EF核心一对多关系列表返回null [英] EF Core One-to-Many relationship list returns null

问题描述

我正在尝试学习如何在EF Core中正确利用DbContext。
我有一个团队课程：

I'm trying to learn how to properly utilize DbContext in EF Core. I have a Team class:

public class Team 
{
    public int ID { get; set; }
    public string Name { get; set; }
    public bool CanSelfManage { get; set; } = false;
    public virtual List<Mileage> Mileages { get; set; }
    public IdentityUser Member { get; set; }
    public string State { get; set; }
    public List<Horse> Horses { get; set; }
}

和里程舱：

public class Mileage
{
    public int ID { get; set; }
    public virtual Team Team { get; set; }
    public virtual int TeamID { get; set; }
    public DateTime Date { get; set; }
    public LogType Type { get; set; }
    public decimal Miles { get; set; }
    public IdentityUser User { get; set; }
    public List<Horse> Horses { get; set; }
}

我的DbContext类包含

And my DbContext class contains

public DbSet<Team> Teams { get; set; }
public DbSet<Mileage> Mileages { get; set; }
public DbSet<Horse> Horses { get; set; }
public DbSet<SecurityEntry> SecurityEntries { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);
    modelBuilder.Entity<Mileage>()
        .HasOne(t => t.Team)
        .WithMany(b => b.Mileages)
        .HasForeignKey(t => t.TeamID)
        .IsRequired();
    modelBuilder.Entity<Horse>()
        .HasOne(t => t.Team)
        .WithMany(h => h.Horses);
    modelBuilder.Entity<Horse>()
        .HasMany(m => m.Mileages);
    modelBuilder.Entity<Mileage>()
        .HasMany(h => h.Horses);
}

我遇到的问题是，无论我做什么， Team.Mileages返回null，并且从不填充。

如果将列表设置为不被映射，则注入DbContext并尝试从上下文中运行任何内容，它会引发以下错误：

The problem that I'm having is that, no matter what I do, Team.Mileages returns null and is never populated.
If I set the List to not be mapped, inject the DbContext and try to run anything off of the context, it throws the following error:

在此上下文中，在上一个操作
完成之前第二次操作开始

A second operation started on this context before a previous operation completed

我想念的明显的东西？我正在使用MySQL，如果有任何不同的话。

Is there something glaring that I'm missing? I am using MySQL, if that makes any difference.

推荐答案

默认情况下，实体框架使用惰性加载，您可以设置为渴望加载并始终加载引用，也可以要求收集根据数据库请求。
示例：

Entity framework by default uses Lazy loading, you either set to eager loading and load your references always or you ask for your collections on a database request. Example:

_dbcontext.Team.Include(team => team.Mileages).ToList();

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