'包含（）'解决方法使用Linq到实体？
我试图创建一个使用Silverlight ADO.Net数据服务客户端API（因此Linq To Entities）在where子句中使用id列表的查询。 有谁知道解决方法包含不被支持？
我想要做这样的事情：
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;
但是得到了“方法'Any'不被支持”。
更新： EF≥4直接支持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"
);
}
}
你可以重新编写一些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);
}
并且查询变成：
var query2 = context.Entities.Where(BuildContainsExpression<Entity, int>(e => e.ID, ids));