Question

所以我使用EF并尝试进行非常简单的数据库调用。我对其他对象进行了相同的调用，但没有得到这种行为。行为是，如果我在where语句中链接两个子句，我不再得到任何结果。以下是一些示例代码：

public List<Widgets> FindAll(long? relatedGadgetID)
using (myDBContext db = new myDBContext())
{
    return db.Widgets.Where(w => w.Deleted == false && w.GadgetID == relatedGadgetID).ToList();
    // This does not get any of the objects in the database
}

public List<Widgets> FindAll(long? relatedGadgetID)
using (myDBContext db = new myDBContext())
{
    return db.Widgets.Where(w => w.Deleted == false).Where(w => w.GadgetID == relatedGadgetID).ToList();
    // This does not get any of the objects in the database
}

public List<Widgets> FindAll(long? relatedGadgetID)
using (myDBContext db = new myDBContext())
{
    var x =  db.Widgets.Where(w => w.Deleted == false).ToList();
    return x.Where(w => w.GadgetID == relatedGadgetID).ToList();
    // This DOES!
}

为什么？

编辑：关闭评论，我尝试了解决方法，但它仍然无法正常工作。这是我尝试过的，我做错了吗？

public List<Widgets> FindAll(long? relatedGadgetID)
using (myDBContext db = new myDBContext())
{
    return db.Widgets.Where(w => w.Deleted == false && (relatedGadgetID == null ? w.GadgetID == null : w.GadgetID == relatedGadgetID)).ToList();
    // Still doesn't work =(
}

Edit2：尝试了另一个修复，仍然没有运气。

public List<Widgets> FindAll(long? relatedGadgetID)
using (myDBContext db = new myDBContext())
{
    return db.Widgets.Where(w => (w.Deleted == false) && (w.GadgetID == relatedGadgetID || (relatedGadgetID == null && w.GadgetID == null))).ToList();
    // Still doesn't work =(
}

Edit3：再次尝试了Object.Equals。

public List<Widgets> FindAll(long? relatedGadgetID)
using (myDBContext db = new myDBContext())
{
    return db.Widgets.Where(w => w.Deleted == false && w.GadgetID.Equals(relatedGadgetID)).ToList();
    // Still doesn't work =(
}

Answer 1

在我试图尽早修复它时，我意外地将我的类属性更改为不可为空，而表列仍然是。一旦我意识到这一点，原始尝试仍然有相同的结果，但解决方法工作。我最终使用了第一个编辑解决方法。谢谢碎玻璃！

条款奇怪行为的实体框架

1 个答案: