Question

我正在玩Subsonic 3.0 SimpleRepository并尝试使用一个linq查询获取菜单和菜单项，但是菜单项总是空的

菜单

public class Menu
{
    public Menu()
    {
        MenuId = 0;
        MenuName = "";
        MenuItems = null;
    }
    public int MenuId { get; set; }
    public string MenuName { get; set; }
    public MenuItem MenuItems { get; set; }
}

菜单项

public class MenuItem
{
    public MenuItem()
    {
        MenuItemId = 0;
        MenuId = 0;
        MenuItemName = "";
    }
    public int MenuItemId { get; set; }
    public int MenuId { get; set; }
    public string MenuItemName { get; set; }
}

Linq查询

var menus =  from m in _repo.All<Menu>()
             from mi in _repo.All<MenuItem>()
             where m.MenuItems.MenuItemId == mi.MenuItemId
             select new Menu
             {
                 MenuId = m.MenuId,
                 MenuName = m.MenuName,
                 MenuItems = {
                             MenuItemId = mi.MenuItemId,
                             MenuItemName = mi.MenuItemName
                        }
             };

有人可以告诉我这里我做错了什么吗？

Answer 1

我想我找到了这个问题的实际答案。我一直在SubSonic源代码中翻找，发现在将datareader映射到对象时有两种类型的对象投影：一种用于匿名类型和分组，另一种用于其他一切：

这是一个片段：SubSonic.Linq.Structure.DbQueryProvider的第269 - 298行

IEnumerable<T> result;
Type type = typeof (T);
//this is so hacky - the issue is that the Projector below uses Expression.Convert, which is a bottleneck
//it's about 10x slower than our ToEnumerable. Our ToEnumerable, however, stumbles on Anon types and groupings
//since it doesn't know how to instantiate them (I tried - not smart enough). So we do some trickery here.
    if (type.Name.Contains("AnonymousType") || type.Name.StartsWith("Grouping`") || type.FullName.StartsWith("System.")) {
    var reader = _provider.ExecuteReader(cmd);
    result = Project(reader, query.Projector);
    } else
    {
        using (var reader = _provider.ExecuteReader(cmd))
        {
            //use our reader stuff
            //thanks to Pascal LaCroix for the help here...
            var resultType = typeof (T);
            if (resultType.IsValueType)
            {
                result = reader.ToEnumerableValueType<T>();
            }
            else
            {
                result = reader.ToEnumerable<T>();
            }
        }
    }
    return result;

事实证明，SubSonic ToEnumerable会尝试将datareader中的列名与您尝试投影到的对象中的属性相匹配。我的Linq的SQL查询如下所示：

SELECT [t0].[Id], [t0].[ProductId], [t0].[ReleaseDate], [t0].[ReleasedBy], [t0].[ReleaseNumber], [t0].[RevisionNumber], [t0].[c0]
FROM (
  SELECT [t1].[Id], [t1].[ProductId], [t1].[ReleaseDate], [t1].[ReleasedBy], [t1].[ReleaseNumber], [t1].[RevisionNumber], (
    SELECT COUNT(*)
    FROM [dbo].[Install] AS t2
    WHERE ([t2].[ReleaseId] = [t1].[Id])
    ) AS c0
  FROM [dbo].[Release] AS t1
  ) AS t0
WHERE ([t0].[ProductId] = 2)

注意[t0]。[c0]与我的属性名称NumberOfInstalls不同。所以c0的值永远不会被投射到我的对象中。

固定：您可以简单地取出if语句并使用10x较慢的投影，一切都会有效。

Answer 2

我认为你在这里做错了什么。这似乎是Subsonic 3.0的一个问题。我现在有一个问题，我没有得到here的答案。我最近也尝试过更简单的东西。但这也不起作用。

var result = from r in Release.All()
             let i = Install.All().Count(x => x.ReleaseId == r.Id)
             where r.ProductId == productId
             select new ReleaseInfo
             {
                 NumberOfInstalls = i,
                 Id = r.Id,
                 ProductId = r.ProductId,
                 ReleaseNumber = r.ReleaseNumber,
                 RevisionNumber = r.RevisionNumber,
                 ReleaseDate = r.ReleaseDate,
                 ReleasedBy = r.ReleasedBy
             };

安装数量属性未填充，但如果我映射到匿名类型，一切正常：

var result = from r in Release.All()
             let i = Install.All().Count(x => x.ReleaseId == r.Id)
             where r.ProductId == productId
             select new 
             {
                 NumberOfInstalls = i,
                 Id = r.Id,
                 ProductId = r.ProductId,
                 ReleaseNumber = r.ReleaseNumber,
                 RevisionNumber = r.RevisionNumber,
                 ReleaseDate = r.ReleaseDate,
                 ReleasedBy = r.ReleasedBy
             };

如果您将代码更改为以下代码，则可能会有效：

var menus =  from m in _repo.All<Menu>()
             from mi in _repo.All<MenuItem>()
             where m.MenuItems.MenuItemId == mi.MenuItemId
             select new 
             {
                 MenuId = m.MenuId,
                 MenuName = m.MenuName,
                 MenuItems = new {
                             MenuItemId = mi.MenuItemId,
                             MenuItemName = mi.MenuItemName
                        }
             };

由于您希望映射回预定义的对象类型，因此这种方法失败了。也许我们可以从Rob那里得到答案？：）

亚音速3.0和linq

2 个答案: