c# - 动态+linq编译报错

Question

我会先声明，我正在使用动态数据上的 linq 做一些非常可怕的事情。但是我不明白为什么这个查询编译失败:

错误 1 ​​属性 '<>h__TransparentIdentifier0' 不能与类型参数一起使用

public class Program{    public static void Main(string[] args)    {        var docs = new dynamic[0];        var q = from doc in docs                where doc["@metadata"]["Raven-Entity-Name"] == "Cases"                where doc.AssociatedEntities != null                from entity in doc.AssociatedEntities                where entity.Tags != null // COMPILER ERROR HERE                from tag in entity.Tags                where tag.ReferencedAggregate != null                select new {tag.ReferencedAggregate.Id, doc.__document_id};    }}public static class LinqOnDynamic{    private static IEnumerable<dynamic> Select(this object self)    {        if (self == null)            yield break;        if (self is IEnumerable == false || self is string)            throw new InvalidOperationException("Attempted to enumerate over " + self.GetType().Name);        foreach (var item in ((IEnumerable) self))        {            yield return item;        }    }    public static IEnumerable<dynamic> SelectMany(this object source,                                                    Func<dynamic, int, IEnumerable<dynamic>> collectionSelector,                                                    Func<dynamic, dynamic, dynamic> resultSelector)    {        return Enumerable.SelectMany(Select(source), collectionSelector, resultSelector);    }    public static IEnumerable<dynamic> SelectMany(this object source,                                                    Func<dynamic, IEnumerable<dynamic>> collectionSelector,                                                    Func<dynamic, dynamic, dynamic> resultSelector)    {        return Enumerable.SelectMany(Select(source), collectionSelector, resultSelector);    }    public static IEnumerable<dynamic> SelectMany(this object source,                                                    Func<object, IEnumerable<dynamic>> selector)    {        return Select(source).SelectMany<object, object>(selector);    }    public static IEnumerable<dynamic> SelectMany(this object source,                                                                    Func<object, int, IEnumerable<dynamic>> selector)    {        return Select(source).SelectMany<object, object>(selector);    }}

雪上加霜的是，以下工作:

var docs = new dynamic[0];var q = from doc in docs        where doc["@metadata"]["Raven-Entity-Name"] == "Cases"        where doc.AssociatedEntities != null        from entity in doc.AssociatedEntities        where entity.Tags != null        from tag in entity.Tags        select new { tag.ReferencedAggregate.Id, doc.__document_id };

只有当我添加:

其中 tag.ReferencedAggregate != null

我在两行之前得到一个错误:

where entity.Tags != null//此处编译器错误

不知道发生了什么

Answer 1

如果我尝试将您的调用转换为:

var q = from doc in docs.Where(doc => doc["@metadata"]["Raven-Entity-Name"] == "Cases" || doc.AssociatedEntities != null)
        from entity in doc.AssociatedEntities.Where(entity => entity.Tags != null)

我得到一个不同的编译器错误，它可能揭示了正在发生的事情:

“如果不首先将 lambda 表达式转换为委托(delegate)或表达式树类型，则不能将其用作动态分派(dispatch)操作的参数”

所以我猜你必须重载 Where 运算符。