首先使用代码保存和还原断开连接的实体的正确方法是什么？ [英] What is the right way to save and restore a disconnected entity using code first?

问题描述

为了存储用户的屏幕首选项，我拥有要在程序启动时检索并在程序结束时保存的ScreenSettings实体。

So that I can store the user's screen preferences, I have ScreenSettings entity that I want to retrieve when the program starts and save when the program ends.

为此我不想保持上下文开放的原因。

For this reason I don't want to keep the context open.

我想知道这样做的最佳方法。
我尝试了以下
，但是我对SaveSettings函数不满意，因为它会删除并重新添加对象。

I am wondering about the best way to do this. I have tried the following however I am not comfortable with the SaveSettings function because it deletes and re-adds the object.

我该如何

namespace ClassLibrary1
{
using System.ComponentModel.DataAnnotations;
using System.Data.Entity;

//Domain Class
public class ScreenSetting
{
    #region Properties

    public int Id { get; set; }

    [Required]
    public int WindowLeft { get; set; }

    [Required]
    public int WindowTop { get; set; }

    #endregion
}

// Context
public class Context : DbContext
{
    #region Properties

    public DbSet<ScreenSetting> ScreenSettings { get; set; }

    #endregion
}

// UI
public class UI
{
    #region Public Methods

    // Get the settings object
    public ScreenSetting GetSettings(int SettingsId)
    {
        var Db = new Context();
        ScreenSetting settings = Db.ScreenSettings.Find(SettingsId);
        if (settings == null)
        {
            settings = new ScreenSetting { Id = SettingsId, WindowTop = 100, WindowLeft = 100 };
            Db.ScreenSettings.Add(settings);
        }
        Db.Dispose();
        return settings;
    }

    // Save the settings object
    public void SaveSettings(ScreenSetting settings)
    {
        var Db = new Context();
        ScreenSetting oldSettings = Db.ScreenSettings.Find(settings.Id);
        if (oldSettings == null)
        {
            Db.ScreenSettings.Add(settings);
        }
        else
        {
            Db.ScreenSettings.Remove(oldSettings);
            Db.ScreenSettings.Add(settings);
        }
        Db.Dispose();
    }

    public void test()
    {
        ScreenSetting setting = this.GetSettings(1);
        setting.WindowLeft = 500;
        setting.WindowTop = 500;
        this.SaveSettings(setting);
    }

    #endregion

    #region Methods

    private static void Main()

    {
        var o = new UI();
        o.test();
    }

    #endregion
}
}

推荐答案

您遇到了常见的模式，更新或插入，这种模式是如此普遍以至于它有一个名称： upsert 。当一种模式很常见时，通常也有一个通用的解决方案。

You ran into a common pattern, update or insert, which is so common that it's got a name: upsert. When a pattern is common, usually there also is a common solution.

在 System.Data.Entity.Migrations 没有扩展方法 AddOrUpdate 完全满足您的要求：

In System.Data.Entity.Migrations there is an extension method AddOrUpdate that does exactly what you want:

public void SaveSettings(ScreenSetting settings)
{
    using (var db = new Context())
    {
        db.ScreenSettings.AddOrUpdate(settings);
        db.SaveChanges();
    }
}

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