Question

我有一对多关系，正在尝试更新但收到错误消息

数据库操作预期会影响1行，但实际上会影响0行。自加载实体以来，数据可能已被修改或删除。有关了解和处理乐观并发异常的信息，请参见http://go.microsoft.com/fwlink/?LinkId=527962。

已更新

只要受益人集合没有更改或更新，更新方法就可以使用。

代码类似于

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }

    private readonly List<Beneficiary> _beneficiaries;
    public IEnumerable<Beneficiary> Beneficiaries => _beneficiaries;

    public void AddBeneficiary(string name)
    {
        var beneficiary = new Beneficiary(Id, name);
        _beneficiaries.Add(beneficiary);
    }
}

public sealed class Beneficiary
{
    public int Id { get; set; }
    public int EmployeeId { get; private set; }
    public string Name { get; private set; }

    public Beneficiary(int employeeId, string name)
    {
        Name = name;
        EmployeeId = employeeId;
    }
}

//Extracted from repo method
public void Update(TEntity entity)
{
    if (entity != null)
        _dbSet.Update(entity);
}

// Extracted Actual update from application service
if (incomingEmployee.Beneficiaries.Any())
{
    if (employeeFromStore.Beneficiaries.Any())
    {
        employeeFromStore.Beneficiaries.ToList()
            .ForEach(existingBeneficiary => 
        employeeFromStore.RemoveBeneficiary(existingBeneficiary)); //Method skipped for brevity

        //Tried calling this too
        //_employeeRepository.UnitOfWork.SaveChanges();
    }

    incomingEmployee.Beneficiaries.ToList().ForEach(beneficiary =>
    {
        employeeFromStore.AddBeneficiary(beneficiary.Name);
    });
}

_employeeRepository.Update(employeeFromStore);
_employeeRepository.UnitOfWork.SaveChanges();

我觉得问题在于跟踪器如何处理导航属性集合的更新，但我可能是错的。

我还试图通过以下方法使用变更跟踪器进行更新

public void ApplyCurrentValues<TEntity>(TEntity original, TEntity current)
        where TEntity : class
{
    //if it is not attached, attach original and set current values
    base.Entry<TEntity>(original).CurrentValues.SetValues(current);
}

有人知道怎么做吗？

Answer 1

在阅读了有关更新的工作原理后，我终于取得了进展。基本上如上所述here ，以及此issue。调用Update方法时，整个实体的状态（包括所有通过导航属性可访问的实体）的状态都标记为已修改。如果您试图将受益人添加到现有员工中，则SaveChanges（）会抛出异常，因为它希望使用提供的主键来修改记录，但在数据库中找不到该记录。更新方法似乎不是最佳选择。

我选择使EmployeeRepository中的存储库库中的Update方法可重写，如下所示

//Update method in the repository base
//Made method virtual to enable overriding
public virtual void Update(TEntity entity)
{
    if (entity != null)
        _dbSet.Update(entity);
}

//Update method from EmployeeRepository
public override void Update(Employee employee)
{
    var employeeFromStore = _unitOfWork.Employees.Where(p => p.Id == employee.Id)
        .Include(p => p.Beneficiaries)
        .SingleOrDefault();

    if (employeeFromStore != null)
    {
        context.Entry(employeeFromStore).CurrentValues.SetValues(employee);

        //Replacing the whole collection
        foreach (var beneficiary in employeeFromStore.Beneficiaries)
        {
            if (employee.Beneficiaries.Any())
                context.Entry(beneficiary).State = EntityState.Deleted;
        }

        //Adding new collection
        foreach (var beneficiaryToAdd in employee.Beneficiaries)
        {
            var newBeneficiary = new Beneficiary(beneficiaryToAdd.EmployeeId, beneficiaryToAdd.Name);

            employeeFromStore.AddBeneficiary(newBeneficiary.Name);
        }
    }
}

我相信，可以针对特定情况对这一答案进行改进或调整。例如，除了清除保留的收藏集之外，还可以选择更新

在实体框架核心中使用一对多关系更新连接的实体

1 个答案: