EFCoreFirstEagerLoading繼承過濾器-有解無憂

我定義了以下物體：

public class Computer
{
    [Key]
    public int Id { get; set; }

    [Required]
    [StringLength(15)]
    public string Name { get; set; } = null!;

    [Required]
    public List<ComputerAction> Actions { get; set; } = new();
}

public abstract class ComputerAction
{
    [Key]
    public int Id { get; set; }

    public List<HistoryEntry> History { get; set; } = new();

    public Computer Computer { get; set; } = null!;

    [NotMapped]
    public Status Status => History.LastOrDefault()?.Status ?? Status.Unknown;

    public abstract Task<HistoryEntry> ExecuteAsync();
}

public class RenewCertificateAction : ComputerAction
{
    public override Task<HistoryEntry> ExecuteAsync() 
    {
        // Whatever
    }
}

public class PingAction : ComputerAction
{
    private readonly Ping _ping = new();

    public override async Task<HistoryEntry> ExecuteAsync()
    {
        // Whatever
    }
}

public class HistoryEntry
{
    [Key]
    public int Id { get; set; }

    [Required]
    public Status Status { get; set; }

    [Required]
    public DateTime WhenExecuted { get; set; }
}

我的 DbContext 如下：

public class ComputerContext : DbContext
{
    public ComputerContext(DbContextOptions<ComputerContext> options)
        : base(options)
    {
    }

    public static readonly string ComputerDb = nameof(ComputerDb);

    public DbSet<Computer> Computers { get; set; } = null!;

    public DbSet<RenewCertificateAction> RenewCertificateActions { get; set; } = null!;

    public DbSet<PingAction> PingActions { get; set; } = null!;

    public DbSet<HistoryEntry> History { get; set; } = null!;

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Computer>().HasMany(x => x.Actions).WithOne(x => x.Computer).OnDelete(DeleteBehavior.Cascade);
        modelBuilder.Entity<ComputerAction>().ToTable("ComputerActions").HasMany(x => x.History).WithOne().OnDelete(DeleteBehavior.Cascade);
        modelBuilder.Entity<HistoryEntry>().ToTable("ComputerActionEntries");
    }
}

我想獲取所有計算機的串列，但如果它們碰巧有一個 type 的動作PingAction，那么還要加載那個動作（并且只有那個動作，而不是所有動作）。

對我來說合乎邏輯的是，dbContext.Computers.Include(x => x.Actions.OfType<PingAction>())但顯然不能轉化為查詢。我怎樣才能Include只做Actions一個特定型別的？

uj5u.com熱心網友回復：

你可以使用 where 里面包括：

dbContext.Computers.Include(x => x.Actions.Where(action => action is PingAction))

更多解釋：： https ://stackoverflow.com/a/61147681/11143288

轉載請註明出處，本文鏈接：https://www.uj5u.com/houduan/426626.html

標籤：C＃。网实体框架

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