c# - Linq - 将每个类(class)分组

Question

我需要帮助从电子邮件地址列表中删除重复项。我需要添加代码以在电子邮件地址类中对电子邮件地址进行分组。由于电话号码不同，Sql 返回重复的电子邮件地址。有什么建议么？谢谢。

这是我的代码:<强>1。类

public class Student
{
    public string StudentId { get; set; }
    public string Gender { get; set; }  
    public List<EmailAddresses> emailAddresses { get; set; }
}

public class EmailAddresses
{
    public string EmailAddress { get; set; }    
}

<强>2。来自sql查询的数据

StudentId   EmailAddresses  IsPreferred Number  TelephoneType                                                                                               
123456789   maryjoe@gmail.com   FALSE   5556565 Present Evening Phone                                                                                               
123456789   maryjoe@gmail.com   FALSE   8885566 Permanent Day Phone                                                                                             
123456789   mary.joe@cuu.edu    TRUE    5556565 Present Evening Phone                                                                                               
123456789   mary.joe@cuu.edu    TRUE    8885566 Permanent Day Phone                                                                                             
456789123   dh@mycollege.edu    TRUE    7513150 Business Day Phone                                                                                              
456789123   donna.hill@cu.edu   TRUE    4123300 Present Day Phone                                                                                               
456789123   donna.hill@cu.edu   FALSE   4123300 Present Day Phone

<强>3。代码

public List<Student> GetStudentData()
{
    List<Student> dataStudent;
    using (IDbConnection connection = RepositoryHelper.OpenConnection())
    {
        dataStudent = connection.Query<dynamic>(
            "mystoredprocedure", 
            commandType: CommandType.StoredProcedure)
                .GroupBy(x => x.StudentId)
                .Select(x => new Student 
                    { 
                        StudentId = x.First().StudentId, 
                        Gender = x.First().Gender,
                        emailAddresses = x.Select(ea => new EmailAddresses 
                            { 
                                EmailAddress = ea.emailAddresses 
                            }).ToList()
                    }).ToList();

        return dataStudent;
    }
}

Answer 1

虽然在返回之前过滤掉重复项会更可取，但这也会增加代码的复杂性。如果你的结果集很小，返回数据后过滤的内存和 cpu 开销可能会很容易和清晰地得到你需要的结果。您可以使用自定义 IEqualityComparer 检查不同的结果，并在包含不同电子邮件地址的每个学生记录上创建一个新的 emailAddresses 列表。

public List<Student> GetStudentData()
{
    List<Student> dataStudent;
    using (IDbConnection connection = RepositoryHelper.OpenConnection())
    {
        dataStudent = connection.Query<dynamic>(
            "mystoredprocedure", 
            commandType: CommandType.StoredProcedure)
                .GroupBy(x => x.StudentId)
                .Select(x => new Student 
                    { 
                        StudentId = x.First().StudentId, 
                        Gender = x.First().Gender,
                        emailAddresses = x.Select(ea => new EmailAddresses 
                            { 
                                EmailAddress = ea.emailAddresses 
                            }).ToList()
                    }).ToList();

        dataStudent.ForEach(x => x.emailAddresses = x.emailAddresses
            .Distinct(new StudentEmailEqualityComparer()).ToList());

        return dataStudent;
    }
}

public class StudentEmailEqualityComparer : IEqualityComparer<EmailAddresses>
{

    public bool Equals(EmailAddresses x, EmailAddresses y)
    {
        return x.EmailAddress.Equals(y.EmailAddress);
    }

    public int GetHashCode(EmailAddresses obj)
    {
        return obj.EmailAddress.GetHashCode();
    }
}