如何对此实体框架查询进行改进

Question

我有以下实体：

• 申请人：人
• 电话号码
• PhoneType

申请人来自Person。 Applicant有很多PhoneNumber（最多三个）。每个PhoneNumber只有1个PhoneType。

public class Applicant : Person
{    
    public virtual ICollection<PhoneNumber> PhoneNumbers { get; set; }
}

public class PhoneNumber 
{                        
    public int PersonId { get; set; }

    [Required]
    [MaxLength(17)]
    public string Number { get; set; }    

    public int PhoneTypeId { get; set; }            

    public virtual PhoneType PhoneType { get; set; }

}

public class PhoneType 
{     
    [Required]
    [MaxLength(24)]
    public string Name { get; set; }

    public virtual ICollection<PhoneNumber> PhoneNumbers { get; set; }
}

在我看来，我正在使用的两个查询可以合并，并且可以取消foreach循环，但是我在第一个查询中已经有大量的联接，而且我不确定如何合并它们。问题是一个两部分的问题：

1. 如何合并两个查询和
2. 如果不合并查询，如何改进PhoneNumber / PhoneType查询。

目标是返回带有Applicant列表的PhoneNumber，返回每个带有PhoneNumber的PhoneType。为了清楚起见，类型为：家庭，办公室和手机。

/*------------------------------------------*/
/* Obtain the Applicant                     */
/*------------------------------------------*/
IQueryable<Applicant> applicantQuery = 
      DbContext.Applicants.Where(a => a.CreatedBy == userId)
               .Include(applicant => applicant.Address)
               .Include(applicant => applicant.Address.StateProvince)
               .Include(applicant => applicant.PhoneNumbers)                                                
               .Include(applicant => applicant.HomeChurch)
               .Include(applicant => applicant.HomeChurch.Address)
               .Include(applicant => applicant.HomeChurch.Address.StateProvince)
               .Include(applicant => applicant.TripApplication);

Applicant applicant = applicantQuery.FirstOrDefault<Applicant>();

if (applicant != null && applicant.PhoneNumbers != null)
{
    IQueryable<PhoneType> phoneTypeQuery = DbContext.Set<PhoneType>();
    List<PhoneType> phoneTypes = phoneTypeQuery.ToList<PhoneType>();

    foreach (PhoneNumber ph in applicant.PhoneNumbers)
    {
        ph.PhoneType = (phoneTypes.Where(pt => pt.Id == ph.PhoneTypeId)).First();
    }
}

预先感谢您提供的任何帮助。

Answer 1

EF Core通过将ThenInclude（）]和ThenInclude（）组合在一起来支持加载多个级别，更多信息here

将电话和电话类型一起装扮，您的查询应如下所示（为了清楚起见，我删除了其余的关系）：

var applicant = DbContext.Applicants.Where(a => a.CreatedBy == userId)
        .Include(applicant => applicant.PhoneNumbers)                                                
        .ThenInclude(phone => phone.PhoneType)
        .FirstOrDefault();