Question

我已按照Issue #1368和Docs Here中描述的多对多解决方法的说明进行操作...但是当我尝试导航时，它始终返回null。

我的模特：

    public class Organization
{
    public Guid OrganizationID { get; set; }

    //...

    public ICollection<OrganizationSubscriptionPlan> OrganizationSubscriptionPlans { get; set; }

}

public class SubscriptionPlan
{
    public int SubscriptionPlanID { get; set; }

    //...

    public ICollection<OrganizationSubscriptionPlan> OrganizationSubscriptionPlans { get; set; }


public class OrganizationSubscriptionPlan
{
    [ForeignKey("Organization")]
    public Guid OrganizationID { get; set; }
    public Organization Organization { get; set; }

    [ForeignKey("SubscriptionPlan")]
    public int SubscriptionPlanID { get; set; }
    public SubscriptionPlan SubscriptionPlan { get; set; }
}

ApplicationDbContext：

    protected override void OnModelCreating(ModelBuilder builder)
{
    base.OnModelCreating(builder);
    builder.Entity<OrganizationSubscriptionPlan>().HasKey(x => new { x.OrganizationID, x.SubscriptionPlanID });
    builder.Entity<OrganizationSubscriptionPlan>().HasOne(x => x.Organization).WithMany(x => x.OrganizationSubscriptionPlans).HasForeignKey(x => x.OrganizationID);
    builder.Entity<OrganizationSubscriptionPlan>().HasOne(x => x.SubscriptionPlan).WithMany(x => x.OrganizationSubscriptionPlans).HasForeignKey(x => x.SubscriptionPlanID);
}

我的查询：

var organizations = _context.Organizations
    .Include(o => o.OrganizationSubscriptionPlans);

foreach (var organization in organizations)
{
    //....
    var subscriptions = organization.OrganizationSubscriptionPlans
            .Select(s => s.SubscriptionPlan);
     // ^^^^^^^^^^^ why is subscriptions always null?
}

＆＃34;组织＆＃34; query按预期返回结果，包括每个中的OrganizationSubscriptionPlans列表，但是当我尝试在foreach循环中导航到它们时，＆＃34; subscriptions＆＃34;查询每次都返回null。我做错了什么？

Answer 1

原来这是一个延迟加载问题。您必须“包含”加入实体，然后“ThenInclude”另一个实体。

var organizations = _context.Organizations
    .Include(o => o.OrganizationSubscriptionPlans)
    .ThenInclude(s => s.SubscriptionPlan);

Answer 2

ForeignKey attr用于修饰引用属性以指示它们保存FK值的原始属性。

public class OrganizationSubscriptionPlan
{    
    public Guid OrganizationID { get; set; }
    [ForeignKey("OrganizationID")]
    public Organization Organization { get; set; }

    public int SubscriptionPlanID { get; set; }
    [ForeignKey("SubscriptionPlanID")]
    public SubscriptionPlan SubscriptionPlan { get; set; }
}

实体框架核心（EF 7）多对多结果始终为空

2 个答案: