小编Al_*_*l_B的帖子

我正在尝试评估Angular 2,我遇到了observables的问题.

我试图创建一个简单的服务,最初返回硬编码数组,但最终将从Web服务获取数据.

但是,我无法让它构建好.

有任何想法吗？

export class FleetListService {

  private data: Observable<Array<IFleet>>;

  constructor() { }

  fleets: IFleet[] = JSON.parse( `[{ "id": 1, "name": "John", "description": "John has been in the Audio/Video industry since 1990. He has led DevAv as its CEO since 2003. When not working hard as the CEO, John loves to golf and bowl. He once bowled a perfect game of 300.", "childCount": 5, "isUsed": true }, 
                                   { "id": 2, "name": "Olivia", "description": "Olivia loves to sell. She …

我一直在尝试使用 GroupJoin 语句对两个表进行左外连接，以便我可以获得表 A 中的行列表，而表 B 中没有任何项目。但是我不断收到异常

  Exception found: Processing of the LINQ expression 'DbSet<People>
      .GroupJoin(
          outer: DbSet<RiskGroup>,
          inner: person => (Nullable<int>)person.Id,
          outerKeySelector: risk => risk.AssessorId,
          innerKeySelector: (person, risks) => new {
              person = person,
              risks = risks
                  .DefaultIfEmpty()
           })' by 'NavigationExpandingExpressionVisitor' failed. 

这似乎意味着在 EF Core v3 中这是不可能的。有谁知道如何解决这个问题，或者我的 LINQ 是否不正确：

    var Ids = destContext.People.GroupJoin(destContext.RiskGroup,
        person => person.Id,
        risk => risk.AssessorId,
        (person, risks) => new { person, risks = risks.DefaultIfEmpty() }).ToList();

我试图找到 person 表中在 RiskGroup 表中没有行的所有行。