c# - LINQ 查询以选择与成对数组匹配的行

Question

现在，我有一个名为 TrainingPlan 的类，如下所示:

public class TrainingPlan
{
   public int WorkgroupId { get; set; }
   public int AreaId { get; set; }
}

我得到了这些实例的数组，需要从数据库中加载匹配的训练计划。 WorkgroupId 和 AreaId 基本上构成了一个复合键。我现在正在做的是像这样遍历每个 TrainingPlan:

foreach (TrainingPlan plan in plans)
   LoadPlan(pid, plan.AreaId, plan.WorkgroupId);

然后，LoadPlan 有一个 LINQ 查询来加载单个计划:

var q = from tp in context.TPM_TRAININGPLAN.Include("TPM_TRAININGPLANSOLUTIONS")
        where tp.PROJECTID == pid && tp.AREAID == areaid &&
              tp.WORKGROUPID == workgroupid
              select tp;

return q.FirstOrDefault();

问题:

这可行，但是对于大量计划来说速度非常慢。我相信，如果我可以执行单个 LINQ 查询以同时加载每个 TPM_TRAININGPLAN，这会快得多。

我的问题:

给定一组 TrainingPlan 对象，我如何才能一次加载每个匹配的 WorkgroupId/AreaId 组合？此查询应转换为类似的 SQL 语法:

SELECT * FROM TPM_TRAININGPLANS
WHERE (AREAID, WORKGROUPID) IN ((1, 2), (3, 4), (5, 6), (7, 8));

Answer 1

我使用 Contains 来运行类似于 where-in 的批量过滤器。我设置了您的场景的粗略近似值。单个选择查询实际上比 Contains 运行得更快。我建议您在绑定(bind)数据库的情况下运行类似的测试，看看您的结果如何结束。理想情况下也看看它是如何扩展的。我在 visual studio 2012 中运行 .NET 4.0。我卡在 ToList() 调用中以解决潜在的延迟加载问题。

public class TrainingPlan
{
    public int WorkgroupId { get; set; }
    public int AreaId { get; set; }

    public TrainingPlan(int workGroupId, int areaId)
    {
        WorkgroupId = workGroupId;
        AreaId = areaId;
    }    
}

public class TrainingPlanComparer : IEqualityComparer<TrainingPlan>
{
    public bool Equals(TrainingPlan x, TrainingPlan y)
    {
        //Check whether the compared objects reference the same data. 
        if (x.WorkgroupId == y.WorkgroupId && x.AreaId == y.AreaId) 
            return true;

        return false;                        
    }

    public int GetHashCode(TrainingPlan trainingPlan)
    {            
        if (ReferenceEquals(trainingPlan, null)) 
            return 0;

        int wgHash = trainingPlan.WorkgroupId.GetHashCode();
        int aHash = trainingPlan.AreaId.GetHashCode();

        return wgHash ^ aHash;
    }
}


internal class Class1
{
    private static void Main()
    {
        var plans = new List<TrainingPlan>
            {
                new TrainingPlan(1, 2),
                new TrainingPlan(1, 3),
                new TrainingPlan(2, 1),
                new TrainingPlan(2, 2)
            };

        var filter = new List<TrainingPlan>
            {
                new TrainingPlan(1, 2),
                new TrainingPlan(1, 3),
            };

        Stopwatch resultTimer1 = new Stopwatch();
        resultTimer1.Start();
        var results = plans.Where(plan => filter.Contains(plan, new TrainingPlanComparer())).ToList();
        resultTimer1.Stop();

        Console.WriteLine("Elapsed Time for filtered result {0}", resultTimer1.Elapsed);

        Console.WriteLine("Result count: {0}",results.Count());

        foreach (var item in results)
        {
            Console.WriteLine("WorkGroup: {0}, Area: {1}",item.WorkgroupId, item.AreaId);
        }

        resultTimer1.Reset();

        resultTimer1.Start();
        var result1 = plans.Where(p => p.AreaId == filter[0].AreaId && p.WorkgroupId == filter[0].WorkgroupId).ToList();
        var result2 = plans.Where(p => p.AreaId == filter[1].AreaId && p.WorkgroupId == filter[1].WorkgroupId).ToList();
        resultTimer1.Stop();

        Console.WriteLine("Elapsed time for single query result: {0}",resultTimer1.Elapsed);//single query is faster

        Console.ReadLine();
    }
}