C# LINQ 或 for 循环如何从数据库中获取数据源？答案

【问题标题】：C# LINQ or for loop How to get a data source from a db?C# LINQ 或 for 循环如何从数据库中获取数据源？
【发布时间】：2020-03-16 17:42:22
【问题描述】：

我正在尝试获取列中相同值的每个项目的计数。例如，我有一个包含人员信息的表，我希望它通过名字列并让我计算其中有多少 Joe's 和 Mary's，而无需指定特定名称。

【问题讨论】：

这能回答你的问题吗？ how to use group by in a linq query?
到目前为止你尝试了什么？

标签： c# linq for-loop

【解决方案1】：

您可以按列对数据进行分组

users.GroupBy(x => x.FirstName).Select(x => new
{
    FirstName = x.Key,
    Count = x.Count()
});

【讨论】：

【解决方案2】：

尝试使用GroupBy:

public class People
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    static void Main(string[] args)
    {
        var peoples = new List<People>
        {
            new People { Id = 1, FirstName = "Bob", LastName = "Abc" },
            new People { Id = 2, FirstName = "Joe's", LastName = "Def" },
            new People { Id = 3, FirstName = "Mary's", LastName = "Ghi" },
            new People { Id = 4, FirstName = "Alice", LastName = "Jikl" },
            new People { Id = 5, FirstName = "Bob", LastName = "Mno" },
        };

        var groupedByFirstName = peoples
            .GroupBy(x => x.FirstName)
            .Select(x => new
            {
                FirstName = x.Key,
                Count = x.Count()
            });

        foreach (var people in groupedByFirstName)
        {
            Console.WriteLine($"FirstName: {people.FirstName}. Count: {people.Count}");
        }

        Console.ReadKey();
    }
}

【讨论】：