entity-framework-4 - Entity Framework 不会将外键值更新为null

Question

我无法在我的Entity Framework 4.3代码优先数据库中获取要更新为null的外键。

我的 View 模型:

public class AccountViewModel
{
    public int Id { get; set; }
    public int? CorporationId { get; set; } 
    public CorporationModel Corporation { get; set; }
}

var corporation = db.Corporation.Where(x => x.Id == model.CorporationId).FirstOrDefault();  // shows as null
account.Corporation = corporation;  // sets the value to null

db.Entry(account).State = EntityState.Modified;
db.SaveChanges();  // does not save the null value in the FK field!!!

任何帮助将不胜感激。

Answer 1

您必须将外键属性设置为null。将状态设置为Modified仅会影响标量属性(外键属性是其中之一，但导航属性则不受影响):

account.CorporationId = null;

db.Entry(account).State = EntityState.Modified;
db.SaveChanges();

如果您在 Account上没有外键属性，则必须加载包括公司在内的帐户:

var account = db.Account.Include(a => a.Corporation)
    .Where(a => a.Id == accountId)
    .SingleOrDefault();

if (account != null)
{
    account.Corporation = null;
    db.SaveChanges();
}