Question

我有一个包含许多子实体的庞大表单，因此，我使用Automapper将树对象填充为EF对象。然后我想更新DB中的类似实体。任何方式将其附加到上下文？

我试着这样做：

        // ApplicationDriver has many child objects
        Infrastructure.Asset.ApplicationDriver driver = mapper.Map<Infrastructure.Asset.ApplicationDriver>(model);

        // get similar object from DB
        Infrastructure.Asset.ApplicationDriver currentApplication = db.ApplicationDrivers.Where(p => p.ApplicationId == model.ApplicationId).FirstOrDefault();

        if (currentApplication == null)
        {
            db.ApplicationDrivers.Add(driver);
        }
        else
        {
            // try to attach driver to current context. 
            // I want to 'replace' current object with all child objects in DB
            db.ApplicationDrivers.Attach(driver);
            currentApplication = driver;
        }
        await db.SaveChangesAsync();

我收到错误：

“附加”Infrastructure.Asset.ApplicationDriver“类型的实体失败，因为同一类型的另一个实体已经相同主键值。使用“附加”方法或时，可能会发生这种情况将实体的状态设置为“未更改”或“已修改”（如果有）图中的实体具有冲突的键值。这可能是因为某些实体是新的，尚未收到数据库生成的密钥值。在这种情况下，使用“添加”方法或“已添加”实体状态跟踪图形，然后将非新实体的状态设置为 “视情况而定”或“修改”。“

我试试：

        var currentApplication = db.ApplicationDrivers.Where(p => p.ApplicationId == model.ApplicationId).FirstOrDefault();

        if (currentApplication == null)
        {
            db.ApplicationDrivers.Add(driver);
        }
        else
        {
            driver.Id = currentApplication.Id;
            db.ApplicationDrivers.Attach(driver);
        }
        await db.SaveChangesAsync();

并得到同样的错误。什么是不正确的以及如何解决此问题，而无需手动将所有子对象的每个属性从驱动程序复制到currentApplication？

Answer 1

如果要更新数据库，则无需附加到实体，并将db替换为当前对象：

    // ApplicationDriver has many child objects
    Infrastructure.Asset.ApplicationDriver driver = mapper.Map<Infrastructure.Asset.ApplicationDriver>(model);

    // get similar object from DB
    Infrastructure.Asset.ApplicationDriver currentApplication = db.ApplicationDrivers.Where(p => p.ApplicationId == model.ApplicationId).FirstOrDefault();

    if (currentApplication == null)
    {
        db.ApplicationDrivers.Add(driver);
    }
    else
    {
        //this will attach, and set state to modified
        //same as previous question, make sure you virtual properties are not populated to avoid unwanted duplicates. 
        db.Entry(driver).State = System.Data.Entity.EntityState.Modified; 
        currentApplication = driver;
    }
    await db.SaveChangesAsync();

Answer 2

我找到了一篇文章：

https://www.devtrends.co.uk/blog/stop-using-automapper-in-your-data-access-code

似乎，最好不要使用automapper将DTO映射到EF以进行编辑。

将带有树的实体附加到EF

2 个答案: