EF扩展方法:"此功能只能从LINQ援引实体"。 [英] EF extension method: "This function can only be invoked from LINQ to Entities."
问题描述
我做了一个扩展的方法来EF实体:
公共静态的IEnumerable< T> WildcardSearch< T>(这个IEnumerable的< T>的实体,
字符串参数,函数功能< T,
弦>选择器)
{
返回entity.Where(L => SqlFunctions .PatIndex(参数,选择器(1))大于0);
}
//例外:此功能只能从LINQ援引实体。
结果= context.FOO.WildcardSearch(ID,X => x.Id).ToList();
我得到上面的异常,如果我尝试使用它。
不过,如果我在我的收藏中运行(我认为)非常相同的代码直接,它可以作为intented。
为什么我的例外,是有什么办法可以解决这个问题?
相似的主题建议改变类型的IQueryable
,但它似乎并没有帮助。
//这个作品
结果= context.FOO.Where(X => ;
SqlFunctions.PatIndex(ID,x.Id)大于0).ToList();
它需要的IQueryable< ; T>
和表达式来; Func键< ...>>
;不幸的是,这意味着重建的表达式树 - 例如:
公共静态的IQueryable< T> WildcardSearch< T>(这IQueryable的< T>的实体,
字符串参数,表达式来; Func键< T,串>>选择器)
{
变种的λ= Expression.Lambda< Func键<吨,布尔>>(
Expression.GreaterThan(
Expression.Call(
typeof运算(SqlFunctions),PATINDEX,空,
Expression.Constant(参数中的typeof(串)),
selector.Body)
Expression.Constant(0)),
selector.Parameters);
返回entity.Where(拉姆达);
}
I have made an extension method to EF entities:
public static IEnumerable<T> WildcardSearch<T>(this IEnumerable<T> entity,
string param, Func<T,
string> selector)
{
return entity.Where(l => SqlFunctions.PatIndex(param, selector(l)) > 0);
}
//exception: This function can only be invoked from LINQ to Entities.
result = context.FOO.WildcardSearch(id, x => x.Id).ToList();
I get the exception above if I try to use it.
However, if I run (what I assume) the very same code directly on my collection, it works as intented.
Why do I get the exception, and is there any way to fix this?
Similar threads suggest changing the type to IQueryable
, but it doesn't seem to help.
//this works
result = context.FOO.Where(x =>
SqlFunctions.PatIndex(id, x.Id) > 0).ToList();
It needs to be IQueryable<T>
and Expression<Func<...>>
; unfortunately this means rebuilding the expression tree - for example:
public static IQueryable<T> WildcardSearch<T>(this IQueryable<T> entity,
string param, Expression<Func<T, string>> selector)
{
var lambda = Expression.Lambda<Func<T, bool>>(
Expression.GreaterThan(
Expression.Call(
typeof(SqlFunctions), "PatIndex", null,
Expression.Constant(param, typeof(string)),
selector.Body),
Expression.Constant(0)),
selector.Parameters);
return entity.Where(lambda);
}
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