Question

我正在向大约6家银行插入5000笔交易，但我在数据库中获得了5000个银行行，并且名称重复。

public class Transaction
{
    [Key]
    public int Id { get; set; }
    public DateTime TransDate { get; set; }
    public decimal Value { get; set; }
    public string Description { get; set; }
    public Bank Bank { get; set; }
}

public class Bank
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
}

public class FinancialRecordContext : DbContext
{
    public FinancialRecordContext() : base("FinancialRecordDatabase") { }

    public DbSet<Transaction> Transactions { get; set; }

    public DbSet<Bank> Banks { get; set; }

    public Bank FindOrInsertBank(string bankName)
    {
        var bank = Banks.SingleOrDefault(b => b.Name == bankName);
        if (bank == null)
        {
            bank = new Bank { Name = bankName };
            Banks.Add(bank);
        }
        return bank;
    }
}

然后插入我循环浏览一些数据并插入：

        using (var context = new FinancialRecordContext())
        {
            foreach (var t in data)
            {
                var tran = new Transaction
                {
                    Description = t.Description,
                    Value = t.Value,
                    TransDate = t.TransDate,
                    Bank = context.FindOrInsertBank(t.BankName)
                };
                context.Transactions.Add(tran);
            }
            context.SaveChanges();
        }

似乎FindOrInsertBank方法一直进入数据库，而不是在本地查看最近添加的，但未提交的银行。我该怎么做/应该这样做？

每次银行插入后我应SaveChanges吗？不是我想要做的事情，我希望这是一次交易。

Answer 1

您可以尝试查询更改跟踪器（这是内存中查询，而不是数据库查询）：

using (var context = new FinancialRecordContext())
{
    foreach (var t in data)
    {
        Bank bank = context.ChangeTracker.Entries()
            .Where(e => e.Entity is Bank && e.State != EntityState.Deleted)
            .Select(e => e.Entity as Bank)
            .SingleOrDefault(b => b.Name == t.BankName);

        if (bank == null)
            bank = context.FindOrInsertBank(t.BankName);

        var tran = new Transaction
        {
            Description = t.Description,
            Value = t.Value,
            TransDate = t.TransDate,
            Bank = bank
        };
        context.Transactions.Add(tran);
    }
    context.SaveChanges();
}

修改

在这里使用更改跟踪器可能对性能不利，因为Bank.Name不是实体的关键，我想查询将是对条目的线性搜索。在这种情况下，使用手写字典可能是更好的解决方案：

using (var context = new FinancialRecordContext()) { var dict = new Dictionary<string, Bank>(); foreach (var t in data) { Bank bank; if (!dict.TryGetValue(t.BankName, out bank)) { bank = context.FindOrInsertBank(t.BankName); dict.Add(t.BankName, bank); } var tran = new Transaction { Description = t.Description, Value = t.Value, TransDate = t.TransDate, Bank = bank }; context.Transactions.Add(tran); } context.SaveChanges(); }

Answer 2

尝试一些建议：

1）先检查Local DbSet<Bank>的{{1}}集合。

public Bank FindOrInsertBank(string bankName)
{
    var bank = Banks.Local.SingleOrDefault(b => b.Name == bankName);
    if (bank == null)
    {
        var bank = Banks.SingleOrDefault(b => b.Name == bankName);
        if (bank == null)
        {
            bank = new Bank { Name = bankName };
            Banks.Add(bank);
        }
    }
    return bank;
}

2）每次更新后强制拨打DetectChanges()

context.Transactions.Add(tran);
context.ChangeTracker.DetectChanges();

我该如何防止多次插入？

2 个答案: