Question

如果我有以下实体：

public class PocoWithDates {
    public string PocoName { get; set; }
    public DateTime DateCreated { get; set; }
   public DateTime DateUpdated { get; set; }
}

对应于具有相同名称/属性的SQL Server 2008（R2）表...

我该如何自动： - 在执行INSERT时将DateCreated和DateUpdated字段设置为现在 - 在执行更新时将DateUpdated字段设置为现在

当我自动说，我的意思是我希望能够这样做：

poco.Name = "Changing the name";
repository.Save();

不是这个：

poco.Name = "Changing the name";
poco.LastModified = DateTime.Now;
repository.Save();

在幕后，“某事”应该自动更新DateTime字段。什么是“东西”？我正在使用Entity Framework 6.0。 EF可以自动执行此操作吗？我知道MySQL可以做这样的事情。或者在SQL Server中使用触发器/存储过程。但我不希望这样。

此问题是此问题的替代和更改版本： Entity Framework/SQL2008 - How to Automatically Update LastModified fields for Entities?

这个问题为EF 4.0提供了一些很好的解决方案/答案。但是我想用EF6.0加DBContext。如果我有更多的时间，我会尝试调整这些解决方案，让他们在EF6.0中工作。但是现在我想知道是否有人已经解决了这个问题，或者知道如何将EF4.0的自定义SaveChanges()或Add()覆盖转录为EF6.0。

Answer 1

您可以覆盖DbContext上的SaveChanges（）方法，以更新Save（）上的DateUpdated值。我会实现一个接口，允许更新一些项目，而不是其他项目。

public interface IEntityAutoDateFields
{
    DateTime DateCreated { get; set; }
    DateTime DateUpdated { get; set; }
}

然后：

public class PocoWithDates : IEntityAutoDateFields
{
    public PocoWithDates()
    {

    }

    public DateTime DateCreated { get; set; }
    public DateTime DateUpdated { get; set; }
}

在你的背景下：

public PocoWithDatesContext : DbContext
{
     public DbSet<PocoWithDates> PocoWithDatesSet { get; set;}

     public override int SaveChanges()
     {
         var now = DateTime.Now;             

         this.ChangeTracker.DetectChanges();
         foreach (var item in this.ChangeTracker.Entries()
                               .Where(i => i.State == EntityState.Added || i.State == EntityState.Modified)
                               .Where(i => i as IEntityAutoDateFields != null))
         {
             if (item.State == EntityState.Added)
             {
                  (item as IEntityAutoDateFields).DateCreated = now;
             }
             (item as IEntityAutoDateFields).DateUpdated = now;
         }
         // Call the SaveChanges method on the context;
         return base.SaveChanges();
     }
}

Answer 2

这是基于Ben Cull solution。我刚刚添加了处理异步方法SaveChangesAsync（）。

1创建基类

public class BaseEntity
{
    public DateTime? DateCreated { get; set; }
    public string UserCreated { get; set; }
    public DateTime? DateModified { get; set; }
    public string UserModified { get; set; }
}

2将Base应用于现有类

public class Student : BaseEntity
{
    public int Id { get; set; }
    public string Name { get; set; }
}

3覆盖DBContext类

中的SaveOn（）和SaveOnSync（）

public class SchoolContext : DbContext
{

public override int SaveChanges()
{
    var entities = ChangeTracker.Entries().Where(x => x.Entity is BaseEntity && (x.State == EntityState.Added || x.State == EntityState.Modified));

    var currentUsername = HttpContext.Current != null && HttpContext.Current.User != null
        ? HttpContext.Current.User.Identity.Name
        : "Anonymous";

    foreach (var entity in entities)
    {
        if (entity.State == EntityState.Added)
        {
            ((BaseEntity)entity.Entity).DateCreated = DateTime.Now;
            ((BaseEntity)entity.Entity).UserCreated = currentUsername;
        }

        ((BaseEntity)entity.Entity).DateModified = DateTime.Now;
        ((BaseEntity)entity.Entity).UserModified = currentUsername;
    }

    return base.SaveChanges();
}
}

public override Task<int> SaveChangesAsync(System.Threading.CancellationToken cancellationToken)

    {
        var entities = ChangeTracker.Entries().Where(x => x.Entity is BaseEntity && (x.State == EntityState.Added || x.State == EntityState.Modified));

        var currentUsername = HttpContext.Current != null && HttpContext.Current.User != null
            ? HttpContext.Current.User.Identity.Name : "Anonymous";


        foreach (var entity in entities)
        {
            if (entity.State == EntityState.Added)
            {
                ((BaseEntity)entity.Entity).DateCreated = DateTime.Now;
                ((BaseEntity)entity.Entity).UserCreated = currentUsername;
            }

            ((BaseEntity)entity.Entity).DateModified = DateTime.Now;
            ((BaseEntity)entity.Entity).UserModified = currentUsername;
        }

        return base.SaveChangesAsync(cancellationToken);
    }
    }

Answer 3

添加一个构造函数，在实体的新实例上设置DateCreated / DateUpdated。

public class PocoWithDates {
    public PocoWithDates()
    {
        this.DateCreated = DateTime.Now;
        this.DateUpdated = this.DateCreated;
    }

    public string PocoName { get; set; }
    public DateTime DateCreated { get; set; }
    public DateTime DateUpdated { get; set; }
}

就自动修改Save（）上的DateUpdated而言，您可能希望查看here。

如何自动设置DateCreated和DateUpdated

3 个答案: