Question

我正在从前端改变实体，将其映射到后端，只是想在数据库中更新它。更新的执行情况如下：

[HttpPut("{id}")]
    public IActionResult Update(string id, [FromBody]Worker worker)
    {
        using (var dbContext= new MyDbContext())
        {
            dbContext.ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;

            var entity = dbContext.Workers.FirstOrDefault(r => r.Id == worker.Id);

            if (entity == null) return BadRequest();

            dbContext.Workers.Update(worker);
            dbContext.SaveChanges();
            return Ok();
        }}

在执行此操作之前，我正在获取用户列表并将其发送到前端。尽管我将QueryTrackingBehavior设置为NoTracking，但是却出现异常：

System.InvalidOperationException: 'The instance of entity type 'Contract' cannot be tracked because another instance with the key value 'Id:4' is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.'

合同是与工人相关的实体，已更新...

知道我在做什么错吗？

更新：

工人-合同关系：

   public class Worker: IId
{
    public int Id { get; set; }
    public ICollection<Contract> Contracts{ get; set; }
}
 public class Contract: IId
{
    public int Id { get; set; }
    public int WorkerId { get; set; }
    public Worker Worker { get; set; }
}

Answer 1

好吧！在您的代码中遇到了问题。您没有将更新后的实体映射到从数据库中拉出的现有实体。您必须将更新的实体映射到现有实体。为此，您可以使用AutoMapper或显式映射，如下所示：

您可以解决以下问题：

[HttpPut("{id}")]
public IActionResult Update(string id, [FromBody]Worker worker)
{
        using (var dbContext= new MyDbContext())
        {
            var entityToBeUpdated = dbContext.Workers.AsNoTracking().FirstOrDefault(r => r.Id == worker.Id);

            if (entity == null) return BadRequest();

            entityToBeUpdated.Property1 = worker.Property1;
            entityToBeUpdated.Property2 = worker.Property2;
            // Do the same for the other changed properties as well

            dbContext.Workers.Update(entityToBeUpdated);
            dbContext.SaveChanges();
            return Ok();
        }
 }

或者，您也可以尝试以下操作：

[HttpPut("{id}")]
public IActionResult Update(string id, [FromBody]Worker worker)
{
      using (var dbContext= new MyDbContext())
      {
           var entityToBeUpdated = dbContext.Workers.FirstOrDefault(r => r.Id == worker.Id);

           if (entity == null) return BadRequest();

           entityToBeUpdated.Property1 = worker.Property1;
           entityToBeUpdated.Property2 = worker.Property2;
           // Do the same for the other changed properties as well.

           dbContext.SaveChanges();
           return Ok();
      }
}

EF Core 2.0更新-跟踪问题

1 个答案: