Entity framework 不保存对象属性

Question

我正在开发在线商店，使用 ASP.Net MVC 4 框架。

我有一个对象类别 — 商店中商品的类别（例如男装）：

public class Category
{
    [Required]
    public long id { get; set; }

    [Required]
    public string name { get; set; }

    public bool active { get; set; }
    public bool displayOnTop { get; set; }
    public bool showSubcategoriesItems { get; set; }

    public Category parentCategory { get; set; }

    public virtual Collection<Item> items { get; set; }

    public Category()
    {
        this.items = new Collection<Item>();
    }
}

有一个属性 parentCategory — 这意味着该类别包含在另一个类别中（例如男装 > 衬衫）。

要编辑现有类别，我使用以下操作：

[HttpPost]
public ActionResult EditCategory(Category editedCategory, string parentCategorySelector)
{
    UsersContext db = new UsersContext();

    Category existingCategory = db.categories.SingleOrDefault(c => c.id == editedCategory.id);
    long parentCategoryId = (long)Int32.Parse(parentCategorySelector);
    Category parentCategory = db.categories.SingleOrDefault(c => c.id == parentCategoryId);

    if (existingCategory == null) return RedirectToAction("Index", "Admin");

    existingCategory.name = editedCategory.name;
    existingCategory.active = editedCategory.active;
    existingCategory.displayOnTop = editedCategory.displayOnTop;
    existingCategory.showSubcategoriesItems = editedCategory.showSubcategoriesItems;
    existingCategory.parentCategory = parentCategory;

    db.Entry(existingCategory.parentCategory).State = EntityState.Modified;
    db.SaveChanges();

    return View(existingCategory);
}

一切正常，除了当我想将 parentCategory 设置为 null 时 — 它在代码中设置为 null，但 null 值没有保存到数据库中 — 以前的值仍然存在。

但是如果我这样做的话：

[HttpPost]
public ActionResult EditCategory(Category editedCategory, string parentCategorySelector)
{
    UsersContext db = new UsersContext();

    Category existingCategory = db.categories.SingleOrDefault(c => c.id == editedCategory.id);
    long parentCategoryId = (long)Int32.Parse(parentCategorySelector);
    Category parentCategory = db.categories.SingleOrDefault(c => c.id == parentCategoryId);

    if (existingCategory == null) return RedirectToAction("Index", "Admin");

    existingCategory.name = editedCategory.name;
    existingCategory.active = editedCategory.active;
    existingCategory.displayOnTop = editedCategory.displayOnTop;
    existingCategory.showSubcategoriesItems = editedCategory.showSubcategoriesItems;
    existingCategory.parentCategory = null;

    db.Entry(existingCategory.parentCategory).State = EntityState.Modified;
    db.SaveChanges();

    return View(existingCategory);
}

即我无条件设置为null，保存正确

我做错了什么？

Answer 1

为什么Category.id下没有Key属性？如果 id 是主键，它必须存在。

你应该使用 Include 到 load relate entities:

   [HttpPost]
    public ActionResult EditCategory(Category editedCategory, string parentCategorySelector)
    {
        using(UsersContext db = new UsersContext())
        {
            Category existingCategory = db.categories.Include(c => c.parentCategory).SingleOrDefault(c => c.id == editedCategory.id);
            long parentCategoryId = (long)Int32.Parse(parentCategorySelector);
            Category parentCategory = db.categories.SingleOrDefault(c => c.id == parentCategoryId);

            if (existingCategory == null) return RedirectToAction("Index", "Admin");

            existingCategory.name = editedCategory.name;
            existingCategory.active = editedCategory.active;
            existingCategory.displayOnTop = editedCategory.displayOnTop;
            existingCategory.showSubcategoriesItems = editedCategory.showSubcategoriesItems;
            existingCategory.parentCategory = parentCategory;

            db.SaveChanges();

            return View(existingCategory);
        }
    }

请注意，DbContext 是如何正确处理的。

Entity framework 不保存对象属性

Entity framework doesn't save object property

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Entity framework 不保存对象 属性

Entity framework doesn't save object property

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Entity framework 不保存对象属性