IQueryable-为什么此逻辑失败？

Question

我有一个包含多个表的数据库，在这种情况下，相关的表是

志愿者注册和计划事件：

CREATE TABLE [dbo].[VolunteerSignups] (
    [EventId]      INT            IDENTITY (1, 1) NOT NULL,
    [VolunteerNum] INT            NOT NULL,
    [UserId]       NVARCHAR (128) NULL,
    CONSTRAINT [PK_dbo.VolunteerSignups] PRIMARY KEY CLUSTERED ([EventId] ASC, [VolunteerNum] ASC),
    CONSTRAINT [FK_VolunteerSignups_ProgramEvents_UserId] FOREIGN KEY ([UserId]) REFERENCES [dbo].[AspNetUsers] ([Id]) ON DELETE SET NULL ON UPDATE CASCADE,
    CONSTRAINT [FK_VolunteerSignups_ProgramEvents_EventId] FOREIGN KEY ([EventId]) REFERENCES [dbo].[ProgramEvents] ([EventId])
);
--Triggers and other unneeded info

CREATE TABLE [dbo].[ProgramEvents] (
    [EventId]            INT            IDENTITY (1, 1) NOT NULL,
    [EventTitle]         NVARCHAR (256) NOT NULL,
    [NumVolunteers]      INT            NOT NULL,
    [EventLocation]      NVARCHAR (512) NOT NULL,
    [ServiceDescription] NVARCHAR (MAX) NOT NULL,
    [StartTime]          DATETIME       NOT NULL,
    [EndTime]            DATETIME       NOT NULL,
    CONSTRAINT [PK_dbo.ProgramEvents] PRIMARY KEY CLUSTERED ([EventId] ASC)
);
--Triggers and other unneeded info

总的来说，我所拥有的是一个简单的Web应用程序，它允许进行活动（每个活动可能需要1到N名志愿者），并且志愿者可以报名参加这些活动。 当然，限制是志愿者不能两次报名参加同一活动，并且他们不能报名参加重叠（按时间）的活动。

我几乎完成了MVC应用程序中的所有其他工作，除了志愿者位置要求的后半部分。 我对此有些挣扎，感到恼火，所以我把它留在了最后，而不是让它延迟了整个项目。 但是现在我不能再拖延了，因为除此查询外，其他所有方法都有效。

到目前为止，我有：

[Authorize( Roles = "Administrator, Volunteer" )]
public class VolunteerSignupsController : Controller
{
    private EntitiesDb db = new EntitiesDb();

    // GET: VolunteerSignups
    public async Task<ActionResult> Index()
    {
        var uid = User.Identity.GetUserId();
        var exclude = ( db.VolunteerSignups.Where( o => o.UserId == uid ) );

        var volunteerSignups = db.VolunteerSignups.Include( v => v.AspNetUser ).Include( v => v.ProgramEvent );
        var diff = volunteerSignups.Where( u => ( !exclude.Any( p => p.EventId == u.EventId ) ) && u.UserId == null );

        return View( await diff.ToListAsync() );
    }

此代码可以完美地检索用户尚未注册的事件。 问题在于，它们在注册事件后会返回重叠事件。 因此，我将代码修改为以下内容：

[Authorize( Roles = "Administrator, Volunteer" )]
public class VolunteerSignupsController : Controller
{
    private EntitiesDb db = new EntitiesDb();

    // GET: VolunteerSignups
    public async Task<ActionResult> Index()
    {
        ApplicationDbContext db1 = new ApplicationDbContext();

        var uid = User.Identity.GetUserId();
        var exclude = ( db.VolunteerSignups.Where( o => o.UserId == uid ) );

        var volunteerSignups = db.VolunteerSignups.Include( v => v.AspNetUser ).Include( v => v.ProgramEvent );
        var diff = volunteerSignups.Where( u => ( !exclude.Any( p => p.EventId == u.EventId ) ) && u.UserId == null );

        //GET: ProgramEvents that user has already signed up for
        var alreadyVolunteeredFor = db.ProgramEvents.Where( i => exclude.Any( u => i.EventId == u.EventId ) );

        //GET: ProgramEvents that the user has not signed up for 
        var qualifiesFor = db.ProgramEvents.Where( i => diff.Any( u => i.EventId == u.EventId ) );

        /*Get: VolunteerSignups where the ProgramEvent is one where:
               -The user has not previously volunteered
               -The user has not previously volunteered for a different event where the time overlaps with an event they have not signed up for*/
        var intersect = db.VolunteerSignups.Where( i => ( diff.Any( d => ( d.EventId == i.EventId ) &&
            !qualifiesFor.Any( q => q.EventId == i.EventId &&
             alreadyVolunteeredFor.Any( a => a.EventId == i.EventId &&
               a.EndTime.CompareTo( q.StartTime ) >= 0  &&
               a.StartTime.CompareTo( q.EndTime ) <= 0  ) ) ) ) );

        return View( await intersect.ToListAsync() );
    }

我很确定逻辑失败在于构成intersect的lambda表达式。 在编写过程中，它只返回diff之前所做的完全相同的事情。 但是，我对此所做的任何更改似乎都从列表中删除了所有内容。

编辑以回复mjwillis评论：

diff的数据将是VolunteerSignups行，这些行不会为用户未自愿参与的事件填充。 列是
1. xyz 1 null

2. xyz 2 null

3. abc 1 null

qualifiesFor应与ProgramEvents具有相同的行EventId作为条目diff ：
1. xyz "First Title" 2 "Some Location" "A Description" "11/1/2020 4:00pm" "11/1/2020 7:00pm"
2. abc "Second Title" 1 "A Location" "Some Description" "11/1/2020 5:00pm" "11/1/2020 6:00pm"

alreadyVonteeredFor应符合ProgramEvents排人已自愿参加，没有任何的EventId列应该等于海誓山盟，也不应该是如果任何diff或qualifiesFor ：

1. dsd "Already Volunteered" 1 "Some Place" "Time overlaps" "11/1/2020 3:00pm" "11/1/2020 4:30pm"

我需要的是intersect仅包含diff行3，因为第1行和第2行对应于时间与志愿者已附着的事件重叠的事件。

Answer 1

我找到了解决方案。 问题在于intersect lambda中的a => a.EventId == i.EventId && 。 那是胡说八道，我也不知道为什么会在那儿。 在没有alreadyVolunteeredFor将是qualifiesFor和没有的EventId列将是它的。

正确的答案最终是将intersect的声明更改为：

var intersect = db.VolunteerSignups.Where( i => ( diff.Any( d => ( d.EventId == i.EventId ) &&
            qualifiesFor.Any( q => q.EventId == i.EventId &&
             !alreadyVolunteeredFor.Any( a =>
               (a.EndTime.CompareTo( q.StartTime ) >= 0)  &&
               (a.StartTime.CompareTo( q.EndTime ) <= 0 ) ) ) ) ) );