c# - 如何进行比嵌套循环更高效的 Entity Framework LINQ 调用

Question

是否有更有效的方式来编写此 LINQ 语句？

功能使用与产品相同的模型(因为它们几乎相同)。

var products = db.Products.Where(q => q.IsFeature == false).ToList();
        foreach (Product pr in products)
        {
            var features = db.Products.Where(q => q.ParentID == pr.ID).ToList();
            foreach(Product feature in features)
            {
                pr.Features.Add(feature);
            }
        }

和模型:

    public class Product
{
    //START
    public Product()
    {
        Features = new HashSet<Product>();
    }

    public int ID { get; set; }
    public string Code { get; set; }
    public string Name { get; set; }
    public bool IsFeature { get; set; }
    public int ParentID { get; set; }// If IsFeature is true we need to know its parent

    //Nav Props
    public ICollection<Product> Features { get; set; }// Features can be represented with the same model as product as they are almost identical
}

这满足了我的需要，即产品列表(Products)，每个产品都有自己的功能列表(Features)，但是否有更优雅/高效的替代方案？

Answer 1

您需要的是 join :

var productFeatures = 
    db.Products.Where(q => !q.IsFeature)
    .Join(db.Products, p => p.ID, f => f.ParentId, (p, f) => new { product: p, features: f.ToList() })
    .ToList();

对于 db.Products.Where(q => !q.IsFeature) 中的每个对象这将找到每个 db.Products有一个 ParentId等于它的 ID字段。

结果将投影到 List() 中具有字段 product (Product) 的匿名类型和 features (List<Product>)