阻止更新 EF-core 中的导航属性

Question

请问，当我们创建新的主实体时，如何防止 EF.core 尝试插入/更新外键表？

抛出此异常：

SqlException: Cannot insert explicit value for identity column in table 'clients' when IDENTITY_INSERT is set to OFF.
Cannot insert explicit value for identity column in table 'guards' when IDENTITY_INSERT is set to OFF.
Cannot insert explicit value for identity column in table 'penalties' when IDENTITY_INSERT is set to OFF.

我的代码如下：

  public class Offence
  {
    [Key]
    public Int32 offence_id { get; set; }

    public Int32? guard_id { get; set; }
    public Int32? penalty_id { get; set; }
    public DateTime? dt_recorded { get; set; }
    public Int32? salary_id { get; set; }
    public Decimal? amount { get; set; }
    public String status { get; set; }
    public Int32? site_id { get; set; }

    public Guard Guard { get; set; }
    public Salary Salary { get; set; }
    public Site Site { get; set; }
    public Penalty Penalty { get; set; }
  }

任何创建新 Offence 的尝试都会出错，因为 EF.core 会尝试为相关导航属性运行插入：

public Guard Guard { get; set; }
public Salary Salary { get; set; }
public Site Site { get; set; }
public Penalty Penalty { get; set; }

我们如何防止这种情况发生？

编辑：创建和更新代码

[HttpPost]
public async Task<IActionResult> Create([FromBody] Offence o)
{
  if (o == null)
  {
    return BadRequest();
  }

  o.last_modified_by = int.Parse(((ClaimsIdentity)User.Identity).Claims.FirstOrDefault(c => c.Type == ClaimTypes.NameIdentifier)?.Value);
  o.last_modified = DateTime.Now;

  await db.AddAsync(o);
  await db.SaveChangesAsync();

  return CreatedAtRoute("GetOffenceAsync", new { id = o.offence_id }, o);
}

Answer 1

要让它工作，我必须在保存之前null-out 导航属性。

但是，如果使用CreatedAtRoute 发送回初始对象，则需要缓存nulled-out 属性并在返回之前将它们添加回：

实际代码：

[HttpPost]
public async Task<IActionResult> Create([FromBody] Offence o)
{
  if (o == null)
  {
    return BadRequest();
  }

  o.last_modified_by = int.Parse(((ClaimsIdentity)User.Identity).Claims.FirstOrDefault(c => c.Type == ClaimTypes.NameIdentifier)?.Value);
  o.last_modified = DateTime.Now;

  var _g = o.Guard;
  var _p = o.Penalty;
  var _s = o.Site;

  o.Guard = null;
  o.Penalty = null;
  o.Site = null;

  await db.AddAsync(o);
  await db.SaveChangesAsync();

  o.Guard = _g;
  o.Penalty = _p;
  o.Site = _s;

  return CreatedAtRoute("GetOffenceAsync", new { id = o.offence_id }, o);
}

Answer 2

您的导航属性似乎有值，请在保存之前检查您的导航属性是否有空引用； EF Core 保存逻辑尝试保存导航属性（如果它们具有值）。

如果有用请告诉我

Answer 3

您需要将这些属性设置为virtual。这样 EF 就知道模型的组成部分以及导航属性是什么。这也将启用您需要的 LazyLoading 机制。

public virtual Guard Guard { get; set; }
public virtual Salary Salary { get; set; }
public virtual Site Site { get; set; }
public virtual Penalty Penalty { get; set; }