【发布时间】：2017-07-26 09:49:57
【问题描述】：
我正在开发一个 C# 控制台应用程序，该应用程序从激战 2 API 下载数据并使用 Entity Framework 6 将其输入到我的数据库中。我正在尝试使用多线程，以便我可以加快输入过程大量数据进入我的数据库。
问题是当代码在我的AddRecipes 方法中运行到我的DBContext.SaveChanges() 调用时，返回以下错误：
违反主键约束“PK_dbo.Items”。无法在对象“dbo.Items”中插入重复键。重复键值为 (0)。
这是与我的问题相关的代码部分：
class Program
{
private static ManualResetEvent resetEvent;
private static int nIncompleteThreads = 0;
//Call this function to add to the dbo.Items table
private static void AddItems(object response)
{
string strResponse = (string)response;
using (GWDBContext ctx = new GWDBContext())
{
IEnumerable<Items> itemResponse = JsonConvert.DeserializeObject<IEnumerable<Items>>(strResponse);
ctx.Items.AddRange(itemResponse);
ctx.SaveChanges();
}
if (Interlocked.Decrement(ref nIncompleteThreads) == 0)
{
resetEvent.Set();
}
}
//Call this function to add to the dbo.Recipes table
private static void AddRecipes(object response)
{
string strResponse = (string)response;
using (GWDBContext ctx = new GWDBContext())
{
IEnumerable<Recipes> recipeResponse = JsonConvert.DeserializeObject<IEnumerable<Recipes>>(strResponse);
ctx.Recipes.AddRange(recipeResponse);
foreach(Recipes recipe in recipeResponse)
{
ctx.Ingredients.AddRange(recipe.ingredients);
}
ctx.SaveChanges(); //This is where the error is thrown
}
if (Interlocked.Decrement(ref nIncompleteThreads) == 0)
{
resetEvent.Set();
}
}
static void GetResponse(string strLink, string type)
{
//This method calls the GW2 API through HTTPWebRequest
//and store the responses in a List<string> responseList variable.
GWHelper.GetAllResponses(strLink);
resetEvent = new ManualResetEvent(false);
nIncompleteThreads = GWHelper.responseList.Count();
//ThreadPool.QueueUserWorkItem creates threads for multi-threading
switch (type)
{
case "I":
{
foreach (string strResponse in GWHelper.responseList)
{
ThreadPool.QueueUserWorkItem(new WaitCallback(AddItems), strResponse);
}
break;
}
case "R":
{
foreach (string strResponse in GWHelper.responseList)
{
ThreadPool.QueueUserWorkItem(new WaitCallback(AddRecipes), strResponse);
}
break;
}
}
//Waiting then resetting event and clearing the responseList
resetEvent.WaitOne();
GWHelper.responseList.Clear();
resetEvent.Dispose();
}
static void Main(string[] args)
{
string strItemsLink = "items";
string strRecipesLink = "recipes";
GetResponse(strItemsLink, "I");
GetResponse(strRecipesLink, "R");
Console.WriteLine("Press any key to continue...");
Console.ReadLine();
}
这是我的 DBContext 类：
public class GWDBContext : DbContext
{
public GWDBContext() : base("name=XenoGWDBConnectionString") { }
public DbSet<Items> Items { get; set; }
public DbSet<Recipes> Recipes { get; set; }
public DbSet<Ingredient> Ingredients { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
}
}
这也是我的表类（我知道名称令人困惑，我正在重写它们）：
public class Items
{
public Items()
{
Recipes = new HashSet<Recipes>();
Ingredients = new HashSet<Ingredient>();
}
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.None)] //This attribute makes sure that the id column is not an identity column since the api is sending that).
public int id { get; set; }
.../...
public virtual ICollection<Recipes> Recipes { get; set; }
public virtual ICollection<Ingredient> Ingredients { get; set; }
}
public class Recipes
{
public Recipes()
{
disciplines = new List<string>();
ingredients = new HashSet<Ingredient>();
}
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.None)] //This attribute makes sure that the id column is not an identity column since the api is sending that).
public int id { get; set; }
public string type { get; set; }
[ForeignKey("Items")] //This attribute points the output_item_id column to the Items table.
.../...
private List<string> _disciplines { get; set; }
public List<string> disciplines
{
get { return _disciplines; }
set { _disciplines = value; }
}
[Required]
public string DisciplineAsString
{
//get; set;
get { return string.Join(",", _disciplines); }
set { _disciplines = value.Split(',').ToList(); }
}
public string chat_link { get; set; }
public virtual ICollection<Ingredient> ingredients { get; set; }
public virtual Items Items { get; set; }
}
public class Ingredient
{
public Ingredient()
{
Recipe = new HashSet<Recipes>();
}
[Key]
public int ingredientID { get; set; }
[ForeignKey("Items")] //This attribute points the item_id column to the Items table.
public int item_id { get; set; }
public int count { get; set; }
public virtual ICollection<Recipes> Recipe { get; set; }
public virtual Items Items { get; set; }
}
以下链接解释了 Items/Recipes 类返回的内容：
我注意到在删除外键约束和public virtual Items Items { get; set; } 代码后，数据将被正确保存。我相信我的错误与在 Recipes 类中使用 public virtual Items Items 有关。但据我了解，我需要在类中包含该虚拟变量，以便实体框架可以知道类之间的关系。那么为什么在我的类中有这个虚拟变量会导致主键冲突被抛出呢？
【问题讨论】：
-
这表示您的 ID 重复为 0。这表明您实际上并未设置 ID。你确定你确实得到了一个 id 字段并且它被正确地反序列化到你的对象中吗？
-
我在错误行检查时有 0 个项目。食谱正在正确反序列化，并且在 AddRecipes 调用之前已正确插入项目。
-
食谱上的项目是否也正确？只是想知道你是否有一些 ID 为 0 的项目或其他东西......
-
类和链接的 json 对象之间存在相当大的不匹配。
-
我认为这只是由于在插入成分时重新插入了现有的
Items对象，但我必须查看recipeResponse的确切内容才能验证这一点。
标签： c# multithreading entity-framework ef-code-first primary-key