EF Core - 添加具有唯一索引的数据时出现重复键错误

Question

我正在尝试使用 EF Core 向数据库添加数据，但我无法克服重复键错误：Cannot insert duplicate key row in object 'dbo.Stocks' with unique index 'IX_Stocks_Name'. The duplicate key value is (stock1).

我有实体Stock 与Transaction 具有一对多关系 - 一个Stock 可以与许多Transactions 相关联。

仅当数据库中没有具有给定 ID 的 Stock 时才会出现问题 - 在这种情况下，我可以添加许多具有相同 StockID 的 Transactions 并且它可以工作：

using(var context = dbContextFactory.CreateDbContext(new string[0]))
     {
        List<Transaction> list = new List<Transaction>();
        //If there's no Stock with ID "stock1" in the database the code works.
        //Executing the code for the second time results in error, however, if I changed stock1 to stock2 it would work 
        var stock1 = new Stock("stock1");
        list.AddRange(new Transaction[]
        {
        //I can add two exactly the same `Transaction`s and it's ok when executed on a fresh database
        new Transaction(stock1, DateTime.Now, 1M, 5),
        new Transaction(stock1, DateTime.Now, 1M, 5),
        });
        context.Transactions.AddRange(list);
        context.SaveChanges();
     }

下面我添加了类的定义及其IEntityTypeConfigurations。

提前感谢任何提示。

Transaction类：

public class Transaction
    {
        public Stock RelatedStock { get; set; }
        public DateTime TransactionTime { get; set; }
        public Decimal Price { get; set; }
        public int Volume { get; set; }
        public Transaction() { }
    }

TransactionConfiguration类：

public class TransactionConfiguration : IEntityTypeConfiguration<Transaction>
    {
        public void Configure(EntityTypeBuilder<Transaction> builder)
        {
            builder
                .ToTable("Transactions");

            builder
                .Property<int>("TransactionID")
                .HasColumnType("int")
                .ValueGeneratedOnAdd()
                .HasAnnotation("Key", 0);

            builder
                .Property(transaction => transaction.Price)
                .HasColumnName("Price")
                .IsRequired();

            builder
                .Property(transaction => transaction.TransactionTime)
                .HasColumnName("Time")
                .IsRequired();

            builder
                .Property(transaction => transaction.Volume)
                .HasColumnName("Volume")
                .IsRequired();

            builder
                .HasIndex("RelatedStockStockID", nameof(Transaction.TransactionTime))
                .IsUnique();
        }
    }

Stock类：

public class Stock
  {
     public string Name { get; set; }
     public ICollection<Transaction> Transactions { get; set; }
     public Stock() { }
  }

StockConfiguration类：

public class StockConfiguration : IEntityTypeConfiguration<Stock>
    {
        public void Configure(EntityTypeBuilder<Stock> builder)
        {
            builder
                .ToTable("Stocks");

            builder
                .Property<int>("StockID")
                .HasColumnType("int")
                .ValueGeneratedOnAdd()
                .HasAnnotation("Key", 0);

            builder
                .Property(stock => stock.Name)
                .HasColumnName("Name")
                .HasMaxLength(25)
                .IsRequired();

            builder
                .HasMany(stock => stock.Transactions)
                .WithOne(transaction => transaction.RelatedStock)
                .IsRequired();

            builder
                .HasIndex(stock => stock.Name)
                .IsUnique();
        }
    }

Answer 1

dbo.Stocks 表上有一个名为 IX_Stocks_Name 的唯一索引。你违反了这个索引。

你的问题是这一行：

var stock1 = new Stock("stock1");

您一遍又一遍地创建“stock1”。相反，您应该首先检索（或存储）“stock1”的Stock 实体并使用它，如果它已经存在的话。如果它不存在，那么创建一个是安全的。

简而言之，代码是用现有的Name 将INSERT 转换为dbo.Stocks。

Answer 2

您需要检查是否存在已知的所需 ID 的 Stock。为了你的例子：

var stock1 = context.Stocks.SingleOrDefault(x => x.StockId == "stock1") ?? new Stock("stock1");

如果数据库中已有库存，这将关联现有库存，如果没有，则关联新库存。

Answer 3

感谢@Zer0 和@Steve Py 的建议，我想出了以下解决方案：

void Insert(IEnumerable<Transaction> data)
        {
            using(var context = dbContextFactory.CreateDbContext(new string[0]))
            {
                List<Stock> stocks = data.Select(s => s.RelatedStock).Distinct(new StockComparer()).ToList();
                context.AddRange(stocks);
                context.SaveChanges();
                stocks = context.Stocks.ToList();

                List<Transaction> newList = new List<Transaction>(data.Count());

                foreach (var t in data)
                {
                        Stock relatedStock = stocks.Where(s => s.Name == t.RelatedStock.Name).First();
                        t.RelatedStock = relatedStock;
                        newList.Add(t);
                }

                context.Transactions.AddRange(newList);
                context.SaveChanges();
            }
        }