LINQ to SQL 正确地延迟加载映射类

Question

这是我第一次这样做，当我想向数据库添加新项目时，它失败了。

如何设置文章类中的ArticleCategoryId属性来引用文章中的文章类别，因为此时它为空并且不包含任何值？我的课程如下：

文章类：

[Table(Name="Articles")]
public class Article
{        
    [HiddenInput(DisplayValue=false)]
    [Column(IsPrimaryKey=true, IsDbGenerated=true,AutoSync=AutoSync.OnInsert)]
    public int ArticleId { get; set; }

    [Column(Name="ArticleCategoryId", AutoSync = AutoSync.Never)]
    [Mapping.Association(IsForeignKey = true, Name = "FK_Articles_ArticleCategorys")]
    public ArticleCategories ArticleCategory{get;set;}

    [Column]
    public string Label { get; set; }

    [DataType(DataType.MultilineText)]
    [Column]
    public string Text { get; set; }

    [DataType(DataType.DateTime)]
    [Column]
    public DateTime Created { get; set; }
}

类别类：

[Table(Name = "ArticleCategorys")]
public class ArticleCategories
{
    [HiddenInput(DisplayValue = false)]
    [Column(IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert, Name="ArticleCategoryId")]
    public int ArticleCategoryId { get; set; }

    [Column]
    public string Name { get; set; }        

    [Column]
    public string Description { get; set; }

    [DataType(DataType.DateTime)]
    [Column] public DateTime Created { get; set; }
}

我的错误：

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Create([Bind(Exclude = "ArticleId")] Article article)
{
    try
    {
        ArticleCategories category = articleCategoriesRepository.ArticleCategories.FirstOrDefault(x => x.ArticleCategoryId == article.ArticleCategory.ArticleCategoryId);
        article.ArticleCategory = category;
        article.Created = DateTime.Now;
        articlesRepository.SaveArticle(article);
        ViewData["Message"] = NudaJeFuc.WebUI.Properties.Resources.text_ArticleSaved;
        return RedirectToAction("Index");        
    }
    catch
    {
        return view();
    }
}

Answer 1

我遇到了 Linq2SQL 映射的问题，当您向数据库添加新列时，它不会更新，因此会失败。

因此，我必须删除 .edmx 文件，并在对数据库进行更改时重新添加它。

ADO.NET 实体框架不会发生这种情况，所以如果可以的话请尝试一下。

Answer 2

找到解决方案，感谢史蒂文·桑德森

[Table(Name="Articles")]
public class Article
{        
    [HiddenInput(DisplayValue=false)]
    [Column(IsPrimaryKey=true, IsDbGenerated=true,AutoSync=AutoSync.OnInsert)]
    public int ArticleId { get; set; }

    [Column]
    internal int ArticleCategoryId { get; set; }

    internal EntityRef<ArticleCategories> _ArticleCategoryId;

    //[Column(AutoSync = AutoSync.OnInsert, Name = "ArticleCategoryId")]
    [Association(ThisKey="ArticleCategoryId", Storage="_ArticleCategoryId")]
    public ArticleCategories ArticleCategory
    {
        get
        {
            return _ArticleCategoryId.Entity;
        }
        set
        {
            ArticleCategoryId = value.ArticleCategoryId;
            _ArticleCategoryId.Entity = value;                
        }
    }

    [Column]
    public string Label { get; set; }

    [DataType(DataType.MultilineText)]
    [Column]
    public string Text { get; set; }

    [Required(ErrorMessage = "Musíte vybrat kategorii článku.")]
    [DataType(DataType.DateTime)]
    [Column]
    public DateTime Created { get; set; }
}