Question

我有类似的事情

if (this.IncludeGuestlist)
{
    return from tn in tnQuery
           join gi in bl.Database.GuestlistItems on tn.Id equals gi.TicketNumberId into gj
           from giJoined in gj.DefaultIfEmpty()
           select new TicketNumberTempDTO()
           {
               Id = tn.Id,
               LookupId = tn.LookupId,
               CheckingId = tn.CheckingId,
               GuestlistName = giJoined.GuestlistDefinition.Name
           };
}
else
{
    return from tn in tnQuery               
           select new TicketNumberTempDTO()
           {
               Id = tn.Id,
               LookupId = tn.LookupId,
               CheckingId = tn.CheckingId
           };
}

鉴于我不希望在没有必要的情况下发生左连接，是否有可能统一这个以便我不必写两次选择？

[e.g。写下＆＃34; base＆＃34; select（Id，LookupId，CheckingId），如果IncludeGuestlist为true，则将join和GuestlistName添加到现有的select]

编辑：简化模型如下，tnQuery是动态构建的IQueryable

public class TicketNumber
{     
    public int Id { get; set; }
    public string LookupId { get; set; }
    public string CheckingId { get; set; }
}

public class GuestlistItem
{     
    public int Id { get; set; }

    public int GuestlistDefinitionId { get; set; }
    public virtual GuestlistDefinition GuestlistDefinition { get; set; }

    public int TicketNumberId { get; set; }
    public virtual TicketNumber TicketNumber { get; set; }
}

public class GuestlistDefinition
{     
    public int Id { get; set; }
    public string Name {get; set; }
}

Answer 1

我将新的导航属性添加到TicketNumber：

public class TicketNumber
{     
    // your properties

    public virtual List<GuestlistItem> GuestListItems { get; set; }
}

然后：

var query = context.Set<TicketNumber>().AsQueryable();

if (IncludeGuestlist)
{
    query = query.Include(tn => tn.GuestListItems);
}

var ticketNumbers = query.Where(/* do your filter logic here */).ToList(); // You can use SingleOrDefault instead. It depends on your case.

return ticketNumbers
    .Select(tn => new TicketNumberTempDTO
    {
        // make your assignation logic
        GuestlistName = GuestListItems?.FirstOrDefault()?.Name
    }).ToList();

使用此条件包含，仅在必要时才进行连接。

注意：我根据您的数据模型做了一些假设（您的关系的基数是什么？）。不要犹豫要精确一些事情，这样我才能更明确。

动态左连接实体框架6

1 个答案: