在实体框架核心中更新具有一对多关系的连接实体答案

【问题标题】：Updating connected entities with one-to-many relationships in entity framework core在实体框架核心中更新具有一对多关系的连接实体
【发布时间】：2019-03-01 06:44:46
【问题描述】：

我有一个一对多的关系，我正在尝试更新但收到错误

数据库操作预计会影响 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。有关理解和处理乐观并发异常的信息，请参阅 http://go.microsoft.com/fwlink/?LinkId=527962。

更新

只要受益人集合没有被更改或更新，更新方法将一直有效。

代码看起来像

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，但我可能错了。

我还尝试使用更改跟踪器通过如下方法进行更新

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？

【问题讨论】：

标签： c# entity-framework-core

【解决方案1】：

在阅读了更新的工作原理后，我终于取得了进展。基本上就像提到的here ，还有这个issue。当调用 Update 方法时，整个实体的状态（包括通过导航属性可到达的所有实体）被标记为已修改。如果您尝试将受益人添加到现有员工，SaveChanges() 将抛出，因为它希望使用提供的主键修改记录，但在数据库中找不到。更新方法似乎不是最佳选择。

我选择在 EmployeeRepository 中将存储库库中的 Update 方法设置为可覆盖，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);
        }
    }
}

我相信这个答案可以改进或调整以适应特定情况。例如，除了清除持久化集合之外，还可以选择更新

【讨论】：