c# - 列表中的 LINQ 查询列表

Question

我有以下 EF 对象列表，Leagues，其中每个对象都有一个 Teams 列表。每个 Team 都有与之关联的年份

在 WPF 表单中，我有一个 combobox 供多年选择。当我选择一年时，我希望能够按当年存在的联赛排序，然后是它拥有的球队，这样我就可以为其填充 TreeView。

到目前为止我最多的是:

    public int SelectedYear
    {
        get => _SelectedYear;
        set
        {
            _SelectedYear = value;
            RaisePropertyChangedEvent("SelectedYear");
            Refresh();
        }
    }

    public void Refresh(object sender = null, EventArgs e = null)
    {
        Leagues = new ObservableCollection<League>(_Locator.Statistix.Leagues.Where(x => x.Teams.Count(t => t.Year == SelectedYear) > 0).ToList());
        foreach(League l in Leagues)
        {
            l.Teams.Where(x => x.Year == SelectedYear);
        }
    }

League对象如下:

public partial class League
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
    public League()
    {
        this.Teams = new HashSet<Team>();
    }

    public int ID { get; set; }
    public string Name { get; set; }
    public string Initials { get; set; }
    public string LahmanID { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<Team> Teams { get; set; }
}

为了更好的衡量，这里还有 Team 对象:

public partial class Team
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
    public Team()
    {
        this.Games = new HashSet<Game>();
        this.Games1 = new HashSet<Game>();
    }

    public int ID { get; set; }
    public int FranchiseID { get; set; }
    public int Year { get; set; }
    public Nullable<int> CityID { get; set; }
    public string Nickname { get; set; }
    public Nullable<int> BallparkID { get; set; }
    public int LeagueID { get; set; }

    public virtual City City { get; set; }
    public virtual Franchise Franchise { get; set; }
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<Game> Games { get; set; }
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<Game> Games1 { get; set; }
    public virtual League League { get; set; }
}

有没有一种方法可以过滤同一个 Leagues ObservableCollection 中球队所关注的联赛？

Answer 1

如果联盟的规模不是太大，我会考虑收集数据，然后提取不需要的数据。

public void Refresh(object sender = null, EventArgs e = null)
    {
        Leagues = new ObservableCollection<League>(_Locator.Statistix.Leagues.ToList());
        foreach(League l in Leagues)
        {
            l.Teams.RemoveAll(x => x.Year == SelectedYear);
        }
        Leagues.RemoveAll(x => x.Teams.Count == 0);
    }

另一种方法是构建 ObserableCollection 固有的专用类并实现 IObseravable 以构建专用逻辑以将类用作 WPF 表单的数据上下文，这将允许系统在选择不同年份时自动过滤.