c# - LINQ 编译查询选择求和多列

Question

我有一张桌子：

ForObjectTypeID (short, PK)
ForObjectID (int, PK)
UserID (int, PK)
Upvote (bool)
ShadowBannedVote (bool)

给定一个ObjectTypeIDand ObjectID，我希望返回一个Tuple<int, int, int>各自的值是：

• 总投票数：记录的总数ShadowBannedVote == false
• Total Upvotes：记录总数Upvote == true && ShadowBannedVote == false
• 影子禁止投票总数：记录的总数ShadowBannedVote == true

它需要是单个编译查询，而不是分解为多个查询。据我所知，我只是无法弄清楚如何在返回值中执行总和和计数。

public static readonly Func<DBContext, ObjectType, int, Tuple<int, int, int>> GetTotalVotes = CompiledQuery.Compile(
    (DBContext db, ObjectType forObjectType, int forObjectID) =>
    db.UserVotes.Where(c => c.ForObjectTypeID == (short)forObjectType && c.ForObjectID == forObjectID)
    .Select(c=> new {c.Upvote, c.ShadowBannedVote}).Select(c=> new Tuple<int, int, in>(0, 0, 0)));

Answer 1

您可以尝试按常数分组，求和并取结果，即类似

  public static readonly Func<DBContext, ObjectType, int, Tuple<int, int, int>> GetTotalVotes = CompiledQuery.Compile(
        (DBContext db, ObjectType forObjectType, int forObjectID) 
   => 
   db.UserVotes
    .Where(c => c.ForObjectTypeID == (short)forObjectType 
             && c.ForObjectID == forObjectID)
    .Select(c => new { c.Upvote, c.ShadowBannedVote })
    .GroupBy(c => 1)
    .Select(c => new Tuple<int, int, int>(
        c.Count(r => !r.ShadowBannedVote), 
        c.Count(r => r.Upvote && !r.ShadowBannedVote), 
        c.Count(r => r.ShadowBannedVote)
    )).Single());

Answer 2

有兴趣看看这是否可能，但一种解决方案是：

public static readonly Func<DBContext, ObjectType, int, IEnumerable<Tuple<bool, bool>>> GetTotalVotes = CompiledQuery.Compile(
    (DBContext db, ObjectType forObjectType, int forObjectID) =>
    db.UserVotes.Where(c => c.ForObjectTypeID == (short)forObjectType && c.ForObjectID == forObjectID)
    .Select(c=> new Tuple<bool, bool>(c.Upvote, c.ShadowBannedVote)));

然后简单地计算出应用程序逻辑中的数字。