[英]How can I modify this extension method accept two string parameters?
I have the following extension method which behaves like a SQL IN
: 我有以下行为类似于
SQL IN
扩展方法:
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);
}
The problem is that when I call it like this: 问题是当我这样称呼它时:
predicate = predicate.And(x => WhereIn(x.id, Ids));
It gives me an error: The type arguments for method 'WhereIn<TEntity,TValue>(System.Data.Objects.ObjectQuery<TEntity>, System.Linq.Expressions.Expression<System.Func<TEntity,TValue>>, params TValue[])' cannot be inferred from the usage. Try specifying the type arguments explictly.
它给我一个错误:
The type arguments for method 'WhereIn<TEntity,TValue>(System.Data.Objects.ObjectQuery<TEntity>, System.Linq.Expressions.Expression<System.Func<TEntity,TValue>>, params TValue[])' cannot be inferred from the usage. Try specifying the type arguments explictly.
The type arguments for method 'WhereIn<TEntity,TValue>(System.Data.Objects.ObjectQuery<TEntity>, System.Linq.Expressions.Expression<System.Func<TEntity,TValue>>, params TValue[])' cannot be inferred from the usage. Try specifying the type arguments explictly.
x.id is a Ids are both of type string.
I actually don't want to change the method signaure, I would rather change the call to it, but I am not sure what to put in between the brackets of WhereIn<>
. 实际上,我不想更改方法的标志,我希望更改对它的调用,但是我不确定在
WhereIn<>
括号之间放置什么。
I think you're calling the extension method wrong. 我认为您将扩展方法称为错误。
Try like this: 尝试这样:
predicate = predicate.And(x => x.WhereIn(x.id, Ids));
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