Question

我正在尝试根据下面的SQL编写Linq to Entities Query

基本上我希望得到最后5个订单的清单，订单日期在（TitleDetails）的子详细信息表中

SELECT t.Name, t.LimpIsbn, t.CasedIsbn, max(td.OrderDate) LastOrder
FROM [inform].[dbo].[Titles] t
left join [inform].[dbo].[TitleDetails] td on t.id = td.TitleId
where td.OrderDate is not null
group by  t.Name, t.LimpIsbn, t.CasedIsbn
order by  max(td.OrderDate) desc

我的代码如下

var query = Context.Titles
            .Include(x => x.MisAccount)
            .Include(x => x.TitleDetails)
            .Where(x => x.TitleDetails.Any());

if (!string.IsNullOrEmpty(model.MisCustomer))
{
    query = query.Where(x => x.MisAccount.Code == model.MisCustomer);
}

if (!User.IsInRole(Permission.CanAccessAllCustomers.ToString()))
{
    var predicate = PredicateBuilder.False<Title>();

     foreach (var customer in validCustomers)
     {
         var cust = customer.Code;
         predicate = predicate.Or(x => x.MisAccount.Code == cust);
     }

    query = query.AsExpandable().Where(predicate);
}

model.LatestOrders = query.Take(5)

在视图中可以枚举LatestOrders。

我已经查看了有关Linq Group的各种其他来源，这些来源与单表分组有关，我正努力将其转换为多表。

Answer 1

几乎就是那样

var last5Item = from td in Context.TitleDetails.OrderByDescending(i => i.OrderDate).Take(5)
                join t in Context.Titles on td.TitleId equals t.id
                select ..

Answer 2

您的SQL查询可以转换为此linq查询：

var query =(from t in Context.Titles
            join td in Context.TitleDetails on t.id equals td.TitleId into tds
            from e in tds.DefaultIfEmpty()
            where e.OrderDate!=null
            group  e.OrderDate by new {t.Name, t.LimpIsbn, t.CasedIsbn} into groups
            from g in groups
            select new { Name = m.Key.Name,
                        LimpIsbn = g.Key.LimpIsbn,
                        CasedIsbn = g.Key.CasedIsbm,
                        LastOrder = g.Max(x => x)})
            .OrderBy(e=>e.LastOrder).Take(5);

Linq To Entities Group按加入时的最大日期

2 个答案: