Question

我会使用扩展方法翻译此查询我也将使用扩展方法在单个查询中合并此查询

var variants = _ctx.Varianti.Where(i=>i.attivo==0);

var allProducts = await (from p in  _ctx.Articoli
                         where  p.cat==1
                         join v in variants on p.code equals v.code into gj
                         from articoli in gj.DefaultIfEmpty()
                         select new {
                           Codart = p.Codart,
                           Codvar = articoli.Codvar,
                        }).ToListAsync();

我的课程

Articolo类{ 公共字符串Codart // key 公开双重价格 }

瓦里安特级{ 公共字符串Codart // key 公共字符串Codvar //键大众国际 }

我必须像这样退货

Prod1-Variant1 Prod2-（无变体） prod3-Variant1 prod4-Variant1 prod4-Variant2 prod5-（无变体）

我应该仅过滤attivo == 0的变体如果没有的话，所有没有变体的产品

代码运行良好，但我需要在单个查询中对数据库进行优化以及扩展方法

在T-Sql中应该这样：

SELECT Codart,
       Codvar
  FROM dbo.Articoli
       LEFT OUTER JOIN dbo.Varianti
           ON dbo.Articoli.Codart = dbo.Varianti.Codart
 WHERE (Cat = 1)
   AND (attivo = 0)

Answer 1

我仍然不确定是什么问题。这里有一些示例，说明如何“左-外-联接”产品和变体并选择一个新对象。

List<Articolo> products = new List<Articolo>()
{
    new Articolo() { Code = "1", price = 1 },
    new Articolo() { Code = "2", price = 1 },
    new Articolo() { Code = "3", price = 1 },
    new Articolo() { Code = "4", price = 1 },
    new Articolo() { Code = "5", price = 1 },
};

List<Variante> variants = new List<Variante>()
{
    new Variante() { Code = "1", attivo = 0, Codvar = "v1" },
    new Variante() { Code = "3", attivo = 0, Codvar = "v1" },
    new Variante() { Code = "4", attivo = 0, Codvar = "v1" },
    new Variante() { Code = "4", attivo = 0, Codvar = "v2" },
    new Variante() { Code = "5", attivo = 1, Codvar = "v2" },
};

var result = products // Our "Left"-List 
    .GroupJoin( // Join to a "one"-to-"null or many"-List
        variants.Where(v => v.attivo == 0), // Our "right"-List
        p => p.Code, // select key in left list
        v => v.Code, // select key in right list
        (p, v) => // for every product "p" we have a list of variants "v"
            v.Any() ? // do we have vriants for our product?
                v.Select(s =>  new // for every variant we build our new product
                {
                    Code = p.Code,
                    FirstVariant = s.Codvar,
                })
                : // if we got no variants, we build a "no variant"-product
                new[] { new {
                    Code = p.Code,
                    FirstVariant = "No Variant"
                } } // here we got a list of product-variants per product ("list of lists")
            ).SelectMany(s => s); // We want one list of all product variants

foreach (var item in result)
{
    Console.WriteLine("Code: {0}, FirstVar: {1}", item.Code, item.FirstVariant);
}

左外连接扩展方法linq

1 个答案: