如何从多个不同NuGet包运行EF Core迁移？

要实现主项目+多插件的迁移支持，核心是让EF Core能够扫描并加载多个程序集里的迁移文件，以下是具体实现步骤：

1. 自定义迁移程序集聚合类 #

创建CompositeMigrationsAssembly类，实现EF Core的IMigrationsAssembly接口，用于聚合主项目和所有插件的迁移：

using Microsoft.EntityFrameworkCore.Migrations;
using System.Reflection;

public class CompositeMigrationsAssembly : IMigrationsAssembly
{
    private readonly IMigrationsAssembly _innerAssembly;
    private readonly IEnumerable<Assembly> _additionalAssemblies;

    public CompositeMigrationsAssembly(
        IMigrationsAssembly innerAssembly,
        IEnumerable<Assembly> additionalAssemblies)
    {
        _innerAssembly = innerAssembly;
        _additionalAssemblies = additionalAssemblies;
    }

    public string MigrationsNamespace => _innerAssembly.MigrationsNamespace;

    public Assembly Assembly => _innerAssembly.Assembly;

    public IReadOnlyDictionary<string, Type> Migrations => GetAllMigrations();

    public Migration GetMigration(string migrationId)
    {
        var migration = _innerAssembly.Migrations.TryGetValue(migrationId, out var type) 
            ? (Migration)Activator.CreateInstance(type) 
            : null;

        if (migration == null)
        {
            foreach (var assembly in _additionalAssemblies)
            {
                var migrationsInAssembly = assembly.GetTypes()
                    .Where(t => typeof(Migration).IsAssignableFrom(t) && !t.IsAbstract)
                    .ToDictionary(t => t.GetCustomAttribute<MigrationAttribute>()!.Id);

                if (migrationsInAssembly.TryGetValue(migrationId, out var migrationType))
                {
                    migration = (Migration)Activator.CreateInstance(migrationType);
                    break;
                }
            }
        }

        return migration ?? throw new InvalidOperationException($"Migration {migrationId} not found.");
    }

    public Type GetMigrationType(string migrationId)
    {
        var type = _innerAssembly.Migrations.TryGetValue(migrationId, out var t) ? t : null;

        if (type == null)
        {
            foreach (var assembly in _additionalAssemblies)
            {
                var migrationsInAssembly = assembly.GetTypes()
                    .Where(t => typeof(Migration).IsAssignableFrom(t) && !t.IsAbstract)
                    .ToDictionary(t => t.GetCustomAttribute<MigrationAttribute>()!.Id);

                if (migrationsInAssembly.TryGetValue(migrationId, out var migrationType))
                {
                    type = migrationType;
                    break;
                }
            }
        }

        return type ?? throw new InvalidOperationException($"Migration type {migrationId} not found.");
    }

    private IReadOnlyDictionary<string, Type> GetAllMigrations()
    {
        var allMigrations = new Dictionary<string, Type>(_innerAssembly.Migrations);

        foreach (var assembly in _additionalAssemblies)
        {
            var migrationsInAssembly = assembly.GetTypes()
                .Where(t => typeof(Migration).IsAssignableFrom(t) && !t.IsAbstract)
                .Select(t => new { Id = t.GetCustomAttribute<MigrationAttribute>()!.Id, Type = t });

            foreach (var migration in migrationsInAssembly)
            {
                if (!allMigrations.ContainsKey(migration.Id))
                {
                    allMigrations.Add(migration.Id, migration.Type);
                }
            }
        }

        return allMigrations;
    }
}

2. 配置DbContext并替换迁移程序集服务 #

在Program.cs（或Startup.cs）中，先正常注册DbContext，再替换默认的IMigrationsAssembly为自定义的聚合实现：

// 收集所有需要包含的迁移程序集：主项目程序集 + 所有插件程序集
var migrationAssemblies = new List<Assembly>
{
    typeof(MyDbContext).Assembly, // 主项目的程序集
    // 添加已加载的插件程序集，比如你启动时获取到的pluginAssemblies集合
    ...pluginAssemblies
};

// 注册DbContext，无需指定单个MigrationsAssembly
builder.Services.AddDbContext<MyDbContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));

// 替换IMigrationsAssembly服务，实现多程序集迁移加载
builder.Services.AddScoped<IMigrationsAssembly>(sp =>
{
    var defaultMigrationsAssembly = sp.GetRequiredService<IMigrationsAssembly>();
    // 传入主项目之外的其他迁移程序集（插件程序集）
    return new CompositeMigrationsAssembly(defaultMigrationsAssembly, migrationAssemblies.Skip(1));
});

3. 生成各模块的迁移 #

使用EF Core CLI分别为主项目和每个插件生成迁移：

• 生成主项目迁移：

dotnet ef migrations add AddMainProjectEntities --project ./MainProject --startup-project ./MainProject

• 生成某插件的迁移（以PluginA为例）：

dotnet ef migrations add AddPluginAEntities --project ./Plugins/PluginA --startup-project ./MainProject

4. 运行所有迁移 #

直接在主项目执行数据库更新命令，自定义的CompositeMigrationsAssembly会自动加载所有程序集的迁移并执行：

dotnet ef database update --startup-project ./MainProject

注意事项 #

• 确保所有迁移的ID唯一：EF Core自动生成的迁移ID包含时间戳，只要不手动修改，不会出现重复问题。
• 插件项目需引用EF Core相关包：确保插件项目能正常生成迁移文件。
• 设计时访问DbContext：生成插件迁移时，需通过--startup-project指定主项目，确保EF Core能找到DbContext的配置。

内容的提问来源于stack exchange，提问作者YodasMyDad