如何将此 SQL QUERY 转换为 LINQ for Entity Framework

Question

我是 LINQ 的新手，现在正在尝试学习查询的基础知识，由于 Entity Framework，我需要将此 SQL 转换为 LINQ。

SELECT Desktop, Notebook,Gmail, Telefone, Smartphone, Rede, Outros 
FROM Atributos, Gestors, Funcionario, CentroCusto 
WHERE Funcionario.Id = Atributos.Funcionario_Id 
AND Funcionario.CentroCusto_Id = CentroCusto.Id 
AND CentroCusto.Gestor_Id = Gestors.Id 
AND Gestors.Email = 'john@email.com'

Answer 1

这里的另一个问题对此有非常详细的解释：How to do a join in linq to sql with method syntax?

但是，我认为这就是您要寻找的：

from g in Gestors
    join f in Funcionario on g.Id equals f.Gestor_Id 
    join a in Atributos on f.Id equals a.Funcionario_Id
    join c in CentroCusto on f.CentroCusto_Id equals c.Id
where g.Email == "john@email.com"
select new 
{
    //your fields with their tables prefixes
}

对于连接，我喜欢使用这种语法，因为对于刚开始使用 Linq 的人来说，它更易于阅读并且更易于从 SQL 转换。您可以使用 Lambda 语法，但如果您刚刚开始，这将是最容易掌握的，直到您对 Lambda 进行了更多练习。 另外，由于我不知道上述查询中的表结构是什么样的（索引、fk、pk），您可能可以显着提高性能。

Answer 2

实体创建映射到您的数据库的类。下面是获取数据的类和查询示例

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication108
{
    class Program
    {

        static void Main(string[] args)
        {
            string email = "john@email.com";
            DataBase db = new DataBase();
            var results = (from atr in db.Atributos
                           join fun in db.Funcionario on atr.Funcionario_Id equals fun.Id
                           join cen in db.CentroCusto on fun.CentroCusto_Id equals cen.Id
                           join ges in db.Gestors on cen.Gestor_Id equals ges.Id
                           where ges.Email == email
                           select new { desktop = atr.Desktop, notebook = atr.Notebook, gmail = atr.Gmail, tele = atr.Telefone, smartPhone = atr.Smartphone, rede = atr.Rede, outros = atr.Outros })
                           .ToList();
        }

    }
    public class DataBase
    {
        public List<Atributos> Atributos { get; set; }
        public List<Gestors> Gestors { get; set; }
        public List<Funcionario> Funcionario { get; set; }
        public List<CentroCusto> CentroCusto { get; set; }
    }
    public class Atributos
    {
        public string Funcionario_Id { get; set; }

        public string Desktop { get; set; }
        public string Notebook { get; set; }
        public string Gmail { get; set; }
        public string Telefone { get; set; }
        public string Smartphone { get; set; }
        public string Rede { get; set; }
        public string Outros { get; set; }
     }
    public class Gestors
    {
        public string Id { get; set; }
        public string Email { get; set; }
    }
    public class Funcionario
    {
        public string Id { get; set; }
        public string CentroCusto_Id { get; set; }
    }
    public class CentroCusto
    {
        public string Id { get; set; }
        public string Gestor_Id { get; set; }
    }






}