[英]How to perform a join of two sets and populate navigation properties
假設我有兩個課, Teapot
和Cup
:
public class Teapot
{
[Key]
[Column("Id", TypeName = "int")]
public int Id { get; set; }
public int MaterialId { get; set; }
public int ColorId { get; set; }
[ForeignKey("MaterialId")]
public virtual Material Material { get; set; }
[ForeignKey("ColorId")]
public virtual Color Color { get; set; }
}
和
public class Cup
{
[Key]
[Column("Id", TypeName = "int")]
public int Id { get; set; }
public int MaterialId { get; set; }
public int ColorId { get; set; }
[ForeignKey("MaterialId")]
public virtual Material Material { get; set; }
[ForeignKey("ColorId")]
public virtual Color Color { get; set; }
}
這是我的ViewModel:
namespace ViewModel.Data
{
public class TeapotsWithInfo
{
public Model.Data.Teapot Teapot { get; set; }
public Model.Data.Cup Cup { get; set; }
}
}
對於我的ViewModel
,我需要對MaterialId和ColorId執行聯接,並包含一些導航屬性,例如Teapot.Material.Manufacturer
。 因此,我嘗試了以下查詢:
這將引發“ LINQ to Entities僅支持轉換EDM基本類型或枚舉類型”
(from t in db.Teapots join c in db.Cups on new { t.MaterialId, t.ColorId } equals new { c.MaterialId, c.ColorId } where t.Id == id select new ViewModel.Data.TeapotsWithInfo { Teapot = t, Cup = c }) .Include(t => t.Material.Manufacturer).SingleOrDefault();
這似乎忽略了Include
(from t in db.Teapots.Include(t => t.Material.Manufacturer) join c in db.Cups on new { t.MaterialId, t.ColorId } equals new { c.MaterialId, c.ColorId } where t.Id == id select new ViewModel.Data.TeapotsWithInfo { Teapot = t, Cup = c }).SingleOrDefault();
現在,我在這里找到了一些答案,建議先進行枚舉,然后再執行另一個選擇,但我寧願一口氣捕獲數據。
您遇到的困難包括導航性能,因為與連接的查詢或預測忽略預先加載(見本 )。
不幸的是,您將需要做的事情似乎是避免的:首先從數據庫中提取數據,然后再進行其他選擇以構建ViewModel(它將從原始查詢中加載關系)。 但是,由於沒有從數據庫中執行額外的加載,因此,附加選擇應該是相當瑣碎的操作,可枚舉應僅包含一個項目。
(from t in db.Teapots.Include(t => t.Material.Manufacturer)
join c in db.Cups
on new { t.MaterialId, t.ColorId } equals new { c.MaterialId, c.ColorId }
where t.Id == id
select new
{
Teapot = t,
Cup = c,
Material = t.Material,
Manufacturer = t.Material.Manufacturer,
})
.AsEnumerable()
.Select(a => new ViewModel.Data.TeapotsWithInfo
{
Teapot = a.Teapot,
Cup = a.Cup
})
.SingleOrDefault();
資源
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