实体框架-用TPT设置加载子类实体

Question

我们的系统正在接收来自两个外部来源的输入(电话/网络提交)。

//  Table-Per-Type Hierarchy
public class Submission
{
    public int SubmissionId { get; set; }   // Primary Key
    public int? PersonId { get; set; }
    public int? CompanyId { get; set; }
    public long? EmployeeId { get; set; }
    public bool? Completed { get; set; }
    public string AbsenceReason { get; set; }
    public string AbsenceType { get; set; }
    public DateTime? AbsenceDate { get; set; }
}

public class CallSubmission : Submission
{
    public string CallerId { get; set; }
    public string PhoneNumber { get; set; }
    public DateTime? HangUp { get; set; }
    public DateTime? PickUp { get; set; }        
}

public class WebSubmission : Submission
{
    public string EmailAddress { get; set; }
    public string PhoneNumber { get; set; }
    public DateTime SubmissionDate { get; set; }
}

我的目标是检索所有提交在过去七天内使用皮卡/SubmissionDate，取决于提交的类型，我们正在处理。是否有可能通过一个LINQ语句来实现这一点？理想情况下，我希望避免在内存中加载两个不同的数据集。

语句--我希望集成

Users.Where(user => user.UserName == name)
     .SelectMany(user => user.Submissions)
     .OfType<CallSubmission)()
     .Where(call => call.PickUp >= startDate)

Users.Where(user => user.UserName == name)
     .SelectMany(user => user.Submissions)
     .OfType<WebSubmission>()
     .Where(web => web.SubmissionDate >= startDate)

Answer 1

实际上(对我来说令人惊讶)，您问的是什么是可能的(至少在最新的EF6.1.3中)，因为支持C# is和as运算符(基本上由OfType方法使用)。

var query = db.Users
    .Where(user => user.UserName == name)
    .SelectMany(user => user.Submissions)
    .Where(subm => (subm as CallSubmission).PickUp >= startDate
        || (subm as WebSubmission).SubmissionDate >= startDate);

重要的部分是使用as操作符而不是生成不受支持的异常的cast。不需要检查null，因为生成的SQL查询自然处理NULL的查询。