无法将类型 A 转换为类型 B。LINQ to Entities 仅支持转换 EDM 原语或枚举类型

Question

我在我的项目中首先使用 EF 代码，我有以下实体：

public class WorkcenterCapacity : ITimePeriodEntity
{
    public int Id { get; set; }
    public decimal AvailableCapacity { get; set; }
    public DateTime FromTime { get; set; }
    public DateTime ToTime { get; set; }
}
public interface ITimePeriodEntity
{
    DateTime FromTime { get; set; }
    DateTime ToTime { get; set; }
}

我也用 PredicateBuilder 做了一个动态谓词。出于可用性目的，我定义了以下通用 class：

public static class CropPredicateBuilder<T> where T : ITimePeriodEntity
{
    public static Expression<Func<T, bool>> Creat(DateTime windowStart,
                                                  DateTime windowFinish)
    {
        var result = PredicateBuilder.False<T>();
        Expression<Func<T, bool>> completelyInWindowRanges =
            x => x.FromTime >= windowStart && x.ToTime <= windowFinish;
        Expression<Func<T, bool>> startIsInWindowRanges =
            x => x.FromTime >= windowStart && x.FromTime <= windowFinish;
        Expression<Func<T, bool>> finishIsInWindowRanges =
            x => x.ToTime >= windowStart && x.ToTime <= windowFinish;
        Expression<Func<T, bool>> overlapDateRangeWindow =
            x => x.FromTime <= windowStart && x.ToTime >= windowFinish;

        return result.Or(completelyInWindowRanges)
            .Or(startIsInWindowRanges)
            .Or(finishIsInWindowRanges)
            .Or(overlapDateRangeWindow);
    }
}

并按如下方式使用它：

var predicate = CropPredicateBuilder<WorkcenterCapacity>
               .Creat(DateTime.Now,DateTime.Now.AddDays(10));

var workcenterCapacities = dbContext.WorkcenterCapacities
            .AsNoTracking()
            .Where(predicate)
            .AsExpandable()
            .ToList();

但是当我运行它时，我得到以下错误：

Unable to cast the type 'WorkcenterCapacity' to type 'ITimePeriodEntity'. LINQ to Entities only supports casting EDM primitive or enumeration types.

我该如何解决这个问题？

Answer 1

这样试试

where T : class, ITimePeriodEntity

要第一个约束是class。我认为这是要确定的。

Answer 2

顺便说一句，这也可以解决问题，而且速度可能更快。

public static class CropPredicateBuilder<T> where T : class, ITimePeriodEntity
{
    public static Expression<Func<T, bool>> Creat(DateTime windowStart,
                                                  DateTime windowFinish)
    {
        var result = PredicateBuilder.False<T>();
        Expression<Func<T, bool>> startBeforeToTime =
            x => windowStart <= x.ToTime;
        Expression<Func<T, bool>> finishAfterFromTime =
            x =>  windowFinish >= x.FromTime;

        return result.Or(startBeforeToTime)
            .Or(finishAfterFromTime);
    }
}

无法将类型 A 转换为类型 B。LINQ to Entities 仅支持转换 EDM 原语或枚举类型

Unable to cast the type A to type B. LINQ to Entities only supports casting EDM primitive or enumeration types

c#

linq-to-entities

entity-framework

predicatebuilder

ef-code-first