Linq查询与聚合

Question

我想编写一个优雅的linq查询来处理以下SAMPLE对象模型:

    class Category
    {
        public string Name { get; set; }        
        public IList<Product> Products { get; set;}        
    }

    class Product
    {
        public string Title { get; set; }
        public IList<Photo> Photos { get; set; }
    }

    class Photo
    {
        public int Id { get; set; }
    }

我构造了以下查询来获取照片ID:

    var query = from category in Factory.GetCategories()
                where category.Name == "Cameras"
                select (from product in category.Products
                        where product.Title == "Sony"
                        select (from photo in product.Photos
                                select photo.Id)
                               );

    var v = query.ToList();

在查询没有正确投影的那一刻,我必须为每个Sub Selects添加FirstOrDefault()!:

var query = from category in Factory.GetCategories()
                where category.Name == "Cameras"
                select (from product in category.Products
                        where product.Title == "Sony"
                        select (from photo in product.Photos
                                select photo.Id).FirstOrDefault()
                               ).FirstOrDefault();

var v = query.ToList();

有一个更好的方法吗？忽略我们没有处理数据库和PK/FK的事实并没有发挥作用.

当我在linq查询中做同样的事情时,我真的想避免编写一个大的for循环:

foreach (var category in Factory.GetCategories())
            {
                if (category.Name == "Camera")
                {
                    foreach (var product in category.Products)
                    {
                        if (product.Title == "Sony")
                        {
                            foreach (var photo in product.Photos)
                            {
                                //get data
                                int id = photo.Id;
                            }
                        }
                    }
                }                
            }

实际的实现比这个简单的对象模型更复杂.我想从这个简单的样本中得到基本的想法,所以我将它应用到我的真实对象模型.

干杯!

Answer 1

你只想要扁平的ids吗？

        var query = from category in Factory.GetCategories()
                    where category.Name == "Cameras"
                    from product in category.Products
                    where product.Title == "Sony"
                    from photo in product.Photos
                    select photo.Id;