顺序GUID

Question

我正在创建asp.net mvc4示例。在此我在datacontext的Sample表中创建了Id列作为GUID。

public class Sample
{
    [Required]
    public Guid ID { get; set; }
    [Required]
    public string FirstName { get; set; }
}

这是实体表

CreateTable(
"dbo.Samples",
 c => new
 {
     ID = c.Guid(nullable: false),
     FirstName = c.String(nullable: false)                   
 })
 .PrimaryKey(t => t.ID);

Id传递00000000-0000-0000-0000-000000000000。

如何将newid()设置为GUID以及我必须设置的位置。

Answer 1

我建议您只使用long作为您的ID类型。它只是工作＆＃34;与GUID相比有一些性能提升。但是如果你想使用GUID，你应该使用Sequential GUID并在构造函数中设置它。我还会将ID设为private setter：

public class Sample
{
    public Sample() {
        ID = GuidComb.Generate();
    }
    [Required]
    public Guid ID { get; private set; }
    [Required]
    public string FirstName { get; set; }
}

顺序GUID

public static class GuidComb
    {
        public static Guid Generate()
        {
            var buffer = Guid.NewGuid().ToByteArray();

            var time = new DateTime(0x76c, 1, 1);
            var now = DateTime.Now;
            var span = new TimeSpan(now.Ticks - time.Ticks);
            var timeOfDay = now.TimeOfDay;

            var bytes = BitConverter.GetBytes(span.Days);
            var array = BitConverter.GetBytes(
                (long)(timeOfDay.TotalMilliseconds / 3.333333));

            Array.Reverse(bytes);
            Array.Reverse(array);
            Array.Copy(bytes, bytes.Length - 2, buffer, buffer.Length - 6, 2);
            Array.Copy(array, array.Length - 4, buffer, buffer.Length - 4, 4);

            return new Guid(buffer);
        }
    }

Answer 2

这也可以通过属性来完成：

[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid AddressID { get; set; }

Answer 3

我在Nlog日志记录到数据库时遇到了同样的问题。我所做的是故意打开迁移文件并进行以下更改

CreateTable(
"dbo.Samples",
c => new
{
     ID = c.Guid(nullable: false,identity:true),
     FirstName = c.String(nullable: false)
})
.PrimaryKey(t => t.ID);

identity参数实际上创建了defaultvalue为newsequentialid()的表格在表中。

Answer 4

如果我们忽略周围的政治因素（如果这是个好主意），那么@TombMedia的答案很可能就是您想要的。

但是，如果您需要向现有表中添加新列，并希望指定newId（）用作默认值，因为该字段不可为空，则可以在迁移类中使用它：

AddColumn(
    "dbo.Samples",
    "UUID", 
    c => c.Guid(nullable: false, defaultValueSql: "newId()")
);

注意：这是一个古老的问题，在EF6中仍然很重要，在寻求有关如何在EF迁移中使用newId的帮助时，排名很高，这就是为什么要添加此答案。

Answer 5

保罗的答案是正确的，但顺序指导的实施可以得到改善。如果在同一台服务器上创建，This implementation of sequential guid会更频繁地增加并阻止相同的数字。

要阻止link rot，请输入以下代码：

public class SequentialGuid
{

    public DateTime SequenceStartDate { get; private set; }
    public DateTime SequenceEndDate { get; private set; }

    private const int NumberOfBytes = 6;
    private const int PermutationsOfAByte = 256;
    private readonly long _maximumPermutations = (long)Math.Pow(PermutationsOfAByte, NumberOfBytes);
    private long _lastSequence;

    public SequentialGuid(DateTime sequenceStartDate, DateTime sequenceEndDate)
    {
        SequenceStartDate = sequenceStartDate;
        SequenceEndDate = sequenceEndDate;
    }

    public SequentialGuid()
        : this(new DateTime(2011, 10, 15), new DateTime(2100, 1, 1))
    {
    }

    private static readonly Lazy<SequentialGuid> InstanceField = new Lazy<SequentialGuid>(() => new SequentialGuid());
    internal static SequentialGuid Instance
    {
        get
        {
            return InstanceField.Value;
        }
    }

    public static Guid NewGuid()
    {
        return Instance.GetGuid();
    }

    public TimeSpan TimePerSequence
    {
        get
        {
            var ticksPerSequence = TotalPeriod.Ticks / _maximumPermutations;
            var result = new TimeSpan(ticksPerSequence);
            return result;
        }
    }

    public TimeSpan TotalPeriod
    {
        get
        {
            var result = SequenceEndDate - SequenceStartDate;
            return result;
        }
    }

    private long GetCurrentSequence(DateTime value)
    {
        var ticksUntilNow = value.Ticks - SequenceStartDate.Ticks;
        var result = ((decimal)ticksUntilNow / TotalPeriod.Ticks * _maximumPermutations - 1);
        return (long)result;
    }

    public Guid GetGuid()
    {
        return GetGuid(DateTime.Now);
    }

    private readonly object _synchronizationObject = new object();
    internal Guid GetGuid(DateTime now)
    {
        if (now < SequenceStartDate || now > SequenceEndDate)
        {
            return Guid.NewGuid(); // Outside the range, use regular Guid
        }

        var sequence = GetCurrentSequence(now);
        return GetGuid(sequence);
    }

    internal Guid GetGuid(long sequence)
    {
        lock (_synchronizationObject)
        {
            if (sequence <= _lastSequence)
            {
                // Prevent double sequence on same server
                sequence = _lastSequence + 1;
            }
            _lastSequence = sequence;
        }

        var sequenceBytes = GetSequenceBytes(sequence);
        var guidBytes = GetGuidBytes();
        var totalBytes = guidBytes.Concat(sequenceBytes).ToArray();
        var result = new Guid(totalBytes);
        return result;
    }

    private IEnumerable<byte> GetSequenceBytes(long sequence)
    {
        var sequenceBytes = BitConverter.GetBytes(sequence);
        var sequenceBytesLongEnough = sequenceBytes.Concat(new byte[NumberOfBytes]);
        var result = sequenceBytesLongEnough.Take(NumberOfBytes).Reverse();
        return result;
    }

    private IEnumerable<byte> GetGuidBytes()
    {
        var result = Guid.NewGuid().ToByteArray().Take(10).ToArray();
        return result;
    }
}

Answer 6

我知道这个问题很老，但如果有人有这样的问题，我建议这样的解决方案：

protected Guid GetNewId()
{
    SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["YourConnectionString"].ConnectionString);
    var query = "select newid()";
    conn.Open();
    SqlCommand com = new SqlCommand(query, conn);
    var guid = new Guid(com.ExecuteScalar().ToString());
    conn.Close();
    return guid;
}

您可以在创建新对象时从SQL数据库获取newid。对我来说它有效。 :)（但我不知道这是好习惯）

如何使用它：

var myNewGuidValue = GetNewId();

Answer 7

在使用Entity Framework Core 2.1.1时，我使用：

[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid UserId { get; set; }

然后在迁移中，添加defaultValueSql参数，如下所示：

migrationBuilder.CreateTable(
    name: "Users",
    columns: table => new
    {
         UserId = table.Column<Guid>(nullable: false, defaultValueSql: "newsequentialid()"),
         DisplayName = table.Column<string>(nullable: true)
    },
       constraints: table =>
    {
        table.PrimaryKey("PK_Users", x => x.UserId);
    });

这可以确保sql服务器负责生成顺序的guid，这将比滚动自己的guid更好。

如果您不希望使用顺序向导的缺点，则可以使用“ newid（）”代替。

如何在实体框架中为GUID设置NewId（）

7 个答案:

顺序GUID