asp.net-core - Entity Framework Core 始终返回外部行的空列表

Question

我正在使用 Entity Framework Core 和 ASP.NET Core 3.1。

我有两个简单的模型:

public class UserModel 
{
        public int    UserModelId   { get; set; }
        public string Email         { get; set; }
        public string Password      { get; set; }
        public string Name          { get; set; }
        public string Surname       { get; set; }
        public string Token         { get; set; }

        public List<TherapyModel> Therapies { get; set; }
}

public class TherapyModel 
{
        public int      TherapyModelId  { get; set; }
        public int      UserModelId     { get; set; }
        public string   Title           { get; set; }
        public int      Quantity        { get; set; }
        public bool     Monday          { get; set; }
        public bool     Tuesday         { get; set; }
        public bool     Wednesday       { get; set; }
        public bool     Thursday        { get; set; }
        public bool     Friday          { get; set; }
        public bool     Saturday        { get; set; }
        public bool     Sunday          { get; set; }
        public string   ImgBase64       { get; set; }
        public string   ImgUrl          { get; set; }

        public int UserModelForeignKey { get; set; }
        public UserModel UserModel           { get; set; }
}

现在，我用这种方式初始化一切:

public class DatabaseManager : DbContext 
{
        //Entities:
        public DbSet<UserModel>     UserModel    { get; set; }
        public DbSet<TherapyModel>  TherapyModel { get; set; }

        protected override void OnModelCreating( ModelBuilder modelBuilder ) 
        {
            modelBuilder.Entity<TherapyModel>().HasOne(p => p.UserModel)
                                               .WithMany(s => s.Therapies)
                                               .HasForeignKey(p => p.UserModelForeignKey);
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            => optionsBuilder.UseMySql( @"Server=127.0.0.1;database=test2;uid=root;pwd=" ); );
}

本地数据库已使用正确的外键正确填充。事实上这个查询返回 3 行:

select * 
from usermodel 
join therapymodel on therapymodel.UserModelForeignKey 

但是，由于某种原因，当我尝试从 C# 代码获取 UserModel 时，它总是返回“Therapies”为 NULL。我通过这两种方式获取 UserModel :

UserModel user = dbManager.UserModel.FirstOrDefault( user => user.UserModelId == iUserModel.UserModelId );

var users = dbManager.UserModel;

用户和用户的治疗均为 NULL。我实在不明白为什么。有什么帮助吗？

Answer 1

好吧，我终于找到了答案。通过阅读这篇文章:

https://www.learnentityframeworkcore.com/lazy-loading

我启用了延迟加载(默认情况下启用)，但外键必须是虚拟的:

public class Author
{
    public int AuthorId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public virtual List<Book> Books { get; set; } = new List<Book>();
}
public class Book
{
    public int BookId { get; set; }
    public string Title { get; set; }
    public int AuthorId { get; set; }
    public virtual Author Author { get; set; }
}

现在它可以工作了，微软教程没有告诉你任何关于延迟加载和将外键声明为虚拟的事实。我希望这对将来的任何人都有帮助。