说一些关于ObjectId的事
MongoDB确实是最像关系型数据库的NoSQL，这在它主键设计上可以体现的出来，它并没有采用自动增长主键，因为在分布式服务器之间做数据同步很麻烦，而是采用了一种ObjectId的方式，它生成方便，占用空间比long多了4个字节，（12个字节）在数据表现层面也说的过去，它是一种以时间，机器，进程和自增几个因素组合的方式来体现的，可以近似看成是按时间的先后进行排序的，对于ObjectId的生成我们可以通过MongoDB服务端去获得，或者在客户端也有对它的集成，使用方便，一般情况下，在客户端实体类中只要定义一个ObjectId类型的属性，这个属性就默认被赋上值了，应该说，还是比较方便的，由于它存储是一种字符串，所以，一般客户端，像NoRM都为我们实现了对string类型的隐藏转换，应该说，还是比较友好的！
ObjectId的组成
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" alt="" />
为何选择十六进制表示法
在C#版的NoRM这样设计ObjectId
/// <summary>
/// Generates a byte array ObjectId.
/// </summary>
/// <returns>
/// </returns>
public static byte[] Generate()
{
var oid = new byte[];
var copyidx = ;
//时间差
Array.Copy(BitConverter.GetBytes(GenerateTime()), , oid, copyidx, );
copyidx += ;
//机器码
Array.Copy(machineHash, , oid, copyidx, );
copyidx += ;
//进程码
Array.Copy(procID, , oid, copyidx, );
copyidx += ;
//自增值
Array.Copy(BitConverter.GetBytes(GenerateInc()), , oid, copyidx, );
return oid;
}
完整的ObjectId类型源代码
它重写的ToString()方法，为的是实现byte[]到string串之间的类型转换，并且为string和ObjectId对象实现 implicit的隐式类型转换，方便开发人员在实际中最好的使用它们，需要注意的是在byte[]中存储的数据都是以十六进制的形式体现的
/// <summary>
/// Represents a Mongo document's ObjectId
/// </summary>
[System.ComponentModel.TypeConverter(typeof(ObjectIdTypeConverter))]
public class ObjectId
{
private string _string; /// <summary>
/// Initializes a new instance of the <see cref="ObjectId"/> class.
/// </summary>
public ObjectId()
{
} /// <summary>
/// Initializes a new instance of the <see cref="ObjectId"/> class.
/// </summary>
/// <param retval="value">
/// The value.
/// </param>
public ObjectId(string value)
: this(DecodeHex(value))
{
} /// <summary>
/// Initializes a new instance of the <see cref="ObjectId"/> class.
/// </summary>
/// <param retval="value">
/// The value.
/// </param>
internal ObjectId(byte[] value)
{
this.Value = value;
} /// <summary>
/// Provides an empty ObjectId (all zeros).
/// </summary>
public static ObjectId Empty
{
get { return new ObjectId(""); }
} /// <summary>
/// Gets the value.
/// </summary>
/// <value>The value.</value>
public byte[] Value { get; private set; } /// <summary>
/// Generates a new unique oid for use with MongoDB Objects.
/// </summary>
/// <returns>
/// </returns>
public static ObjectId NewObjectId()
{
// TODO: generate random-ish bits.
return new ObjectId { Value = ObjectIdGenerator.Generate() };
} /// <summary>
/// Tries the parse.
/// </summary>
/// <param retval="value">
/// The value.
/// </param>
/// <param retval="id">
/// The id.
/// </param>
/// <returns>
/// The try parse.
/// </returns>
public static bool TryParse(string value, out ObjectId id)
{
id = Empty;
if (value == null || value.Length != )
{
return false;
} try
{
id = new ObjectId(value);
return true;
}
catch (FormatException)
{
return false;
}
} /// <summary>
/// Implements the operator ==.
/// </summary>
/// <param retval="a">A.</param>
/// <param retval="b">The b.</param>
/// <returns>The result of the operator.</returns>
public static bool operator ==(ObjectId a, ObjectId b)
{
if (ReferenceEquals(a, b))
{
return true;
} if (((object)a == null) || ((object)b == null))
{
return false;
} return a.Equals(b);
} /// <summary>
/// Implements the operator !=.
/// </summary>
/// <param retval="a">A.</param>
/// <param retval="b">The b.</param>
/// <returns>The result of the operator.</returns>
public static bool operator !=(ObjectId a, ObjectId b)
{
return !(a == b);
} /// <summary>
/// Returns a hash code for this instance.
/// </summary>
/// <returns>
/// A hash code for this instance, suitable for use in hashing algorithms and data structures like a hash table.
/// </returns>
public override int GetHashCode()
{
return this.Value != null ? this.ToString().GetHashCode() : ;
} /// <summary>
/// Returns a <see cref="System.String"/> that represents this instance.
/// </summary>
/// <returns>
/// A <see cref="System.String"/> that represents this instance.
/// </returns>
public override string ToString()
{
if (this._string == null && this.Value != null)
{
this._string = BitConverter.ToString(this.Value).Replace("-", string.Empty).ToLower();
} return this._string;
} /// <summary>
/// Determines whether the specified <see cref="System.Object"/> is equal to this instance.
/// </summary>
/// <param retval="o">
/// The <see cref="System.Object"/> to compare with this instance.
/// </param>
/// <returns>
/// <c>true</c> if the specified <see cref="System.Object"/> is equal to this instance; otherwise, <c>false</c>.
/// </returns>
public override bool Equals(object o)
{
var other = o as ObjectId;
return this.Equals(other);
} /// <summary>
/// Equalses the specified other.
/// </summary>
/// <param retval="other">
/// The other.
/// </param>
/// <returns>
/// The equals.
/// </returns>
public bool Equals(ObjectId other)
{
return other != null && this.ToString() == other.ToString();
} /// <summary>
/// Decodes a HexString to bytes.
/// </summary>
/// <param retval="val">
/// The hex encoding string that should be converted to bytes.
/// </param>
/// <returns>
/// </returns>
protected static byte[] DecodeHex(string val)
{
var chars = val.ToCharArray();
var numberChars = chars.Length;
var bytes = new byte[numberChars / ]; for (var i = ; i < numberChars; i += )
{
bytes[i / ] = Convert.ToByte(new string(chars, i, ), );
} return bytes;
} /// <summary>TODO::Description.</summary>
public static implicit operator string(ObjectId oid)
{
return oid == null ? null : oid.ToString();
} /// <summary>TODO::Description.</summary>
public static implicit operator ObjectId(String oidString)
{
ObjectId retval = ObjectId.Empty;
if(!String.IsNullOrEmpty(oidString))
{
retval = new ObjectId(oidString);
}
return retval;
}
}
ObjectIdGenerator源代码
它主要实现了ObjectId串生成的规则及方式
/// <summary>
/// Shameless-ly ripped off, then slightly altered from samus' implementation on GitHub
/// http://github.com/samus/mongodb-csharp/blob/f3bbb3cd6757898a19313b1af50eff627ae93c16/MongoDBDriver/ObjectIdGenerator.cs
/// </summary>
internal static class ObjectIdGenerator
{
/// <summary>
/// The epoch.
/// </summary>
private static readonly DateTime epoch = new DateTime(, , , , , , DateTimeKind.Utc); /// <summary>
/// The inclock.
/// </summary>
private static readonly object inclock = new object(); /// <summary>
/// The inc.
/// </summary>
private static int inc; /// <summary>
/// The machine hash.
/// </summary>
private static byte[] machineHash; /// <summary>
/// The proc id.
/// </summary>
private static byte[] procID; /// <summary>
/// Initializes static members of the <see cref="ObjectIdGenerator"/> class.
/// </summary>
static ObjectIdGenerator()
{
GenerateConstants();
} /// <summary>
/// Generates a byte array ObjectId.
/// </summary>
/// <returns>
/// </returns>
public static byte[] Generate()
{
var oid = new byte[];
var copyidx = ;
//时间差
Array.Copy(BitConverter.GetBytes(GenerateTime()), , oid, copyidx, );
copyidx += ;
//机器码
Array.Copy(machineHash, , oid, copyidx, );
copyidx += ;
//进程码
Array.Copy(procID, , oid, copyidx, );
copyidx += ;
//自增值
Array.Copy(BitConverter.GetBytes(GenerateInc()), , oid, copyidx, );
return oid;
} /// <summary>
/// Generates time.
/// </summary>
/// <returns>
/// The time.
/// </returns>
private static int GenerateTime()
{
var now = DateTime.Now.ToUniversalTime(); var nowtime = new DateTime(epoch.Year, epoch.Month, epoch.Day, now.Hour, now.Minute, now.Second, now.Millisecond);
var diff = nowtime - epoch;
return Convert.ToInt32(Math.Floor(diff.TotalMilliseconds));
} /// <summary>
/// Generate an increment.
/// </summary>
/// <returns>
/// The increment.
/// </returns>
private static int GenerateInc()
{
lock (inclock)
{
return inc++;
}
} /// <summary>
/// Generates constants.
/// </summary>
private static void GenerateConstants()
{
machineHash = GenerateHostHash();
procID = BitConverter.GetBytes(GenerateProcId());
} /// <summary>
/// Generates a host hash.
/// </summary>
/// <returns>
/// </returns>
private static byte[] GenerateHostHash()
{
using (var md5 = MD5.Create())
{
var host = Dns.GetHostName();
return md5.ComputeHash(Encoding.Default.GetBytes(host));
}
} /// <summary>
/// Generates a proc id.
/// </summary>
/// <returns>
/// Proc id.
/// </returns>
private static int GenerateProcId()
{
var proc = Process.GetCurrentProcess();
return proc.Id;
}
}
事实上，通过对NoRm这个MongoDB客户端的学习，让我们的眼界放宽了许多，可能在思考问题时不局限于眼前，对于同一个问题可以会有更多的解决方法了，呵呵！