实际上，我有一个问题，即我不能为可空字段设置空值而不是默认值。
我无法在 select 语句中使用 EF core 2.1 编写正确的代码，因为我遇到了运行时异常“值不能为空”或者无法使用空传播运算符。
注意：如果重要，则从查询中的子实体获取行。
VotedAt = i.CurrentUserVote == null
? new DateTimeOffset()
: i.CurrentUserVote.VotedAt,
CurrentUserVote = i.CurrentUserVote == null
? false
: i.CurrentUserVote.IsPositive,
我想写：
VotedAt = i.CurrentUserVote == null
? null
: i.CurrentUserVote.VotedAt,
CurrentUserVote = i.CurrentUserVote == null
? null
: i.CurrentUserVote.IsPositive,
甚至：
VotedAt = i.CurrentUserVote?.VotedAt,
CurrentUserVote = i.CurrentUserVote?.IsPositive,
社区要求的其他信息： 选定的实体：
public class IssueListItem
{
public int Id { get; set; }
public string Title { get; set; }
public Votes Votes { get; set; }
}
public class Votes
{
public int Positive { get; set; }
public int Negative { get; set; }
public int All { get; set; }
public bool? CurrentUserVote { get; set; }
public DateTimeOffset? VotedAt { get; set; }
}
选择：
return _unitOfWork.Issues.GetQuery()
.Filter(query.Filter)
.WithVotes<Issue, IssueVote, int>(currentUserId)
.Order(query.Sorter)
.Select(i => new IssueListItem
{
Id = i.Item.Id,
Votes = i.Votes,
Title = i.Item.Title,
//removed some other properties
})
.ToListAsync();
哪里WithVotes<Issue, IssueVote, int>(currentUserId)是：
return q
.Select(i => new
{
Item = i,
VoutesGroups = i.Votes
.GroupBy(v => v.IsPositive, v => true, (key, vg) => new { IsPositive = key, Count = vg.Count() }),
CurrentUserVote = currentUserId == null ? null : i.Votes.FirstOrDefault(v => v.CreatedById == currentUserId),
})
.Select(i => new AssignVotesModel<TEntity, TVote, TId>
{
Item = i.Item,
Votes = new Votes
{
Positive = i.VoutesGroups.Where(vg => vg.IsPositive == true).Sum(vg => vg.Count),
Negative = i.VoutesGroups.Where(vg => vg.IsPositive == false).Sum(vg => vg.Count),
All = i.VoutesGroups.Sum(vg => vg.Count),
VotedAt = i.CurrentUserVote == null ? new DateTimeOffset() : i.CurrentUserVote.VotedAt,
CurrentUserVote = i.CurrentUserVote == null ? false : i.CurrentUserVote.IsPositive,
}
});