System.InvalidOperationException：可为 Null 的对象必须在实体框架查询中具有值

Question

我有两个与数据库实体相关的实体。我已经像这样设置了模型以及我的

ApplicationDbContext

。但是，当我尝试对其运行查询以从相关实体获取数据时，我收到此错误。

System.InvalidOperationException：可为 Null 的对象必须有一个值。`

我怎样才能让它发挥作用？

查询

var fixtures = await _context.Fixtures
    .Where(i => i.HomeTeam.Id == seasonteamid || i.AwayTeam.Id == seasonteamid)
    .Select(i => new Match
    {
        ReferenceId = i.Id,
        MatchType = MatchType.League,
        DateTime = i.SeasonCalendarDate.Date,
        DateName = i.SeasonCalendarDate.Name,
        MatchDetails = i.Division.Name,
        HomeTeamName = i.HomeTeam.TeamName,
        AwayTeamName = i.AwayTeam.TeamName,
        HomeTeamId = i.HomeTeam.Id,
        AwayTeamId = i.AwayTeam.Id,
        HomeFrameScore = i.Result.HomeScore,
        AwayFrameScore = i.Result.AwayScore,
        MatchStatus = i.MatchStatus,
        LeagueId = i.League.Id
    }).ToListAsync();

夹具.cs

public class Fixture
{
    public long Id { get; set; }
    public DateTime Date { get; set; }
    public League League { get; set; }
    public Season Season { get; set; }
    public Result Result { get; set; }
    //Properties omitted for brevity
}

结果.cs

public class Result
{
    public long Id { get; set; }
    public League League { get; set; }
    public SeasonDivision Division { get; set; }
    public SeasonCalendarDate SeasonCalendarDate { get; set; }
    public Fixture Fixture { get; set; }
    //Properties omotted for brevity
}

ApplicationDbContext.cs

builder.Entity<Result>()
    .HasOne(i => i.Fixture)
    .WithOne(a => a.Result)
    .HasForeignKey<Fixture>(c => c.Id);

Answer 1

您的问题似乎不是加载导航属性，因为您在选择部分中使用了它们并且它们的值为 Null，您面临此错误

            var fixtures = await db.Fixtures
                         .Include(r => r.Result)
                         .Include(r => r.SeasonCalendarDate)
                         .Include(r => r.Division)
                         .Include(r => r.HomeTeam)
                         .Include(r => r.AwayTeam)
                         .Select(i => new
                         {
                             ReferenceId = i.Id,
                             MatchType = MatchType.League,
                             DateTime = i.SeasonCalendarDate.Date,
                             DateName = i.SeasonCalendarDate.Name,
                             MatchDetails = i.Division.Name,
                             HomeTeamName = i.HomeTeam.TeamName,
                             AwayTeamName = i.AwayTeam.TeamName,
                             HomeTeamId = i.HomeTeam.Id,
                             AwayTeamId = i.AwayTeam.Id,
                             HomeFrameScore = i.Result.HomeScore,
                             AwayFrameScore = i.Result.AwayScore,
                             MatchStatus = i.MatchStatus,

                         }).ToListAsync();;