Question

我经常搜索但失败了......我试图创建两个表，一个表有另一个表的外键（具体来说， Url_Entries ＆＃39; url成为 WordCount 类的外键。但是当我使用代码优先向数据库添加一个对象时，我得到了异常。

System.InvalidOperationException未被用户代码处理的HResult = -2146233079 消息=属性＆＃39; url＆＃39;无法配置为导航属性。该属性必须是有效的实体类型，并且该属性应具有非抽象的getter和setter。对于集合属性，类型必须实现ICollection，其中T是有效的实体类型。来源=的EntityFramework 堆栈跟踪：在System.Data.Entity.ModelConfiguration.Configuration.ConventionTypeConfiguration.NavigationProperty（PropertyPath propertyPath）在System.Data.Entity.ModelConfiguration.Configuration.ConventionTypeConfiguration.NavigationProperty（PropertyInfo propertyInfo）在System.Data.Entity.ModelConfiguration.Conventions.ForeignKeyPrimitivePropertyAttributeConvention.Apply（PropertyInfo memberInfo，ConventionTypeConfiguration配置，ForeignKeyAttribute属性）在System.Data.Entity.ModelConfiguration.Conventions.PropertyAttributeConfigurationConvention 1.<.ctor>b__0(ConventionTypeConfiguration ec) at System.Data.Entity.ModelConfiguration.Conventions.TypeConvention.ApplyCore(Type memberInfo, ModelConfiguration modelConfiguration) at System.Data.Entity.ModelConfiguration.Conventions.TypeConventionBase.Apply(Type memberInfo, ModelConfiguration modelConfiguration) at System.Data.Entity.ModelConfiguration.Configuration.ConventionsConfiguration.ApplyModelConfiguration(Type type, ModelConfiguration modelConfiguration) at System.Data.Entity.ModelConfiguration.Conventions.Convention.ApplyModelConfiguration(Type type, ModelConfiguration modelConfiguration) at System.Data.Entity.ModelConfiguration.Configuration.ConventionsConfiguration.ApplyModelConfiguration(Type type, ModelConfiguration modelConfiguration) at System.Data.Entity.ModelConfiguration.Mappers.TypeMapper.MapEntityType(Type type) at System.Data.Entity.DbModelBuilder.MapTypes(EdmModel model) at System.Data.Entity.DbModelBuilder.Build(DbProviderManifest providerManifest, DbProviderInfo providerInfo) at System.Data.Entity.DbModelBuilder.Build(DbConnection providerConnection) at System.Data.Entity.Internal.LazyInternalContext.CreateModel(LazyInternalContext internalContext) at System.Data.Entity.Internal.RetryLazy 2.GetValue（TInput输入）在System.Data.Entity.Internal.LazyInternalContext.InitializeContext（）在System.Data.Entity.Internal.InternalContext.Initialize（）在System.Data.Entity.Internal.InternalContext.GetEntitySetAndBaseTypeForType（Type entityType）在System.Data.Entity.Internal.Linq.InternalSet 1.Initialize() at System.Data.Entity.Internal.Linq.InternalSet 1.get_InternalContext（） at System.Data.Entity.Internal.Linq.InternalSet 1.ActOnSet(Action action, EntityState newState, Object entity, String methodName) at System.Data.Entity.Internal.Linq.InternalSet 1.Add（Object entity）在System.Data.Entity.DbSet`1.Add（TEntity实体）在WebCrawler.save（Hashtable hashTable，String url）中的c：\ Users \ Muhammad Rehan \ Documents \ Visual Studio 2013 \ WebSites \ WebSite7 \ App_Code \ WebCrawler.cs：第110行在C：\ Users \ Muhammad Rehan \ Documents \ Visual Studio 2013 \ WebSites \ WebSite7 \ App_Code \ WebCrawler.cs中的WebCrawler.countAndSave（String content，String url）：第104行 at index.Unnamed_Click（Object sender，EventArgs e）位于c：\ Users \ Muhammad Rehan \ Documents \ Visual Studio 2013 \ WebSites \ WebSite7 \ index.aspx.cs：第19行在System.Web.UI.WebControls.Button.OnClick（EventArgs e）在System.Web.UI.WebControls.Button.RaisePostBackEvent（String eventArgument）在System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent（String eventArgument）在System.Web.UI.Page.RaisePostBackEvent（IPostBackEventHandler sourceControl，String eventArgument）在System.Web.UI.Page.RaisePostBackEvent（NameValueCollection postData）在System.Web.UI.Page.ProcessRequestMain（Boolean includeStagesBeforeAsyncPoint，Boolean includeStagesAfterAsyncPoint） InnerException：

public class Url_Entries
{
    public Url_Entries(string url)
    {
        this.Url = url;
    }
    [Key]
    public string Url { get; set; }

    [Required, DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public DateTime date { get; set; }

    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int crawl_id { get; set; }
}



public class WordCount
{
    public WordCount(string url, string word, int count)
    {
      this.url = url;
      this.word = word;
      this.count = count;
    }
  public Url_Entries Url_Entries { get; set; }
  public string url { get; set; }
  [Required, ForeignKey("url")]
  public string word { get; set; }
  public int count { get; set; }

}




public class MyDbContext:DbContext
{
    public MyDbContext()
        : base("ExploreCalifornia")
    {

    }

    public DbSet<Url_Entries> Url_Entries { get; set; }
    public DbSet<WordCount> WordCount { get; set; }
}





public class WebCrawler
{
    public static MyDbContext db = new MyDbContext();
    private static void save(Hashtable hashTable, string url)
    {
        Url_Entries newUrlEntry = new Url_Entries(url);
        db.Url_Entries.Add(newUrlEntry); //Exception on this line
    }
}

上一课中的例外情况。我发表了评论。

Answer 1

您在错误字段上设置ForeignKey - 属性。您希望url成为Url_Entries的外键，目前您将word设置为url的外键。

这部分错了：

public Url_Entries Url_Entries { get; set; }
public string url { get; set; }
[Required, ForeignKey("url")]
public string word { get; set; }

更改为：

  [ForeignKey("url")]
  public Url_Entries Url_Entries { get; set; }
  [Required]
  public string url { get; set; }
  public string word { get; set; }

要更详细地解释您正在获得的错误：您正在尝试将类型为string的字段设置为string类型字段的外键。该错误告诉您，表示另一个实体的属性（称为导航属性）必须是“有效实体类型”。有效的实体类型是一个复杂的类型，它代表另一个表，因此string是不可接受的。

System.InvalidOperationException - CodeFirst

1 个答案: