Question

我需要一个可以在创建匿名类型时调用的可重用函数。

我尝试了以下内容，但是从EntityFramework转换函数到表达式时出错。

任何人都可以帮助我。

var query2 = (from parts in cabinetOrderParts
              join header in headers
              on parts.SQLHeaderID equals header.SQLHeaderID
              join order in orders
              on parts.SQLOrderID equals order.SQLOrderID
              where parts.SQLHeaderID == sqlheaderid
              orderby parts.SQLOrderID
              orderby parts.CabinetDoorPartsID
              select new
              {
                  Height = doit.GetHeight(parts, order),
                  //a number of other parts, header and order fields omitted.

              });

public static class doit
{
    public static Expression<Func<ICabinetDoorPart, ISQLOrder, decimal?>> GetHeight(ICabinetDoorPart part, ISQLOrder order)
    {
        //parts.CutToHeight.HasValue ? parts.CutToHeight : parts.Height
        Expression condition = Expression.Condition(
            Expression.Constant(part.CutToHeight.HasValue),       Expression.Constant(part.CutToHeight), Expression.Constant(part.Height));
        var selector = Expression.Lambda<Func<ICabinetDoorPart, ISQLOrder, decimal?>>(condition);
        return selector.Compile();
    }
}

更新：我使用了Debugview并捕获了实体框架正在使用的表达式。

.Lambda   #Lambda10<System.Func`2[<>f__AnonymousType1`2[<>f__AnonymousType0`2[Interfaces    .Shiloh.ICabinetDoorPart,Interfaces.SQLFilePro.ISQLHeader],Interfaces.SQLFilePro.ISQLOrder],<>f__AnonymousType2`1[System.Nullable`1[System.Decimal]]]>  (<>f__AnonymousType1`2[<>f__AnonymousType0`2[Interfaces.Shiloh.ICabinetDoorPar t,Interfaces.SQLFilePro.ISQLHeader],Interfaces.SQLFilePro.ISQLOrder]   $<>h__TransparentIdentifier1)
{
    .New <>f__AnonymousType2`1[System.Nullable`1[System.Decimal]](.If (
            ((($<>h__TransparentIdentifier1.<>h__TransparentIdentifier0).parts).CutToHeight).HasValue
        ) {
            (($<>h__TransparentIdentifier1.<>h__TransparentIdentifier0).parts).CutToHeight
        } .Else {
        (($<>h__TransparentIdentifier1.<>h__TransparentIdentifier0).parts).Height
        })
}

我认为这与c＃

相似

public static Expression<Func<object[], decimal?>> GetHeight(object[] value)
    {
        var exp = Expression.New(new { Height = new decimal?() }.GetType().GetConstructors()[0],
                                    Expression.Constant(10));
        var selector = Expression.Lambda<Func<object[], decimal?>>(exp);
        return selector;
    }

但仍然没有快乐！

EntityFramework如何编写要在匿名类型

0 个答案: