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我面临一个场景，我必须根据许多对象过滤单个对象。

例如，我有一个Grocery对象，它包含 Fruit 和 Vegetable 属性。然后我有单独的水果和蔬菜对象。

我的目标是这样的：

var groceryList = from grocery in Grocery.ToList()
                  from fruit in Fruit.ToList()
                  from veggie in Vegetable.ToList()
                  where (grocery.fruitId = fruit.fruitId)
                  where (grocery.vegId = veggie.vegId)
                  select (grocery);

我面临的问题是水果和蔬菜对象是空的。 空，我的意思是他们的列表计数为 0，我只想在填充过滤器列表时应用过滤器。

由于对象为空，我也无法使用类似的东西：

var groceryList = from grocery in Grocery.ToList()
                  from fruit in Fruit.ToList()
                  from veggie in Vegetable.ToList()
                  where (grocery.fruitId = fruit.fruitId || fruit.fruitId == String.Empty)
                  where (grocery.vegId = veggie.vegId || veggie.vegId == String.Empty)
                  select (grocery);

所以，我打算检查水果和蔬菜列表计数......并将它们过滤为连续过滤的Grocery对象上的单独表达式。

但是有没有办法在单个查询表达式中有空对象的情况下仍然获取列表？

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5 回答 5

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尝试以下操作：

var joined = grocery.Join(fruit, g => g.fruitId,
                                 f => f.fruitId,
                                 (g, f) => new Grocery() { /*set grocery properties*/ }).
                Join(veggie, g => g.vegId,
                             v => v.vegId,
                             (g, v) => new Grocery() { /*set grocery properties*/ });

在我说过设置杂货属性的地方，您可以从选择器的 g、f、v 变量中设置杂货对象的属性。感兴趣的显然是设置g.fruitId = f.fruitId和g.vegeId = v.vegeId。

于 2009-09-17T03:06:01.253 回答
0

我认为LINQ GroupJoin 运算符会在这里为您提供帮助。它类似于 TSQLLEFT OUTER JOIN

于 2009-09-17T03:09:29.303 回答
0 
IEnumerable<Grocery> query = Grocery

if (Fruit != null)
{
  query = query.Where(grocery =>
    Fruit.Any(fruit => fruit.FruitId == grocery.FruitId));
}

if (Vegetable != null)
{
  query = query.Where(grocery =>
    Vegetable.Any(veggie => veggie.VegetableId == grocery.VegetableId));
}

List<Grocery> results = query.ToList();
于 2009-09-17T03:10:21.127 回答
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var groceryList =
  from grocery in Grocery.ToList()
  join fruit in Fruit.ToList()
       on grocery.fruidId equals fruit.fruitId
       into groceryFruits
  join veggie in Vegetable.ToList()
       on grocery.vegId equals veggie.vegId
       into groceryVeggies
  where ... // filter as needed
  select new
  {
    Grocery = grocery,
    GroceryFruits = groceryFruits,
    GroceryVeggies = groceryVeggies
  };
于 2009-09-17T03:19:55.193 回答
0

为此，您必须使用leftouter join（如TSQL）。在技​​巧的查询下方

private void test()
{
    var grocery = new List<groceryy>() { new groceryy { fruitId = 1, vegid = 1, name = "s" }, new groceryy { fruitId = 2, vegid = 2, name = "a" }, new groceryy { fruitId = 3, vegid = 3, name = "h" } };
    var fruit = new List<fruitt>() { new fruitt { fruitId = 1, fname = "s" }, new fruitt { fruitId = 2, fname = "a" } };
    var veggie = new List<veggiee>() { new veggiee { vegid = 1, vname = "s" }, new veggiee { vegid = 2, vname = "a" } };
    //var fruit= new List<fruitt>();
    //var veggie = new List<veggiee>();

    var result = from g in grocery
                 join f in fruit on g.fruitId equals f.fruitId into tempFruit
                 join v in veggie on g.vegid equals v.vegid into tempVegg
                 from joinedFruit in tempFruit.DefaultIfEmpty()
                 from joinedVegg in tempVegg.DefaultIfEmpty()
                 select new { g.fruitId, g.vegid, fname = ((joinedFruit == null) ? string.Empty : joinedFruit.fname), vname = ((joinedVegg == null) ? string.Empty : joinedVegg.vname) };

    foreach (var outt in result)
        Console.WriteLine(outt.fruitId + "  " + outt.vegid  + "  " + outt.fname  + "  " + outt.vname);
}
public class groceryy
{
    public int fruitId;
    public int vegid;
    public string name;
}
public class fruitt
{
    public int fruitId;
    public string fname;
}
public class veggiee
{
    public int vegid;
    public string vname;
}

编辑： 这是示例结果

1 1 秒

2 2 氨基酸

3 3

于 2009-09-17T06:55:20.547 回答