EF Core无法翻译，将在本地进行评估

Question

我在EF Core 1.1.2中有一个在客户端评估的查询，想知道是否有更好的方法将其转换为sql？

查询：

from l in _ctx.Locations
  join i in _ctx.Inventories on l.Id equals i.LocationId
  join it in _ctx.Items on i.ItemId equals it.Id
  where l.ProjectId == projectid
  group i by new {l.Id, l.LHA} into il
  select new InventoryLocations() {
      Id= il.Key.Id,
      LHA = il.Key.LHA,
      FlaggedItems = il.Any(x=>x.Item != null && x.Item.Flagged)
  }

如果没有，我还有什么其他选择？

• 据我所知，仍然无法映射视图。
• FromSQL（）方法只能返回仅在上下文中已知的类型，例如，我不能将一个模型标记为[NotMapped]。
• 不能选择返回到ef6，因为.net核心是目标框架。

楷模：

public class Location
{
    public Guid Id { get; set; }

    [ForeignKey("Project")]
    public Guid ProjectId { get; set; }
    public Project Project {get; set; }
    public string Name { get; set; }
    public string LHA { get; set; }

    [ForeignKey("ScanUser")]
    public Guid? ScanUserId { get; set; }
    public User ScanUser { get; set; }
    [ForeignKey("CheckUser")]
    public Guid? CheckUserId { get; set; }
    public User CheckUser { get; set; }

    [ForeignKey("GroupLeader")]
    public Guid? GroupLeaderId { get; set; }
    public User GroupLeader { get; set; }
    public int State { get; set; }
}

public class Inventory
{
    public Guid Id { get; set; }

    [ForeignKey("Project")]
    public Guid ProjectId { get; set; }
    public Project Project {get; set; }
    public string EANCode { get; set; }
    [ForeignKey("Location")]
    public Guid LocationId { get; set; }
    public Location Location { get; set; }
    public Double ScanQty { get; set; }
    [ForeignKey("ScanUser")]
    public Guid? ScanUserId { get; set; }
    public User ScanUser { get; set; }
    public DateTime? ScanDate { get; set; }
    [ForeignKey("Item")]
    public Guid? ItemId { get; set; }
    public Item Item { get; set; }

    [ForeignKey("InventoryTask")]
    public Guid? InventoryTaskId { get; set; }
    public InventoryTask InventoryTask { get; set; }

    [ForeignKey("CheckUser")]
    public Guid? CheckUserId { get; set; }
    public User CheckUser { get; set; }
    public DateTime? CheckDate { get; set; }
    public Double PrevQty { get; set; }
}

public class Item
{
    public Guid Id { get; set; }
    [ForeignKey("Project")]
    public Guid ProjectId { get; set; }
    public Project Project {get; set; }
    public string ItemNo { get; set; }
    public string EANCode { get; set; }
    public string Name { get; set; }
    public Double Price { get; set; }
    public bool Deleted { get; set; }
    public DateTime ChangeTime { get; set; }

    public Double BaseQty { get; set; }
    public bool Flagged { get; set; }
}

Answer 1

当前（在传入的EF Core v.2.0中也是如此），GroupBy查询是在本地处理的，因此关键是尽可能避免查询。

您的查询似乎符合条件-无需先将数据集与联接相乘，然后再将其分组。

我注意到您在实体中仅使用参考导航属性和FK，基本上像数据库表记录和SQL。但是EF允许您还定义相应的集合导航属性，该属性使您可以从逻辑根目录开始查询，从而消除了联接和分组依据。

如果您从Location到定义导航属性Inventory

public class Location
{
    // ...
    public ICollection<Inventory> Inventories { get; set; }
}

那么等效查询可以很简单：

from loc in _ctx.Locations
where loc.ProjectId == projectid
select new InventoryLocations()
{
    Id = loc.Id,
    LHA = loc.LHA,
    FlaggedItems = loc.Inventories.Any(inv => inv.Item != null && inv.Item.Flagged)
}

它将完全转换为SQL。

如果由于某种原因您无法创建上述集合导航属性，则仍然可以从位置开始并将它们与库存手动关联：

from loc in _ctx.Locations
where loc.ProjectId == projectid
select new InventoryLocations()
{
    Id = loc.Id,
    LHA = loc.LHA,
    FlaggedItems = _ctx.Inventories.Any(inv => loc.Id == inv.LocationId && inv.Item != null && inv.Item.Flagged)
}