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。
问题是当代码运行到我的 AddRecipes 方法中的 DBContext.SaveChanges() 调用时，返回以下错误:
Violation of PRIMARY KEY constraint 'PK_dbo.Items'. Cannot insert duplicate key in object 'dbo.Items'. The duplicate key value is (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(我知道名称很困惑，我正在努力重写它们):
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;放; } 代码数据将被正确保存。我相信我的错误与 Recipes 类中的 public virtual Items Items 有关。但是根据我的理解，我需要在类中有那个虚拟变量，这样 Entity Framework 才能知道类之间的关系。那么，为什么在我的类中使用该虚拟变量会导致抛出主键违规？
最佳答案
您只需要食谱中的项目列表。如果您需要搜索哪些食谱有特定项目，您可以通过搜索 Recipe 的外键(Item 的主键)来实现。
代码存在一个基本的命名缺陷。您有一个 Recipes 类，然后是一个名为 Recipes 的食谱列表。与项目相同。
然后您有一个用于 Recipes 的外键 [ForeignKey("Items")]。这是哪些项目？列表或对象项。它很容易出错。
将您的类重命名为Recipe 和Item
public class Recipe
{
public Recipe()
public class Item
{
public Item()
此外 - 如评论中所述，0 的重复 Id 听起来好像没有设置 Id。
查看食谱链接:
{
.../...
"ingredients": [
{ "item_id": 19684, "count": 50 },
{ "item_id": 19721, "count": 1 },
{ "item_id": 46747, "count": 10 }
],
"id": 7319,
.../...
}
食谱不应包含项目列表，而应包含配料列表。类结构应该是:
Recipe has:
public virtual ICollection<Ingredient> Ingredients { get; set; }
Ingredient has:
public virtual ICollection<Item> Items { get; set; }
Item 类没有 Ingredients 或 Recipes 列表，这些列表是通过使用与 Item 的主键匹配的外键查询 Ingredient 上的数据库 Items 来检索的，或者食谱外键上的数据库成分与成分的主键匹配 - 然后您可以进行连接以查找这些成分的任何项目。
所以做如下修改:
无需在 Item 类中提及 Recipe 或 Ingredients。
public Item() // remove pluralisation
{
// Remove these from the constructor,
// Recipes = new HashSet<Recipes>();
// Ingredients = new HashSet<Ingredient>();
}
// remove these from the class.
// public virtual ICollection<Recipes> Recipes { get; set; }
// public virtual ICollection<Ingredient> Ingredients { get; set; }
一种成分有很多元素 - 因此是元素的集合
public Ingredient()
{
// You don't need a collection of Recipes -
// you need a collection of Items.
// Recipe = new HashSet<Recipes>();
}
.../...
[ForeignKey("Item")] // change this
public Item Item // include an Item object - the PK of the
// Item is the FK of the Ingredient
.../...
// Remove Recipes
// public virtual ICollection<Recipes> Recipe { get; set; }
public virtual ICollection<Item> Items { get; set; }
我更喜欢 using the object name for the variable Item Item .
一个食谱有很多配料 - 因此是配料的集合
public Recipes()
{
disciplines = new List<string>();
ingredients = new HashSet<Ingredient>();
}
.../...
// [ForeignKey("Items")] remove this
[ForeignKey("Ingredient")]
public Ingredient Ingredient // include as Ingredient object
// the PK of the Ingredient is the FK for the Recipe
.../...
public virtual ICollection<Ingredient> Ingredients { get; set; }
// The Recipe does not have an Item, the Ingredient has
// has a collection of <Item> Items
// public virtual Items Items { get; set; }
此外，我不确定您为什么要使用哈希集。如果您没有特别的理由使用它们，我会将它们制作成列表。
如果这不能修复您的代码，我将检查它的其余部分。
关于c# - 多线程 EF6 中的主键冲突，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45260221/