _db.Orders
                join l in _db.OrderLines.Where(x => x.ParaBirimi == model.ParaBirimi) on o.orderId equals l.OrderId
                where o.OrderDate.Value.Year == year1
                select new { Order = o, OrderLine = l };

if (something)
{
     baseQuery = baseQuery.Where(x => x.Order.Foo == "Bar");
}

var myQuery = (from o in baseQuery
               group o by new { o.Order.OrderDate.Value.Month }
                   into g
                   select
                       new
                       {
                           Month = g.Key.Month,
                           Total = g.Sum(t => t.OrderLine.OrderTotal)
                       });

显然，您可以拥有多个if。每个.Where()都在&&（AND）与其他条件。

请注意join的结果是如何在具有两个属性的匿名类中投影的：Order和OrderLine

带组的Linq动态查询

1 个答案: