c# - 如果 EF Core 5 以多对多关系播种数据

Question

我有用户实体

public class User
{
    public int UserId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public string Password { get; set; }

    public ICollection<Technology> Technologies { get; set; } = new List<Technology>();
}

我有技术实体

public class Technology
{
    public int TechnologyId { get; set; }
    public string TitleTechnology { get; set; }
    public int GroupId { get; set; }
    public Group Group { get; set; }
    public ICollection<User> Users { get; set; } = new List<User>();
}

我想创建多对多关系，所以我有这样的 OnModelCreating方法:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    var groupList = new List<Group>
    {
        new Group {GroupId = 1, TitleGroup = ".NET"}
    };

    var technologyList = new List<Technology>
    {
        new Technology {TechnologyId = 1, GroupId = 1, TitleTechnology = ".NET 5"},
        new Technology {TechnologyId = 2, GroupId = 1, TitleTechnology = ".NET Framework 4.8"},
        new Technology {TechnologyId = 3, GroupId = 1, TitleTechnology = "EF 6"},
        new Technology {TechnologyId = 4, GroupId = 1, TitleTechnology = "ASP.NET MVC 5"}
    };

    var userList = new List<User>
    {
        new User
        {
            UserId = 1, FirstName = "Serhii", LastName = "Yurko", Email = "test", Password = "test",
            Technologies = new List<Technology> {technologyList[0], technologyList[1]}
        }
    };

    modelBuilder.Entity<Technology>().HasOne(exp => exp.Group).WithMany(exp => exp.Technologies).HasForeignKey(exp => exp.GroupId);
    modelBuilder.Entity<User>().HasMany(p => p.Technologies).WithMany(p => p.Users)
        .UsingEntity(j => j.ToTable("UserTechnology"));

    modelBuilder.Entity<User>().HasData(userList);
    modelBuilder.Entity<Group>().HasData(groupList);
    modelBuilder.Entity<Technology>().HasData(technologyList);
    base.OnModelCreating(modelBuilder);
}

当我想创建迁移时，我收到这样的异常 -

The seed entity for entity type 'User' cannot be added because it hasthe navigation 'Technologies' set. To seed relationships, add theentity seed to 'TechnologyUser (Dictionary<string, object>)' andspecify the foreign key values {'UsersUserId'}. Consider using'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see theinvolved property values.

如何建立适当的关系？

Answer 1

在 EF-core 中，您不能直接为导航属性设置种子。您必须删除该行 Technologies = ...来自 User初始化。
如所述 here ，连接表可以通过自己的 HasData 播种通过扩展 UsingEntity() 调用像这样调用:

.UsingEntity(j => j
    .ToTable("UserTechnology")
    .HasData(new[]
        {
            { UsersID = 1, TechnologiesID = 1 },
            { UsersID = 1, TechnologiesID = 2 }
        }
    ));

如您所见，隐藏的连接实体由与表字段具有相同属性名称(+ 类型)的匿名类型填充。这需要您了解这些外键字段的命名约定(我希望我猜对了)。
如 documentation 中所述，您可以通过使用相当笨重的联结表的完全初始化来掌握这一切。和 this Stack Overflow answer .这允许您强制执行自己的 FK 属性名称并在种子代码中相应地使用它们。