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Accepted
zergon321
Asked:2020-03-27 02:24:19 +0000 UTC2020-03-27 02:24:19 +0000 UTC

在 LINQ 中按 2 个字段分组

  • 772

有 2 个数据集 - 宠物：

Pet[] pets =
        {
            new Pet() { Name = "Vasya", Type = "Cat", Owner = "John" },
            new Pet() { Name = "Borya", Type = "Dog", Owner = "Dean" },
            new Pet() { Name = "Kim", Type = "Hedgehog", Owner = "Mary" },
            new Pet() { Name = "Joka", Type = "Dog", Owner = "John" },
            new Pet() { Name = "Mursick", Type = "Cat", Owner = "Dean" },
            new Pet() { Name = "Mick", Type = "Cat", Owner = "Mary" },
            new Pet() { Name = "John", Type = "Hedgehog", Owner = "John" },
            new Pet() { Name = "Jynx", Type = "Dog", Owner = "Dean" }
        };

和他们的主人：

Owner[] owners =
        {
            new Owner() { Name = "John", Country = "USA" },
            new Owner() { Name = "Mary", Country = "Switzerland" },
            new Owner() { Name = "Dean", Country = "Great Britain" }
        };

从这两组中，我想确定每个国家有多少每种类型的宠物。那些。我需要一个与此SQL查询等效的LINQ查询：

SELECT O.Country, P.Type, Count(P.Type) AS Amount
FROM owners AS O INNER JOIN pets AS P
ON O.Name = P.Owner
GROUP BY O.Country, P.Type;

有可能用LINQ得到这个吗？

c#

2 个回答

  1. Best Answer

    这样的表情来了

    var el = from o in owners
         join p in pets
         on o.Name equals p.Owner
         group p by new {o.Country, p.Type}
         into grp 
             select new { 
                          Country = grp.Key.Country, 
                          Type = grp.Key.Type, 
                          Count = grp.Count() 
                        };

    在这里测试 - https://ideone.com/agkzWZ

    • 2

  2. 像这样的东西

     var result = owners.Join(pets, o => o.Name, p => p.Owner, (o,p) => new{o,p})
            .GroupBy(j => new { j.o.Country, j.p.Type})
            .Select(g => new {g.Key.Country, g.Key.Type, Amount = g.Count(), });
    • 2

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