使用Linq到实体的“Contains()”解决方法?

更新: EF 4支持 Contains 直接(结账 Any ),所以你不需要任何变通方法。

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"
      );
  }
}

你可以随时编写一些e-sql(注意关键字“it”):

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

以下是我用来从集合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) + "}");

来自 MSDN :

static Expression<Func<TElement, bool>> BuildContainsExpression<TElement, TValue>(
    Expression<Func<TElement, TValue>> valueSelector, IEnumerable<TValue> 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<Expression>((accumulate, equal) => Expression.Or(accumulate, equal));

    return Expression.Lambda<Func<TElement, bool>>(body, p);
} 

查询变为:

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

我不确定Silverligth,但在linq对象中,我总是使用any()进行这些查询。

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

为了完成记录,这是我最终使用的代码(为清楚起见省略了错误检查)。..

// How the function is called
var q = (from t in svc.OpenTransaction.Expand("Currency,LineItem")
         select t)
         .Where(BuildContainsExpression<OpenTransaction, long>(tt => tt.OpenTransactionId, txnIds));



 // The function to build the contains expression
   static System.Linq.Expressions.Expression<Func<TElement, bool>> BuildContainsExpression<TElement, TValue>(
                System.Linq.Expressions.Expression<Func<TElement, TValue>> valueSelector, 
                IEnumerable<TValue> values)
        {
            if (null == valueSelector) { throw new ArgumentNullException("valueSelector"); }
            if (null == values) { throw new ArgumentNullException("values"); }
            System.Linq.Expressions.ParameterExpression p = valueSelector.Parameters.Single();

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

            var equals = values.Select(value => (System.Linq.Expressions.Expression)System.Linq.Expressions.Expression.Equal(valueSelector.Body, System.Linq.Expressions.Expression.Constant(value, typeof(TValue))));
            var body = equals.Aggregate<System.Linq.Expressions.Expression>((accumulate, equal) => System.Linq.Expressions.Expression.Or(accumulate, equal));
            return System.Linq.Expressions.Expression.Lambda<Func<TElement, bool>>(body, p);
        }

下面是一个示例,我演示了如何使用DataServiceContext编写基于集合的查询: http://blogs.msdn.com/phaniraj/archive/2008/07/17/set-based-operations-in-ado-net-data-services.aspx

非常感谢。WhereIn扩展方法对我来说已经足够了。我分析了它,并向数据库生成了与e-SQL相同的SQL命令。

public Estado[] GetSomeOtherMore(int[] values)
{
    var result = _context.Estados.WhereIn(args => args.Id, values) ;
    return result.ToArray();
}

生成此内容:

SELECT 
[Extent1].[intIdFRLEstado] AS [intIdFRLEstado], 
[Extent1].[varDescripcion] AS [varDescripcion]
FROM [dbo].[PVN_FRLEstados] AS [Extent1]
WHERE (2 = [Extent1].[intIdFRLEstado]) OR (4 = [Extent1].[intIdFRLEstado]) OR (8 = [Extent1].[intIdFRLEstado])

我认为LINQ中的加入可以是一个漫游。

不过,我还没有测试代码。希望它能有所帮助。干杯。 :-)

List<long?> txnIds = new List<long?>();
// Fill list 

var q = from t in svc.OpenTransaction
        join tID in txtIds on t equals tID
        select t;

加入LINQ:

http://weblogs.asp.net/salimfayad/archive/2008/07/09/linq-to-entities-join-queries.aspx

对不起,新用户,我会对实际答案发表评论,但似乎我还不能这样做?

无论如何,关于BuildContainsExpress()的示例代码的答案,请注意,如果你在数据库实体(即非内存对象)上使用该方法,并且你正在使用IQuery,那么它实际上必须转到数据库,因为它基本上做了很多SQL“或”条件来检查“where in”子句(用SQL Profiler运行它以查看)。

这可能意味着,如果你用多个BuildContainsExpress()来精炼一个IQuery,它不会像你期望的那样将其转换为一个在最后运行的SQL语句。

我们的解决方法是使用多个LINQ连接将其保持为一个SQL调用。

除了选定的答案。

更换 Expression.Or 具有 Expression.OrElse 与Nhibernate一起使用并修复 Unable to cast object of type 'NHibernate.Hql.Ast.HqlBitwiseOr' to type 'NHibernate.Hql.Ast.HqlBooleanExpression' 例外情况。