使用Linq to Entities'包含()'解决方法？

我正在尝试使用Silverlight ADO.Net数据服务客户端api(以及Linq To Entities)创建一个使用where子句中的id列表的查询.有没有人知道Contains不受支持的解决方法？

我想做这样的事情:

List txnIds = new List();
// Fill list 

var q = from t in svc.OpenTransaction
        where txnIds.Contains(t.OpenTransactionId)
        select t;

---

试过这个:

var q = from t in svc.OpenTransaction
where txnIds.Any(tt => tt == t.OpenTransactionId)
select t;

但得到"方法'任何'不受支持".

1> Shimmy..：

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更新: EF≥4 ">Contains直接支持(Checkout ">Any),因此您不需要任何解决方法.

public static IQueryable WhereIn
  (
    this ObjectQuery query,
    Expression> selector,
    IEnumerable collection
  )
{
  if (selector == null) throw new ArgumentNullException("selector");
  if (collection == null) throw new ArgumentNullException("collection");
  if (!collection.Any()) 
    return query.Where(t => false);

  ParameterExpression p = selector.Parameters.Single();

  IEnumerable equals = collection.Select(value =>
     (Expression)Expression.Equal(selector.Body,
          Expression.Constant(value, typeof(TValue))));

  Expression body = equals.Aggregate((accumulate, equal) =>
      Expression.Or(accumulate, equal));

  return query.Where(Expression.Lambda>(body, p));
}

//Optional - to allow static collection:
public static IQueryable WhereIn
  (
    this ObjectQuery query,
    Expression> selector,
    params TValue[] collection
  )
{
  return WhereIn(query, selector, (IEnumerable)collection);
}

用法:

public static void Main()
{
  using (MyObjectContext context = new MyObjectContext())
  {
    //Using method 1 - collection provided as collection
    var contacts1 =
      context.Contacts.WhereIn(c => c.Name, GetContactNames());

    //Using method 2 - collection provided statically
    var contacts2 = context.Contacts.WhereIn(c => c.Name,
      "Contact1",
      "Contact2",
      "Contact3",
      "Contact4"
      );
  }
}

---

警告; 当arg是大集合(我的是8500项目列表)时,堆栈溢出.你可能认为通过这样的列表很疯狂,但我认为这暴露了这种方法的一个缺陷.

---

如果我错了,请纠正我.但这意味着当传递的集合(过滤器)是一个空集时,它基本上会导致所有数据导致它只返回查询参数.我期待它过滤所有价值,有没有办法做到这一点？

2> Rob Fonseca-..：

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您可以在手边编写一些e-sql(请注意关键字"it"):

return CurrentDataSource.Product.Where("it.ID IN {4,5,6}"); 

这是我用来从集合YMMV生成一些e-sql的代码:

string[] ids = orders.Select(x=>x.ProductID.ToString()).ToArray();
return CurrentDataSource.Products.Where("it.ID IN {" + string.Join(",", ids) + "}");

3> James Bloome..：

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来自MSDN:

static Expression> BuildContainsExpression(
    Expression> valueSelector, IEnumerable values)
{
    if (null == valueSelector) { throw new ArgumentNullException("valueSelector"); }
    if (null == values) { throw new ArgumentNullException("values"); }
    ParameterExpression p = valueSelector.Parameters.Single();

    // p => valueSelector(p) == values[0] || valueSelector(p) == ...
    if (!values.Any())
    {
        return e => false;
    }

    var equals = values.Select(
             value => (Expression)Expression.Equal(valueSelector.Body, Expression.Constant(value, typeof(TValue))));

    var body = equals.Aggregate((accumulate, equal) => Expression.Or(accumulate, equal));

    return Expression.Lambda>(body, p);
} 

并且查询变为:

var query2 = context.Entities.Where(BuildContainsExpression(e => e.ID, ids));

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如果你想做一个'Not contains',只需在BuildContainsExpression方法中进行以下编辑: - Expression.Equal变为Expression.NotEqual - Expression.Or变为Expression.And