使用Linq to Entities'包含()'解决方法?

.net-3.5 c# entity-framework linq linq-to-entities

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<long?> txnIds = new List<long?>();
// 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<long>(tt => tt == t.OpenTransactionId)
select t;

但得到“方法'任何'不受支持”。

一般承认的答案

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

public static IQueryable<TEntity> WhereIn<TEntity, TValue>
  (
    this ObjectQuery<TEntity> query,
    Expression<Func<TEntity, TValue>> selector,
    IEnumerable<TValue> 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<Expression> 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<Func<TEntity, bool>>(body, p));
}

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

热门答案

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) + "}");



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这个KB合法吗? 是的,了解原因
许可下: CC-BY-SA with attribution
不隶属于 Stack Overflow
这个KB合法吗? 是的,了解原因