EF5自动生成主键GUID

Question

我使用Guids作为主键在我的数据库中的实体，使用asp.net 4.5 web表单的模型绑定功能，当我插入一个记录在数据库中使用实体框架5我做的事情像

public void onInsert([Control("ControlID")] int? countryID){
 if(countryID.hasValue){
    var DbEntityToInsert = new DbEntity(); //where DbEntity is the class generated by the EF
    TryUpdateModel(DbEntityToInsert);
    DbEntityToInsert.GuidPK = Guid.NewGuid();
    if(Page.ModelState.IsValid){
     using(var db = new DatabaseContext()){
      db.Add(DbEntityToInsert);
      db.Save();
     }//using ends
    }//modelstate.isvalid if ends
  }//countryid.hasvalue ends
 }//main method ends

现在我想问是否有一种方法可以告诉EF在插入新记录时为PK生成一个Guid，这样我就不必写

行了

  DbEntityToInsert.GuidPK = Guid.NewGuid();

Answer 1

您可以尝试在派生上下文中重写SaveChanges。主要任务是找出一个实体是否有GuidPK属性作为主键。下面是使用反射的尝试:

public override int SaveChanges()
{
    this.ChangeTracker.DetectChanges();
    var addedEntities = this.ChangeTracker.Entries()
        .Where(e => e.State == EntityState.Added)
        .Select(e => new
        {
            Entity = e.Entity,
            PropertyInfo = e.Entity.GetType().GetProperty("GuidPK")
        })
        .Where(x => x.PropertyInfo != null && x.PropertyInfo.CanWrite);
    foreach (var x in addedEntities)
        x.PropertyInfo.SetValue(x.Entity, Guid.NewGuid());
    return base.SaveChanges();
}

为了避免这里的反射，你可以有一个共同的接口，由所有使用GuidPK属性作为PK的实体实现:

public interface IEntityWithGuidPK
{
    Guid GuidPK { get; set; }
}
public class DbEntity : IEntityWithGuidPK
{
    public Guid GuidPK { get; set; }
    // ...
}

则SaveChanges中的代码为:

    //...
    var addedEntities = this.ChangeTracker.Entries()
        .Where(e => e.State == EntityState.Added &&
            e.Entity is IEntityWithGuidPK)
        .Select(e => e.Entity as IEntityWithGuidPK);
    foreach (var e in addedEntities)
        e.GuidPK = Guid.NewGuid();
    //...