我只想构建一个动态过滤器。最后返回
Expression<Func<Event, bool>>
我曾尝试使用Combine（AndAlso）表达式，但没有用，最后我发现有一些IQueryable查询效果很好，但是现在我如何将其转换为返回类型-
Expression<Func<Event, bool>>?
我的代码：
public IQueryable<Event> GetBySearch(EventFilter search)
{
IQueryable<Event> query = this.Context.Events.AsQueryable();
Expression<Func<Event, bool>> expression = null;
if (search.CategoryId != 0)
{
query = query.Where(x => x.CategoryId == search.CategoryId);
}
if (search.SubCategoryId != 0)
{
query = query.Where(x => x.SubCategoryId == search.SubCategoryId);
}
expression = query.Expression as Expression<Func<Event, bool>>; //This convert is not working, it returns null.
return this.Context.Events.Where(expression);
}
任何您不只是执行以下操作的原因：
public IQueryable<Event> GetBySearch(EventFilter search)
{
IQueryable<Event> query = this.Context.Events.AsQueryable();
if (search.CategoryId != 0)
{
query = query.Where(x => x.CategoryId == search.CategoryId);
}
if (search.SubCategoryId != 0)
{
query = query.Where(x => x.SubCategoryId == search.SubCategoryId);
}
return query;
}
正如Florian在评论中所说，应避免返回IQueryables（如果可能）。简单的解决方案是返回一个列表：
public List<Event> GetBySearch(EventFilter search)
{
IQueryable<Event> query = this.Context.Events.AsQueryable();
if (search.CategoryId != 0)
{
query = query.Where(x => x.CategoryId == search.CategoryId);
}
if (search.SubCategoryId != 0)
{
query = query.Where(x => x.SubCategoryId == search.SubCategoryId);
}
return query.ToList();
}
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