[英]LINQ query using TPH inheritance - get derived class ICollection count
我試圖弄清楚如何獲取特定ProjectDoc.OfType上ProjectSummaryVotes的計數。 該查詢有效,但ProjectSummaryVote屬性為null,這意味着出現空值錯誤。 這可行嗎? 如果需要,我應該放棄TPH繼承嗎?
模型:
public class Project
{
public int ProjectID { get; set; }
public virtual ICollection<ProjectDoc> ProjectDoc { get; set; }
}
public abstract class ProjectDoc
{
public int ProjectDocID { get; set; }
public int ProjectID { get; set; }
public string DocTitle { get; set; }
public string Status { get; set; }
public DateTime DateCreated { get; set; }
public virtual Project Project { get; set; }
public virtual ICollection<Comment> Comment { get; set; }
}
public class Summary : ProjectDoc
{
[DataType(DataType.MultilineText)]
public string Text { get; set; }
public ICollection<ProjectSummaryVote> ProjectSummaryVote { get; set; }
}
public class ProjectSummaryVote
{
public int ProjectSummaryVoteID { get; set; }
public int ProjectDocID { get; set; }
public bool Vote { get; set; }
public virtual Summary Summary { get; set; }
public virtual User User { get; set; }
}
查詢:
Project project = db.Projects
.Include(i => i.User)
.Include(i => i.ProjectDoc)
.SingleOrDefault(x => x.ProjectID == id);
嘗試獲取引發錯誤的計數。
var trueCount = Model.ProjectDoc.OfType<Literrater.Models.Summary>()
.Where(s => s.Status == "Active")
.SelectMany(v => v.ProjectSummaryVote.Where(s => s.Vote == true))
.Count();
我對數據進行了重新建模,以便所有投票現在都成為單個投票模型的一部分。 這樣一來,我就可以將投票關系從派生模型移到主要模型中,從而可以輕松訪問數據。
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