使用 EF Core 通过中间表访问实体答案

【问题标题】：Access entity through intermediate table with EF Core使用 EF Core 通过中间表访问实体
【发布时间】：2022-11-30 01:48:33
【问题描述】：

我目前正在使用 EF Core，我有 3 个表

Campaign
CampaignStation
Station

CampaignStation是Campaign和Station之间的中间表

活动表：

public class Campaign
{
    public int CampaignId { get; set; }

    public string Name { get; set; } = string.Empty;

    public ICollection<CampaignStation> Stations { get; set; } = new List<CampaignStation>();

 }

public void Configure(EntityTypeBuilder<Campaign> builder)
    {
        builder.HasKey(x => x.CampaignId);
        builder.Property(x => x.Name).IsRequired().HasMaxLength(250);
        builder.HasMany(x => x.Stations).WithOne(y => y.Campaign);
    }

所以一个活动可以有多个站，这就是为什么我有一个中间表作为：

public class CampaignStation
{
    public int CampaignStationId { get; set; }

    public int? CampaignId { get; set; }

    [ForeignKey(nameof(CampaignId))]
    public Campaign? Campaign { get; set; }

    public int? StationId { get; set; }

    [ForeignKey(nameof(StationId))]
    public Station? Station { get; set; }
}


public void Configure(EntityTypeBuilder<CampaignStation> builder)
    {
        builder.ToTable("CampaignStations");
        builder.HasKey(x => x.CampaignStationId);
        builder.HasOne(x => x.Campaign);
        builder.HasOne(x => x.Station);
    }

获取服务：

return await _db.Campaigns
            .Include(a => a.Agency)
            .Include(s => s.Stations)
            .ToListAsync();

但是 Stations 实体总是为 null，它正在获取中间表的 id，如下图所示：

为什么我无法访问 Station Entity？

【问题讨论】：

.Include(s => s.Stations).ThenInclude(cs => cs.Station)。

标签： c# entity-framework asp.net-core entity-framework-core

【解决方案1】：

正如@vernou 的评论，我只需要添加中间表，然后使用ThenInclude 将 Station 表包括在内：

return await _db.Campaigns
            .Include(a => a.Agency)
            .Include(s => s.Stations)
            .ThenInclude(cs => cs.Station)
            .ToListAsync();

【讨论】：