LINQ到实体铸造问题 [英] LINQ-to-entities casting issue

问题描述

我试图以通用方式过滤LINQ到实体查询，但我不断收到错误。这里是一段代码：

I'm trying to filter a LINQ-to-entities query in a generic way, but I keep getting an error. Here is a piece of code:

private IQueryable<T> FilterDeletedEntities<T>(IQueryable<T> entities)
{
    if (typeof(IDeletable).IsAssignableFrom(typeof(T)))
    {
        var deletableEntities = (IQueryable<IDeletable>)entities;
        deletableEntities = deletableEntities.Where(entity => !entity.Deleted);
        entities = (IQueryable<T>)deletableEntities;
    }
    return entities;
}

基本上我试图过滤掉被删除的实体是'true'），当且仅当实体是IDeletable（即它有'Deleted'字段）。问题是，我不能铸造IQueryable< IDeletable>返回IQueryable< T>。

Basically I'm trying to filter out deleted entities (i.e. 'Deleted' field is 'true'), if and only if the entity is IDeletable (i.e. it has the 'Deleted' field). The problem is that I can't cast IQueryable< IDeletable > back to IQueryable< T >.

有关如何解决这个问题的任何想法？

Any ideas on how to fix this? And before you ask: yes, this method has to be generic.

提前感谢！

I was able to solve my problem by doing this:

private IQueryable< T> FilterDeletedEntities< T>（IQueryable实体）
{
if（typeof（IDeletable）.IsAssignableFrom（typeof（T）））
{
var deletableEntities =（IQueryable& IDeletable>）实体;
return deletableEntities.Where（entity =>！entity.Deleted）.Cast< T>（）;
}
返回实体;
}

private IQueryable<T> FilterDeletedEntities<T>(IQueryable<T> entities) { if (typeof(IDeletable).IsAssignableFrom(typeof(T))) { var deletableEntities = (IQueryable<IDeletable>)entities; return deletableEntities.Where(entity => !entity.Deleted).Cast<T>(); } return entities; }

感谢tvanfosson的灵感。

Thanks to tvanfosson for the inspiration.

这篇关于LINQ到实体铸造问题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！