本文主要是介绍.NET生成MongoDB中的主键ObjectId，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
前言
因为很多场景下我们需要在创建MongoDB数据的时候提前生成好主键为了返回或者通过主键查询创建的业务，像EF中我们可以生成Guid来，本来想着要不要实现一套MongoDB中ObjectId的，结果发现网上各种各样的实现都有，不过好在阅读C#MongoDB驱动mongo-csharp-driver代码的时候发现有ObjectId.GenerateNewId()的方法提供，我们可以直接调用即可，不需要我们在花费多余的时间设计重写了。
MongoDB ObjectId类型概述
每次插入一条数据系统都会自动插入一个_id键，键值不可以重复，它可以是任何类型的，也可以手动的插入，默认情况下它的数据类型是ObjectId，由于MongoDB在设计之初就是用作分布式数据库，所以使用ObjectId可以避免不同数据库中_id的重复（如果使用自增的方式在分布式系统中就会出现重复的_id的值）。
ObjectId使用12字节的存储空间，每个字节可以存储两个十六进制数字，所以一共可以存储24个十六进制数字组成的字符串，在这24个字符串中，前8位表示时间戳，接下来6位是一个机器码，接下来4位表示进程id，最后6位表示计数器。
MongoDB 采用 ObjectId 来表示主键的类型，数据库中每个文档都拥有一个_id 字段表示主键，_id 的生成规则如下：
其中包括：4-byte Unix 时间戳，3-byte 机器 ID，2-byte 进程 ID，3-byte 计数器(初始化随机)。
601e2b6b a3203c c89f 2d31aa↑ ↑ ↑ ↑时间戳 机器码 进程ID 随机数MongoDB.Driver驱动安装
1、直接命令自动安装
Install-Package MongoDB.Driver2、搜索Nuget手动安装
调用生成主键ObjectId
var primarykeyId = ObjectId.GenerateNewId();
//输出：641c54b2e674000035001dc2mongo-csharp-driver ObjectId详解
关于ObjectId的生成原理大家阅读如下源码即可。
源码地址：https://github.com/mongodb/mongo-csharp-driver/blob/ec74978f7e827515f29cc96fba0c727828e8df7c/src/MongoDB.Bson/ObjectModel/ObjectId.cs
/* Copyright 2010-present MongoDB Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/using System;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Security;
using System.Threading;namespace MongoDB.Bson
{/// <summary>/// Represents an ObjectId (see also BsonObjectId)./// </summary>
#if NET45[Serializable]
#endifpublic struct ObjectId : IComparable<ObjectId>, IEquatable<ObjectId>, IConvertible{// private static fieldsprivate static readonly ObjectId __emptyInstance = default(ObjectId);private static readonly int __staticMachine = (GetMachineHash() + GetAppDomainId()) & 0x00ffffff;private static readonly short __staticPid = GetPid();private static int __staticIncrement = (new Random()).Next();// private fieldsprivate readonly int _a;private readonly int _b;private readonly int _c;// constructors/// <summary>/// Initializes a new instance of the ObjectId class./// </summary>/// <param name="bytes">The bytes.</param>public ObjectId(byte[] bytes){if (bytes == null){throw new ArgumentNullException("bytes");}if (bytes.Length != 12){throw new ArgumentException("Byte array must be 12 bytes long", "bytes");}FromByteArray(bytes, 0, out _a, out _b, out _c);}/// <summary>/// Initializes a new instance of the ObjectId class./// </summary>/// <param name="bytes">The bytes.</param>/// <param name="index">The index into the byte array where the ObjectId starts.</param>internal ObjectId(byte[] bytes, int index){FromByteArray(bytes, index, out _a, out _b, out _c);}/// <summary>/// Initializes a new instance of the ObjectId class./// </summary>/// <param name="timestamp">The timestamp (expressed as a DateTime).</param>/// <param name="machine">The machine hash.</param>/// <param name="pid">The PID.</param>/// <param name="increment">The increment.</param>public ObjectId(DateTime timestamp, int machine, short pid, int increment): this(GetTimestampFromDateTime(timestamp), machine, pid, increment){}/// <summary>/// Initializes a new instance of the ObjectId class./// </summary>/// <param name="timestamp">The timestamp.</param>/// <param name="machine">The machine hash.</param>/// <param name="pid">The PID.</param>/// <param name="increment">The increment.</param>public ObjectId(int timestamp, int machine, short pid, int increment){if ((machine & 0xff000000) != 0){throw new ArgumentOutOfRangeException("machine", "The machine value must be between 0 and 16777215 (it must fit in 3 bytes).");}if ((increment & 0xff000000) != 0){throw new ArgumentOutOfRangeException("increment", "The increment value must be between 0 and 16777215 (it must fit in 3 bytes).");}_a = timestamp;_b = (machine << 8) | (((int)pid >> 8) & 0xff);_c = ((int)pid << 24) | increment;}/// <summary>/// Initializes a new instance of the ObjectId class./// </summary>/// <param name="value">The value.</param>public ObjectId(string value){if (value == null){throw new ArgumentNullException("value");}var bytes = BsonUtils.ParseHexString(value);FromByteArray(bytes, 0, out _a, out _b, out _c);}// public static properties/// <summary>/// Gets an instance of ObjectId where the value is empty./// </summary>public static ObjectId Empty{get { return __emptyInstance; }}// public properties/// <summary>/// Gets the timestamp./// </summary>public int Timestamp{get { return _a; }}/// <summary>/// Gets the machine./// </summary>public int Machine{get { return (_b >> 8) & 0xffffff; }}/// <summary>/// Gets the PID./// </summary>public short Pid{get { return (short)(((_b << 8) & 0xff00) | ((_c >> 24) & 0x00ff)); }}/// <summary>/// Gets the increment./// </summary>public int Increment{get { return _c & 0xffffff; }}/// <summary>/// Gets the creation time (derived from the timestamp)./// </summary>public DateTime CreationTime{get { return BsonConstants.UnixEpoch.AddSeconds(Timestamp); }}// public operators/// <summary>/// Compares two ObjectIds./// </summary>/// <param name="lhs">The first ObjectId.</param>/// <param name="rhs">The other ObjectId</param>/// <returns>True if the first ObjectId is less than the second ObjectId.</returns>public static bool operator <(ObjectId lhs, ObjectId rhs){return lhs.CompareTo(rhs) < 0;}/// <summary>/// Compares two ObjectIds./// </summary>/// <param name="lhs">The first ObjectId.</param>/// <param name="rhs">The other ObjectId</param>/// <returns>True if the first ObjectId is less than or equal to the second ObjectId.</returns>public static bool operator <=(ObjectId lhs, ObjectId rhs){return lhs.CompareTo(rhs) <= 0;}/// <summary>/// Compares two ObjectIds./// </summary>/// <param name="lhs">The first ObjectId.</param>/// <param name="rhs">The other ObjectId.</param>/// <returns>True if the two ObjectIds are equal.</returns>public static bool operator ==(ObjectId lhs, ObjectId rhs){return lhs.Equals(rhs);}/// <summary>/// Compares two ObjectIds./// </summary>/// <param name="lhs">The first ObjectId.</param>/// <param name="rhs">The other ObjectId.</param>/// <returns>True if the two ObjectIds are not equal.</returns>public static bool operator !=(ObjectId lhs, ObjectId rhs){return !(lhs == rhs);}/// <summary>/// Compares two ObjectIds./// </summary>/// <param name="lhs">The first ObjectId.</param>/// <param name="rhs">The other ObjectId</param>/// <returns>True if the first ObjectId is greather than or equal to the second ObjectId.</returns>public static bool operator >=(ObjectId lhs, ObjectId rhs){return lhs.CompareTo(rhs) >= 0;}/// <summary>/// Compares two ObjectIds./// </summary>/// <param name="lhs">The first ObjectId.</param>/// <param name="rhs">The other ObjectId</param>/// <returns>True if the first ObjectId is greather than the second ObjectId.</returns>public static bool operator >(ObjectId lhs, ObjectId rhs){return lhs.CompareTo(rhs) > 0;}// public static methods/// <summary>/// Generates a new ObjectId with a unique value./// </summary>/// <returns>An ObjectId.</returns>public static ObjectId GenerateNewId(){return GenerateNewId(GetTimestampFromDateTime(DateTime.UtcNow));}/// <summary>/// Generates a new ObjectId with a unique value (with the timestamp component based on a given DateTime)./// </summary>/// <param name="timestamp">The timestamp component (expressed as a DateTime).</param>/// <returns>An ObjectId.</returns>public static ObjectId GenerateNewId(DateTime timestamp){return GenerateNewId(GetTimestampFromDateTime(timestamp));}/// <summary>/// Generates a new ObjectId with a unique value (with the given timestamp)./// </summary>/// <param name="timestamp">The timestamp component.</param>/// <returns>An ObjectId.</returns>public static ObjectId GenerateNewId(int timestamp){int increment = Interlocked.Increment(ref __staticIncrement) & 0x00ffffff; // only use low order 3 bytesreturn new ObjectId(timestamp, __staticMachine, __staticPid, increment);}/// <summary>/// Packs the components of an ObjectId into a byte array./// </summary>/// <param name="timestamp">The timestamp.</param>/// <param name="machine">The machine hash.</param>/// <param name="pid">The PID.</param>/// <param name="increment">The increment.</param>/// <returns>A byte array.</returns>public static byte[] Pack(int timestamp, int machine, short pid, int increment){if ((machine & 0xff000000) != 0){throw new ArgumentOutOfRangeException("machine", "The machine value must be between 0 and 16777215 (it must fit in 3 bytes).");}if ((increment & 0xff000000) != 0){throw new ArgumentOutOfRangeException("increment", "The increment value must be between 0 and 16777215 (it must fit in 3 bytes).");}byte[] bytes = new byte[12];bytes[0] = (byte)(timestamp >> 24);bytes[1] = (byte)(timestamp >> 16);bytes[2] = (byte)(timestamp >> 8);bytes[3] = (byte)(timestamp);bytes[4] = (byte)(machine >> 16);bytes[5] = (byte)(machine >> 8);bytes[6] = (byte)(machine);bytes[7] = (byte)(pid >> 8);bytes[8] = (byte)(pid);bytes[9] = (byte)(increment >> 16);bytes[10] = (byte)(increment >> 8);bytes[11] = (byte)(increment);return bytes;}/// <summary>/// Parses a string and creates a new ObjectId./// </summary>/// <param name="s">The string value.</param>/// <returns>A ObjectId.</returns>public static ObjectId Parse(string s){if (s == null){throw new ArgumentNullException("s");}ObjectId objectId;if (TryParse(s, out objectId)){return objectId;}else{var message = string.Format("'{0}' is not a valid 24 digit hex string.", s);throw new FormatException(message);}}/// <summary>/// Tries to parse a string and create a new ObjectId./// </summary>/// <param name="s">The string value.</param>/// <param name="objectId">The new ObjectId.</param>/// <returns>True if the string was parsed successfully.</returns>public static bool TryParse(string s, out ObjectId objectId){// don't throw ArgumentNullException if s is nullif (s != null && s.Length == 24){byte[] bytes;if (BsonUtils.TryParseHexString(s, out bytes)){objectId = new ObjectId(bytes);return true;}}objectId = default(ObjectId);return false;}/// <summary>/// Unpacks a byte array into the components of an ObjectId./// </summary>/// <param name="bytes">A byte array.</param>/// <param name="timestamp">The timestamp.</param>/// <param name="machine">The machine hash.</param>/// <param name="pid">The PID.</param>/// <param name="increment">The increment.</param>public static void Unpack(byte[] bytes, out int timestamp, out int machine, out short pid, out int increment){if (bytes == null){throw new ArgumentNullException("bytes");}if (bytes.Length != 12){throw new ArgumentOutOfRangeException("bytes", "Byte array must be 12 bytes long.");}timestamp = (bytes[0] << 24) + (bytes[1] << 16) + (bytes[2] << 8) + bytes[3];machine = (bytes[4] << 16) + (bytes[5] << 8) + bytes[6];pid = (short)((bytes[7] << 8) + bytes[8]);increment = (bytes[9] << 16) + (bytes[10] << 8) + bytes[11];}// private static methodsprivate static int GetAppDomainId(){
#if NETSTANDARD1_5 || NETSTANDARD1_6return 1;
#elsereturn AppDomain.CurrentDomain.Id;
#endif}/// <summary>/// Gets the current process id. This method exists because of how CAS operates on the call stack, checking/// for permissions before executing the method. Hence, if we inlined this call, the calling method would not execute/// before throwing an exception requiring the try/catch at an even higher level that we don't necessarily control./// </summary>[MethodImpl(MethodImplOptions.NoInlining)]private static int GetCurrentProcessId(){return Process.GetCurrentProcess().Id;}private static int GetMachineHash(){// use instead of Dns.HostName so it will work offlinevar machineName = GetMachineName();return 0x00ffffff & machineName.GetHashCode(); // use first 3 bytes of hash}private static string GetMachineName(){return Environment.MachineName;}private static short GetPid(){try{return (short)GetCurrentProcessId(); // use low order two bytes only}catch (SecurityException){return 0;}}private static int GetTimestampFromDateTime(DateTime timestamp){var secondsSinceEpoch = (long)Math.Floor((BsonUtils.ToUniversalTime(timestamp) - BsonConstants.UnixEpoch).TotalSeconds);if (secondsSinceEpoch < int.MinValue || secondsSinceEpoch > int.MaxValue){throw new ArgumentOutOfRangeException("timestamp");}return (int)secondsSinceEpoch;}private static void FromByteArray(byte[] bytes, int offset, out int a, out int b, out int c){a = (bytes[offset] << 24) | (bytes[offset + 1] << 16) | (bytes[offset + 2] << 8) | bytes[offset + 3];b = (bytes[offset + 4] << 24) | (bytes[offset + 5] << 16) | (bytes[offset + 6] << 8) | bytes[offset + 7];c = (bytes[offset + 8] << 24) | (bytes[offset + 9] << 16) | (bytes[offset + 10] << 8) | bytes[offset + 11];}// public methods/// <summary>/// Compares this ObjectId to another ObjectId./// </summary>/// <param name="other">The other ObjectId.</param>/// <returns>A 32-bit signed integer that indicates whether this ObjectId is less than, equal to, or greather than the other.</returns>public int CompareTo(ObjectId other){int result = ((uint)_a).CompareTo((uint)other._a);if (result != 0) { return result; }result = ((uint)_b).CompareTo((uint)other._b);if (result != 0) { return result; }return ((uint)_c).CompareTo((uint)other._c);}/// <summary>/// Compares this ObjectId to another ObjectId./// </summary>/// <param name="rhs">The other ObjectId.</param>/// <returns>True if the two ObjectIds are equal.</returns>public bool Equals(ObjectId rhs){return_a == rhs._a &&_b == rhs._b &&_c == rhs._c;}/// <summary>/// Compares this ObjectId to another object./// </summary>/// <param name="obj">The other object.</param>/// <returns>True if the other object is an ObjectId and equal to this one.</returns>public override bool Equals(object obj){if (obj is ObjectId){return Equals((ObjectId)obj);}else{return false;}}/// <summary>/// Gets the hash code./// </summary>/// <returns>The hash code.</returns>public override int GetHashCode(){int hash = 17;hash = 37 * hash + _a.GetHashCode();hash = 37 * hash + _b.GetHashCode();hash = 37 * hash + _c.GetHashCode();return hash;}/// <summary>/// Converts the ObjectId to a byte array./// </summary>/// <returns>A byte array.</returns>public byte[] ToByteArray(){var bytes = new byte[12];ToByteArray(bytes, 0);return bytes;}/// <summary>/// Converts the ObjectId to a byte array./// </summary>/// <param name="destination">The destination.</param>/// <param name="offset">The offset.</param>public void ToByteArray(byte[] destination, int offset){if (destination == null){throw new ArgumentNullException("destination");}if (offset + 12 > destination.Length){throw new ArgumentException("Not enough room in destination buffer.", "offset");}destination[offset + 0] = (byte)(_a >> 24);destination[offset + 1] = (byte)(_a >> 16);destination[offset + 2] = (byte)(_a >> 8);destination[offset + 3] = (byte)(_a);destination[offset + 4] = (byte)(_b >> 24);destination[offset + 5] = (byte)(_b >> 16);destination[offset + 6] = (byte)(_b >> 8);destination[offset + 7] = (byte)(_b);destination[offset + 8] = (byte)(_c >> 24);destination[offset + 9] = (byte)(_c >> 16);destination[offset + 10] = (byte)(_c >> 8);destination[offset + 11] = (byte)(_c);}/// <summary>/// Returns a string representation of the value./// </summary>/// <returns>A string representation of the value.</returns>public override string ToString(){var c = new char[24];c[0] = BsonUtils.ToHexChar((_a >> 28) & 0x0f);c[1] = BsonUtils.ToHexChar((_a >> 24) & 0x0f);c[2] = BsonUtils.ToHexChar((_a >> 20) & 0x0f);c[3] = BsonUtils.ToHexChar((_a >> 16) & 0x0f);c[4] = BsonUtils.ToHexChar((_a >> 12) & 0x0f);c[5] = BsonUtils.ToHexChar((_a >> 8) & 0x0f);c[6] = BsonUtils.ToHexChar((_a >> 4) & 0x0f);c[7] = BsonUtils.ToHexChar(_a & 0x0f);c[8] = BsonUtils.ToHexChar((_b >> 28) & 0x0f);c[9] = BsonUtils.ToHexChar((_b >> 24) & 0x0f);c[10] = BsonUtils.ToHexChar((_b >> 20) & 0x0f);c[11] = BsonUtils.ToHexChar((_b >> 16) & 0x0f);c[12] = BsonUtils.ToHexChar((_b >> 12) & 0x0f);c[13] = BsonUtils.ToHexChar((_b >> 8) & 0x0f);c[14] = BsonUtils.ToHexChar((_b >> 4) & 0x0f);c[15] = BsonUtils.ToHexChar(_b & 0x0f);c[16] = BsonUtils.ToHexChar((_c >> 28) & 0x0f);c[17] = BsonUtils.ToHexChar((_c >> 24) & 0x0f);c[18] = BsonUtils.ToHexChar((_c >> 20) & 0x0f);c[19] = BsonUtils.ToHexChar((_c >> 16) & 0x0f);c[20] = BsonUtils.ToHexChar((_c >> 12) & 0x0f);c[21] = BsonUtils.ToHexChar((_c >> 8) & 0x0f);c[22] = BsonUtils.ToHexChar((_c >> 4) & 0x0f);c[23] = BsonUtils.ToHexChar(_c & 0x0f);return new string(c);}// explicit IConvertible implementationTypeCode IConvertible.GetTypeCode(){return TypeCode.Object;}bool IConvertible.ToBoolean(IFormatProvider provider){throw new InvalidCastException();}byte IConvertible.ToByte(IFormatProvider provider){throw new InvalidCastException();}char IConvertible.ToChar(IFormatProvider provider){throw new InvalidCastException();}DateTime IConvertible.ToDateTime(IFormatProvider provider){throw new InvalidCastException();}decimal IConvertible.ToDecimal(IFormatProvider provider){throw new InvalidCastException();}double IConvertible.ToDouble(IFormatProvider provider){throw new InvalidCastException();}short IConvertible.ToInt16(IFormatProvider provider){throw new InvalidCastException();}int IConvertible.ToInt32(IFormatProvider provider){throw new InvalidCastException();}long IConvertible.ToInt64(IFormatProvider provider){throw new InvalidCastException();}sbyte IConvertible.ToSByte(IFormatProvider provider){throw new InvalidCastException();}float IConvertible.ToSingle(IFormatProvider provider){throw new InvalidCastException();}string IConvertible.ToString(IFormatProvider provider){return ToString();}object IConvertible.ToType(Type conversionType, IFormatProvider provider){switch (Type.GetTypeCode(conversionType)){case TypeCode.String:return ((IConvertible)this).ToString(provider);case TypeCode.Object:if (conversionType == typeof(object) || conversionType == typeof(ObjectId)){return this;}if (conversionType == typeof(BsonObjectId)){return new BsonObjectId(this);}if (conversionType == typeof(BsonString)){return new BsonString(((IConvertible)this).ToString(provider));}break;}throw new InvalidCastException();}ushort IConvertible.ToUInt16(IFormatProvider provider){throw new InvalidCastException();}uint IConvertible.ToUInt32(IFormatProvider provider){throw new InvalidCastException();}ulong IConvertible.ToUInt64(IFormatProvider provider){throw new InvalidCastException();}}
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