将项目添加到 EF Core 中的集合导航属性

Question

我有一个 Project 类，其中包含 AppUsers 的集合

public class Project
{
    public int ProjectID { get; set; }

    [Required(ErrorMessage = " Please enter a project name")]
    public string Name { get; set; }

    [Required(ErrorMessage = " Please enter a project description")]
    public string Description { get; set; }

    public virtual ICollection<AppUser> ProjectManagers { get; set; }

    public bool UserIsAlreadyPM(string userId)
    {
        foreach(AppUser user in this.ProjectManagers)
        {
            if(user.Id == userId)
            {
                return true;
            }
        }
        return false;
    }
}

我的AppUser 班级

public class AppUser : IdentityUser
{
    //add properties here later
}

我希望能够让任何特定的AppUser 位于多个Project 的ProjectManagers 内。我通过我的存储库方法将AppUser 添加到任何Project.ProjectManagers：

public void AddProjectManager(int projectID, AppUser user)
{
      Project proj = context.Projects.FirstOrDefault(p => p.ProjectID == projectID);
      if(proj != null)
      {
          proj.ProjectManagers.Add(user);
          context.SaveChanges();
      }
}

这在AppUser 首次添加到Project.ProjectManagers 集合时有效。但是，如果我尝试将它们添加到任何其他 Project.ProjectManagers 集合中，这将不起作用。如果将它们分配给任何后续的Project.ProjectManagers，我会收到主键错误，因为它们已经在不同项目下的数据库中。

“SqlException：违反PRIMARY KEY约束'PK_AppUser'。无法在对象'dbo.AppUser'中插入重复键。重复键值为（xxxx）。”

Answer 1

请按如下方式编写代码：

public void AddProjectManager(int projectID, AppUser user)
{
        Project proj = context.Projects.Include(p => p.ProjectManagers)
                              .FirstOrDefault(p => p.ProjectID == projectID);

        if(!proj.ProjectManagers.Any(pm => pm.Id = user.Id)) // <-- Here check that `AppUser` already not in Project's `ProjectManagers` collection
        {
            AppUser appUser =  context.AppUsers.FirstOrDefault(p => p.Id== user.Id);
            if(appUser != null) // <-- Confirm that the `AppUser` you are trying to add to Project's `ProjectManagers` collection is already exist in database
            {
                proj.ProjectManagers.Add(appUser);
                context.SaveChanges();
            }
        }
 }