C# 使用导航属性和Where子句的Linq查询

我正在尝试使用导航属性组合linq查询。我正在从3个实体中选择属性：

• 储物柜
• 截面柱
• 合同

我需要符合以下所有条件的储物柜表中的所有行：储物柜类型ID=“308”，.OutOfOrder！=true，x.SectionColumn.SectionId==“52”）

下面的查询没有条件x.SectionColumn.SectionId==“52”，它可以正常工作并返回我所需要的内容，但节id为任意值的行会像我预期的那样返回

    from l in Lockers.Where(x => x.LockerTypeId == "308" && x.OutOfOrder != 
    true).DefaultIfEmpty()
               select new 
                {
                   ColumnNumber = l.ColumnNumber,
                   LockerTypeId = l.LockerTypeId,
                   OutOfOrder = l.OutOfOrder,
                   Rented = l.Contracts.Select(x => x.Contract_ID < 0 ?                   
                     false : true).FirstOrDefault(),
                   Section = l.SectionColumn.SectionId
                   }

---

如果您能帮助我正确编写此查询，我将不胜感激。

首先，如果您坚持使用纯LINQ，您的代码可能会更直接一些。在这种情况下，您的代码应该如下所示

 var results = from l in Lockers
               where l.LockerTypeId == "308" && l.OutOfOrder != true && l.SectionColumn.SectionId == "52"
               select new 
               {
                    ColumnNumber = l.ColumnNumber,
                    LockerTypeId = l.LockerTypeId,
                    OutOfOrder = l.OutOfOrder,
                    Rented = l.Contracts.Select(x => x.Contract_ID < 0 ? false : true).FirstOrDefault(),
                    Section = l.SectionColumn.SectionId
               }

---

请编辑第二个代码示例。那里没有

SectionId

。Section=l.SectionColumn！=null？l.SectionColumn.SectionId？0:0如果SectionColumn在表架构中为allow null？在访问l.SectionColumn.SectionId之前，必须检查l.SectionColumn是否等于null，只要某些SectionColumn为null值，在访问l.SectionColumn.SectionId之前，此解决方案不可能是真的。您必须检查l.SectionColumn不等于null谢谢-我会尝试一下。@。不知道为什么lambda版本不起作用。谢谢你的建议。

 var results = from l in Lockers
               where l.LockerTypeId == "308" && l.OutOfOrder != true && l.SectionColumn.SectionId == "52"
               select new 
               {
                    ColumnNumber = l.ColumnNumber,
                    LockerTypeId = l.LockerTypeId,
                    OutOfOrder = l.OutOfOrder,
                    Rented = l.Contracts.Select(x => x.Contract_ID < 0 ? false : true).FirstOrDefault(),
                    Section = l.SectionColumn.SectionId
               }

 var results = from l in Lockers
               let sectionId = (l.SectionColumn != null) ? l.SectionColumn.SectionId : null
               where l.LockerTypeId == "308" && l.OutOfOrder != true && sectionId == "52"
               select new 
               {
                    ColumnNumber = l.ColumnNumber,
                    LockerTypeId = l.LockerTypeId,
                    OutOfOrder = l.OutOfOrder,
                    Rented = l.Contracts.Select(x => x.Contract_ID < 0 ? false : true).FirstOrDefault(),
                    Section = l.SectionColumn.SectionId
               }