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.Driver
2、搜索Nuget手动安装
调用生成主键ObjectId
var primarykeyId = ObjectId.GenerateNewId();
//输出：641c54b2e674000035001dc2
mongo-csharp-driver ObjectId详解
关于ObjectId的生成原理大家阅读如下源码即可。
/* 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 { ////// Represents an ObjectId (see also BsonObjectId). /// #if NET45 [Serializable] #endif public struct ObjectId : IComparable , IEquatable , IConvertible { // private static fields private 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 fields private readonly int _a; private readonly int _b; private readonly int _c; // constructors /// /// Initializes a new instance of the ObjectId class. /// /// The bytes. 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); } /// /// Initializes a new instance of the ObjectId class. /// /// The bytes. /// The index into the byte array where the ObjectId starts. internal ObjectId(byte[] bytes, int index) { FromByteArray(bytes, index, out _a, out _b, out _c); } /// /// Initializes a new instance of the ObjectId class. /// /// The timestamp (expressed as a DateTime). /// The machine hash. /// The PID. /// The increment. public ObjectId(DateTime timestamp, int machine, short pid, int increment) : this(GetTimestampFromDateTime(timestamp), machine, pid, increment) { } /// /// Initializes a new instance of the ObjectId class. /// /// The timestamp. /// The machine hash. /// The PID. /// The increment. 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; } /// /// Initializes a new instance of the ObjectId class. /// /// The value. 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 /// /// Gets an instance of ObjectId where the value is empty. /// public static ObjectId Empty { get { return __emptyInstance; } } // public properties /// /// Gets the timestamp. /// public int Timestamp { get { return _a; } } /// /// Gets the machine. /// public int Machine { get { return (_b >> 8) & 0xffffff; } } /// /// Gets the PID. /// public short Pid { get { return (short)(((_b << 8) & 0xff00) | ((_c >> 24) & 0x00ff)); } } /// /// Gets the increment. /// public int Increment { get { return _c & 0xffffff; } } /// /// Gets the creation time (derived from the timestamp). /// public DateTime CreationTime { get { return BsonConstants.UnixEpoch.AddSeconds(Timestamp); } } // public operators /// /// Compares two ObjectIds. /// /// The first ObjectId. /// The other ObjectId /// True if the first ObjectId is less than the second ObjectId. public static bool operator <(ObjectId lhs, ObjectId rhs) { return lhs.CompareTo(rhs) < 0; } /// /// Compares two ObjectIds. /// /// The first ObjectId. /// The other ObjectId /// True if the first ObjectId is less than or equal to the second ObjectId. public static bool operator <=(ObjectId lhs, ObjectId rhs) { return lhs.CompareTo(rhs) <= 0; } /// /// Compares two ObjectIds. /// /// The first ObjectId. /// The other ObjectId. /// True if the two ObjectIds are equal. public static bool operator ==(ObjectId lhs, ObjectId rhs) { return lhs.Equals(rhs); } /// /// Compares two ObjectIds. /// /// The first ObjectId. /// The other ObjectId. /// True if the two ObjectIds are not equal. public static bool operator !=(ObjectId lhs, ObjectId rhs) { return !(lhs == rhs); } /// /// Compares two ObjectIds. /// /// The first ObjectId. /// The other ObjectId /// True if the first ObjectId is greather than or equal to the second ObjectId. public static bool operator >=(ObjectId lhs, ObjectId rhs) { return lhs.CompareTo(rhs) >= 0; } /// /// Compares two ObjectIds. /// /// The first ObjectId. /// The other ObjectId /// True if the first ObjectId is greather than the second ObjectId. public static bool operator >(ObjectId lhs, ObjectId rhs) { return lhs.CompareTo(rhs) > 0; } // public static methods /// /// Generates a new ObjectId with a unique value. /// /// An ObjectId. public static ObjectId GenerateNewId() { return GenerateNewId(GetTimestampFromDateTime(DateTime.UtcNow)); } /// /// Generates a new ObjectId with a unique value (with the timestamp component based on a given DateTime). /// /// The timestamp component (expressed as a DateTime). /// An ObjectId. public static ObjectId GenerateNewId(DateTime timestamp) { return GenerateNewId(GetTimestampFromDateTime(timestamp)); } /// /// Generates a new ObjectId with a unique value (with the given timestamp). /// /// The timestamp component. /// An ObjectId. public static ObjectId GenerateNewId(int timestamp) { int increment = Interlocked.Increment(ref __staticIncrement) & 0x00ffffff; // only use low order 3 bytes return new ObjectId(timestamp, __staticMachine, __staticPid, increment); } /// /// Packs the components of an ObjectId into a byte array. /// /// The timestamp. /// The machine hash. /// The PID. /// The increment. /// A byte array. 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; } /// /// Parses a string and creates a new ObjectId. /// /// The string value. /// A ObjectId. 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); } } /// /// Tries to parse a string and create a new ObjectId. /// /// The string value. /// The new ObjectId. /// True if the string was parsed successfully. public static bool TryParse(string s, out ObjectId objectId) { // don't throw ArgumentNullException if s is null if (s != null && s.Length == 24) { byte[] bytes; if (BsonUtils.TryParseHexString(s, out bytes)) { objectId = new ObjectId(bytes); return true; } } objectId = default(ObjectId); return false; } /// /// Unpacks a byte array into the components of an ObjectId. /// /// A byte array. /// The timestamp. /// The machine hash. /// The PID. /// The increment. 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 methods private static int GetAppDomainId() { #if NETSTANDARD1_5 || NETSTANDARD1_6 return 1; #else return AppDomain.CurrentDomain.Id; #endif } /// /// 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. /// [MethodImpl(MethodImplOptions.NoInlining)] private static int GetCurrentProcessId() { return Process.GetCurrentProcess().Id; } private static int GetMachineHash() { // use instead of Dns.HostName so it will work offline var 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 /// /// Compares this ObjectId to another ObjectId. /// /// The other ObjectId. /// A 32-bit signed integer that indicates whether this ObjectId is less than, equal to, or greather than the other. 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); } /// /// Compares this ObjectId to another ObjectId. /// /// The other ObjectId. /// True if the two ObjectIds are equal. public bool Equals(ObjectId rhs) { return _a == rhs._a && _b == rhs._b && _c == rhs._c; } /// /// Compares this ObjectId to another object. /// /// The other object. /// True if the other object is an ObjectId and equal to this one. public override bool Equals(object obj) { if (obj is ObjectId) { return Equals((ObjectId)obj); } else { return false; } } /// /// Gets the hash code. /// /// The hash code. public override int GetHashCode() { int hash = 17; hash = 37 * hash + _a.GetHashCode(); hash = 37 * hash + _b.GetHashCode(); hash = 37 * hash + _c.GetHashCode(); return hash; } /// /// Converts the ObjectId to a byte array. /// /// A byte array. public byte[] ToByteArray() { var bytes = new byte[12]; ToByteArray(bytes, 0); return bytes; } /// /// Converts the ObjectId to a byte array. /// /// The destination. /// The offset. 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); } /// /// Returns a string representation of the value. /// /// A string representation of the value. 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 implementation TypeCode 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(); } } }