MVC tracking fields such as Author and Editor (Created By and Modified By)

问题

I'm looking for the best way to track the Author and Editor fields for all the entities in my database.

I started by creating a base model which all my models inherit from:

public class DatabaseEntity
{
    [Key]
    public int Id { get; set; }

    [Display(Name = "Last Modified By")]
    public ApplicationUser Editor { get; set; }

    [DisplayFormat(ApplyFormatInEditMode = true, DataFormatString = "{0:MM/dd/yyyy}")]
    [Display(Name = "Last Modified")]
    public DateTime LastModified { get; set; }

    [Display(Name = "Created By")]
    public ApplicationUser Creator { get; set; }

    [DisplayFormat(ApplyFormatInEditMode = true, DataFormatString = "{0:MM/dd/yyyy}")]
    public DateTime Created { get; set; }
}

This works good, but I have to set these fields in every action in my controllers. How can I set these fields every time an item in my database is updated or edited? I am aware that I could override Add in my DbContext, but I have no idea how to get the ApplicationUser from the HttpContext.Current.User.Identity in my DbContext. I have tried:

public class ApplicationDbContext : IdentityDbContext<ApplicationUser> {
    private readonly UserManager<ApplicationUser> userManager;
    private readonly HttpContext httpContext;

    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options, UserManager<ApplicationUser> userManager, IHttpContextAccessor contextAccessor)
    : base(options)
    {
        this.contextAccessor = contextAccessor;
        this.httpContext = contextAccessor.HttpContext;
        this.userManager = userManager;
    }

    public override EntityEntry<TEntity> Add<TEntity>(TEntity entity)
    {
        DatabaseEntity dbEntity = (entity as DatabaseEntity);
        if (dbEntity != null)
        {
            dbEntity.Created = DateTime.Now;
            dbEntity.Creator = await userManager.GetUserAsync(httpContext.User);
        }

        return base.Add(entity);
    }
}

but this gives error because userManager.GetUserAsync(httpContext.User); requires an await and public override EntityEntry<TEntity> Add<TEntity>(TEntity entity) is not async.

回答1:

For getting current user, you should not use UserManager<ApplicationUser>. With commenting dbEntity.Creator = await userManager.GetUserAsync(httpContext.User);, you will get error A circular dependency was detected for the service of type 'CoreDb.Data.ApplicationDbContext'. due to that you accessing UserManager<ApplicationUser> in ApplicationDbContext.

I suggest you try get the current user by querying DbSet<ApplicationUser> with current user name.

Here is a simple code:

    public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{       
    private readonly HttpContext httpContext;

    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options, IHttpContextAccessor contextAccessor)
        : base(options)
    {
        this.httpContext = contextAccessor.HttpContext;
    }       
    public DbSet<ApplicationUser> ApplicationUser { get; set; }
    public override EntityEntry<TEntity> Add<TEntity>(TEntity entity)
    {
        DatabaseEntity dbEntity = (entity as DatabaseEntity);
        var userName = httpContext.User.Identity.Name;
        if (dbEntity != null)
        {
            dbEntity.Created = DateTime.Now;
            dbEntity.Creator = userName == null ? null : ApplicationUser.Where(user => user.UserName == userName).FirstOrDefault();
        }
        return base.Add(entity);    
    }
    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);            
    }        
}

来源：https://stackoverflow.com/questions/49142880/mvc-tracking-fields-such-as-author-and-editor-created-by-and-modified-by