EfCore实现全自动化迁移数据库结构，非执行命令。达到运行时自动迁移，且数据库有数据结构的记录。
主题：Asp.netcore Code First +DDD学习笔记
目录：
【一】 CodeFirst+DDD项目结构的构建
【二】Asp.Netcore使用Panda.DynamicWebApi来进行Controller解耦
【三】Asp.NetCore使用Efcore+Mysql实现CodeFirst
【四】EfCore实现全自动化迁移
案例代码下载点击
在Efcore官网上说的运行时迁移是你执行完成Add-Migration后在代码运行时执行myDbContext.Database.Migrate();数据库的数据结构会被更改，但是这个并不是我们所需要。我不想执行Add-Migration我想实现全自动化的方式。我们要实现自动化数据结构迁移，并在迁移时，非数据错误的字段修改和调整不会删除数据。就和执行命令达到的效果是一样的。
寻找Efcore内的方法发现：
在Efcore官方里面有如下三个方法：
var modelDiffer = dbContext.GetInfrastructure().GetService<IMigrationsModelDiffer>();modelDiffer.HasDifferences(lastModel, dbContext.Model)；//这个方法返回值是true或者false，这个可以比较老版本的model和当前版本的model是否出现更改。var upOperations = modelDiffer.GetDifferences(lastModel, dbContext.Model);//这个方法返回的迁移的操作对象。dbContext.GetInfrastructure() .GetRequiredService<IMigrationsSqlGenerator>().Generate(upOperations, dbContext.Model).ToList()；//这个方法是根据迁移对象和当前的model生成迁移sql脚本。根据以上三个方法我们可以把迁移做成自动化，首先我们要知道是否出现版本修改，我们要先知道老版本的model是什么样子的，这时候我们需要在每次迁移完成后，把model存到数据库即可。
每次我们从数据库拿出来最后一次的model使用HasDifferences方法和现在的model做比较，出现需要修改的时候我们使用GetDifferences方法获取迁移对象，然后根据迁移对象使用Generate方法来生成sql脚本，最后用efcore执行sql脚本即可。
如何把model存到数据库，并在从数据库取出后能还原成model用来最比较呢。我第一个想到的是序列化，于是我进行了尝试，发现该dbContext.Model不允许进行序列化。后来看到一大佬说：每次迁移生成的快照实际上是动态生成的类，所以要用动态编辑机制CSharpCompilation和CSharpCompilationOptions。大佬的文章链接：https://blog.csdn.net/weixin_38687913/article/details/81122169，于是得出如下解决方案
一. 给domain安装nuget包
Microsoft.CodeAnalysis.Common 版本选择2.8
二.创建保存数据库版本的实体类
在Domain的Domains创建MigrationLogs文件夹，并在该文件夹里面创建MigrationLog类，具体代码如下：
using EfCoreRepository.EfModelAttributes;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Text;namespace Domain.MigrationLogs
{[EfModel]public class MigrationLog{[Key]public int Id { get; set; }public string SnapshotDefine { get; set; }public DateTime MigrationTime { get; set; }}
}
三.修改efcontent如下
using Domain.MigrationLogs;
using EfCoreRepository;
using EfCoreRepository.EfModelAttributes;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;
using Microsoft.EntityFrameworkCore.Design.Internal;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Metadata;
using Microsoft.EntityFrameworkCore.Migrations;
using Microsoft.EntityFrameworkCore.Migrations.Design;
using Microsoft.EntityFrameworkCore.Migrations.Operations;
using Microsoft.Extensions.DependencyInjection;
using MySql.Data.MySqlClient;
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Common;
using System.IO;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Threading.Tasks;namespace Domain.EfCoreContent
{public class EfContent : DbContext{public DbContextOptions<EfContent> dbContextOptions { get; set; }public EfContent(DbContextOptions<EfContent> options) : base(options){dbContextOptions = options;}/// <summary>/// 创建实体/// </summary>/// <param name="modelBuilder"></param>protected override void OnModelCreating(ModelBuilder modelBuilder){modelBuilder.AddEntityConfigurationsFromAssembly<EfModelAttribute>(Assembly.GetExecutingAssembly());base.OnModelCreating(modelBuilder);}/// <summary>/// 扩展查询/// </summary>/// <typeparam name="T"></typeparam>/// <param name="predicate"></param>/// <returns></returns>public IQueryable<T> Where<T>(Expression<Func<T, bool>> predicate) where T : class{return base.Set<T>().Where(predicate);}}/// <summary>/// efcore扩展sql查询/// </summary>public static class EntityFrameworkCoreExtensions{/// <summary>/// 执行sql返回datatable/// </summary>/// <param name="efcontent"></param>/// <param name="sql"></param>/// <param name="commandParameters"></param>/// <returns></returns>public static DataTable SqlQuery(this EfContent efcontent, string sql, params object[] commandParameters){var dt = new DataTable();using (var connection = efcontent.Database.GetDbConnection()){using (var cmd = connection.CreateCommand()){efcontent.Database.OpenConnection();cmd.CommandText = sql;if (commandParameters != null && commandParameters.Length > 0)cmd.Parameters.AddRange(commandParameters);using (var reader = cmd.ExecuteReader()){dt.Load(reader);}}}return dt;}/// <summary>/// 执行多条sql/// </summary>/// <param name="efcontent"></param>/// <param name="sqlList"></param>public static int ExecuteListSqlCommand(this EfContent efcontent,List<string> sqlList){int retunInt = 0;try{using (var trans = efcontent.Database.BeginTransaction()){sqlList.ForEach(cmd => retunInt+= efcontent.Database.ExecuteSqlCommand(cmd));efcontent.Database.CommitTransaction();}}catch (DbException ex){try{efcontent.Database.RollbackTransaction();}catch (DbException){}}return retunInt;}/// <summary>/// 执行sql返回list/// </summary>/// <typeparam name="T"></typeparam>/// <param name="efcontent"></param>/// <param name="sql"></param>/// <param name="parameters"></param>/// <returns></returns>public static List<T> SqlQuery<T>(this EfContent efcontent, string sql, params object[] parameters) where T : class, new(){var dt = SqlQuery(efcontent, sql, parameters);return dt.ToList<T>();}/// <summary>/// datatable转list/// </summary>/// <typeparam name="T"></typeparam>/// <param name="dt"></param>/// <returns></returns>public static List<T> ToList<T>(this DataTable dt) where T : class, new(){var propertyInfos = typeof(T).GetProperties();var list = new List<T>();foreach (DataRow row in dt.Rows){var t = new T();foreach (PropertyInfo p in propertyInfos){if (dt.Columns.IndexOf(p.Name) != -1 && row[p.Name] != DBNull.Value)p.SetValue(t, row[p.Name], null);}list.Add(t);}return list;}}/// <summary>/// 给efcontent扩展自动处理数据库版本的方法/// </summary>public static class EfCoreMigration{/// <summary>/// 给EfContent添加的更新数据库结构的方法/// </summary>public static void RunUpdateDataBaseEntity(this EfContent _dbContext){// 创建一个DbContext，具体方法怎样都行IModel lastModel = null;try{// 读取迁移记录，把快照还原会modelvar lastMigration = _dbContext.Set<MigrationLog>().OrderByDescending(e => e.Id) .FirstOrDefault();lastModel = lastMigration == null ? null : (CreateModelSnapshot(lastMigration.SnapshotDefine)?.Model);}catch (DbException) { }var modelDiffer = _dbContext.Database.GetService<IMigrationsModelDiffer>();//判断是否有更改if (modelDiffer.HasDifferences(lastModel, _dbContext.Model)){// 用 IMigrationsModelDiffer 的 GetDifferences 方法获取迁移的操作对象var upOperations = modelDiffer.GetDifferences(lastModel, _dbContext.Model);//执行迁移Migrationing(upOperations, _dbContext);// 生成新的快照，存起来var snapshotCode = new DesignTimeServicesBuilder(typeof(EfContent).Assembly, Assembly.GetEntryAssembly(), new OperationReporter(new OperationReportHandler()), new string[0]).Build((DbContext)_dbContext).GetService<IMigrationsCodeGenerator>().GenerateSnapshot("ApiHost.Migrations", typeof(EfContent), "EfContentModelSnapshot", _dbContext.Model);//modelSnapshotNamespace：给动态生成类添加nameplace（必须和当前代码所在的命名控件下或者一样）modelSnapshotName：动态生成类的名称_dbContext.Set<MigrationLog>().Add(new MigrationLog(){SnapshotDefine = snapshotCode,MigrationTime = DateTime.Now});_dbContext.SaveChanges();}}/// <summary>/// 迁移数据库结构/// </summary>/// <param name="upOperations"></param>/// <param name="_dbContext"></param>private static void Migrationing(IReadOnlyList<MigrationOperation> upOperations,EfContent _dbContext){List<string> sqlChangeColumNameList = new List<string>();List<MigrationOperation> list = new List<MigrationOperation>();//执行迁移列名修改foreach (var upOperation in upOperations){if (upOperation is RenameColumnOperation){sqlChangeColumNameList.Add(RenameColumnOperationToSql(upOperation as RenameColumnOperation, _dbContext));}else{list.Add(upOperation);}}int columChangeCount = _dbContext.ExecuteListSqlCommand(sqlChangeColumNameList); //处理剩余迁移if (list.Count > 0){//通过 IMigrationsSqlGenerator 将操作迁移操作对象生成迁移的sql脚本，并执行var sqlList = _dbContext.Database.GetService<IMigrationsSqlGenerator>().Generate(list, _dbContext.Model).Select(p=>p.CommandText).ToList();int changeCount= _dbContext.ExecuteListSqlCommand(sqlList);}}/// <summary>/// 把RenameColumnOperation该字段转换成sql/// </summary>/// <param name="renameColumnOperation"></param>/// <returns></returns>private static string RenameColumnOperationToSql(RenameColumnOperation renameColumnOperation, EfContent _dbContext){string column_type = string.Empty;string sql = "select column_type from information_schema.columns where table_name='" + (renameColumnOperation as RenameColumnOperation).Table + "' and column_name='" + (renameColumnOperation as RenameColumnOperation).Name + "'";var dataTable = _dbContext.SqlQuery(sql);if (dataTable != null && dataTable.Rows.Count > 0){column_type = dataTable.Rows[0].ItemArray[0].ToString();}return "alter table " + (renameColumnOperation as RenameColumnOperation).Table + " change column " + (renameColumnOperation as RenameColumnOperation).Name + " " + (renameColumnOperation as RenameColumnOperation).NewName + " " + column_type + " ;";}/// <summary>/// 把实体的string转成该对象/// </summary>/// <param name="codedefine"></param>/// <returns></returns>private static ModelSnapshot CreateModelSnapshot(string codedefine){// 生成快照，需要存到数据库中供更新版本用var references = typeof(EfContent).Assembly.GetReferencedAssemblies().Select(e => MetadataReference.CreateFromFile(Assembly.Load(e).Location)).Union(new MetadataReference[]{MetadataReference.CreateFromFile(Assembly.Load("netstandard").Location),MetadataReference.CreateFromFile(Assembly.Load("System.Runtime").Location),MetadataReference.CreateFromFile(typeof(Object).Assembly.Location),MetadataReference.CreateFromFile(typeof(EfContent).Assembly.Location)});var compilation = CSharpCompilation.Create("ApiHost.Migrations")//assemblyName：给动态生成类添加nameplace（必须和当前代码所在的命名控件下或者一样）和生成快照时要保持一直.WithOptions(new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary)).AddReferences(references).AddSyntaxTrees(SyntaxFactory.ParseSyntaxTree(codedefine));using (var stream = new MemoryStream()){var compileResult = compilation.Emit(stream);return compileResult.Success? Assembly.Load(stream.GetBuffer()).CreateInstance("ApiHost.Migrations.EfContentModelSnapshot") as ModelSnapshot //typeName即生成的快照时设置的modelSnapshotNamespace+modelSnapshotName（nameplace+动态生成类的名称）: null;}}}
}
四.在Api项目内调用该静态扩展方法，修改Startup的Configure如下：
public void Configure(IApplicationBuilder app, IHostingEnvironment env, IServiceProvider serviceProvider){//使用跨越配置app.UseCors();//使用SwaggerApi自动生成器app.UseSwagger();//使用SwaggerApi自动生成器的Ui界面app.UseSwaggerUI(option =>{option.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");});using (var scope = serviceProvider.CreateScope()){var efContent = scope.ServiceProvider.GetRequiredService<EfContent>();efContent.RunUpdateDataBaseEntity();}//if (env.IsDevelopment())//{// app.UseDeveloperExceptionPage();//}//else//{// // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.// app.UseHsts();//}//app.UseHttpsRedirection();app.UseMvc();}到这里，每次启动后数据库的结构会自动同步，根据测试和手动用命令执行的过程基本一致。执行后会发现数据库里面版本表里面会保存每次修改的model代码如下：
具体内容就是真实的代码，和手动用命令创建的
这个类的代码一样
如下：
到这里。efcore全自动迁移全部完成。
github地址：https://github.com/houliren/Asp.netcore-Code-First-DDD