EFCore高級Saas系統下單DbContext如何支持不同數據庫的遷移

前言

隨著系統的不斷開發和迭代默認的efcore功能十分強大，但是隨著Saas系統的引進efcore基于表字段的多租戶模式已經非常完美了，但是基于數據庫的多租戶也是可以用的，但是也存在缺點，缺點就是沒有辦法支持不同數據庫，migration support multi database provider with single dbcontext，本人不才，查詢了一下，官方文檔只說明了dbcontext的遷移如何實現多數據源，但是缺不是單個dbcontext,這個就讓人很頭疼。所以秉著嘗試一下的原則進行了這篇博客的編寫,因為本人只有mmsql和mysql所以這次就用這兩個數據庫來做測試

廣告時間

本人開發了一款efcore的分表分庫讀寫分離組件

https://github.com/dotnetcore/sharding-core

希望有喜歡的小伙伴給我點點star謝謝

那么廢話不多說我們馬上開始migration support multi database provider with single dbcontext

新建項目

1.按裝依賴

2.新建一個User類

[Table(nameof(User))]
public class User{public string UserId { get; set; }public string UserName { get; set; }
}

3.創建DbContext

public class MyDbContext:DbContext
{public DbSet<User> Users { get; set; }public MyDbContext(DbContextOptions<MyDbContext> options):base(options){}

4.StartUp配置

var provider = builder.Configuration.GetValue("Provider", "UnKnown");//Add-Migration InitialCreate -Context MyDbContext -OutputDir Migrations\SqlServer -Args "--provider SqlServer"//Add-Migration InitialCreate -Context MyDbContext -OutputDir Migrations\MySql -Args "--provider MySql"builder.Services.AddDbContext<MyDbContext>(options =>
{_ = provider switch{        "MySql" => options.UseMySql("server=127.0.0.1;port=3306;database=DBMultiDataBase;userid=root;password=L6yBtV6qNENrwBy7;", new MySqlServerVersion(new Version())),        "SqlServer" => options.UseSqlServer("Data Source=localhost;Initial Catalog=DBMultiDataBase;Integrated Security=True;"),_ => throw new Exception($"Unsupported provider: {provider}")};
});

遷移區分數據庫

新建一個遷移命名空間提供者

public interface IMigrationNamespace{        string GetNamespace();}

mysql和sqlserver的實現分別是項目名稱遷移文件夾

public class MySqlMigrationNamespace:IMigrationNamespace{public string GetNamespace(){            return "EFCoreMigrateMultiDatabase.Migrations.MySql";}}public class SqlServerMigrationNamespace:IMigrationNamespace{public string GetNamespace(){            return "EFCoreMigrateMultiDatabase.Migrations.SqlServer";}}

efcore擴展

添加efcore擴展

public class MigrationNamespaceExtension : IDbContextOptionsExtension{public IMigrationNamespace MigrationNamespace { get; }public MigrationNamespaceExtension(IMigrationNamespace migrationNamespace){MigrationNamespace = migrationNamespace;}public void ApplyServices(IServiceCollection services){services.AddSingleton<IMigrationNamespace>(sp => MigrationNamespace);}public void Validate(IDbContextOptions options){}public DbContextOptionsExtensionInfo Info => new MigrationNamespaceExtensionInfo(this);private class MigrationNamespaceExtensionInfo : DbContextOptionsExtensionInfo{private readonly MigrationNamespaceExtension _migrationNamespaceExtension;public MigrationNamespaceExtensionInfo(IDbContextOptionsExtension extension) : base(extension){_migrationNamespaceExtension = (MigrationNamespaceExtension)extension;}public override int GetServiceProviderHashCode() => _migrationNamespaceExtension.MigrationNamespace.GetNamespace().GetHashCode();public override bool ShouldUseSameServiceProvider(DbContextOptionsExtensionInfo other) => true;public override void PopulateDebugInfo(IDictionary<string, string> debugInfo){}public override bool IsDatabaseProvider => false;public override string LogFragment => "MigrationNamespaceExtension";}}

重寫MigrationsAssembly支持多數據庫

public class EFCoreMultiDatabaseMigrationsAssembly: IMigrationsAssembly{public  string MigrationNamespace { get; }private readonly IMigrationsIdGenerator _idGenerator;private readonly IDiagnosticsLogger<DbLoggerCategory.Migrations> _logger;private IReadOnlyDictionary<string, TypeInfo>? _migrations;private ModelSnapshot? _modelSnapshot;private readonly Type _contextType;        /// <summary>///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to///     the same compatibility standards as public APIs. It may be changed or removed without notice in///     any release. You should only use it directly in your code with extreme caution and knowing that///     doing so can result in application failures when updating to a new Entity Framework Core release./// </summary>public EFCoreMultiDatabaseMigrationsAssembly(IMigrationNamespace migrationNamespace,ICurrentDbContext currentContext,IDbContextOptions options,IMigrationsIdGenerator idGenerator,IDiagnosticsLogger<DbLoggerCategory.Migrations> logger){_contextType = currentContext.Context.GetType();var assemblyName = RelationalOptionsExtension.Extract(options)?.MigrationsAssembly;Assembly = assemblyName == null? _contextType.Assembly: Assembly.Load(new AssemblyName(assemblyName));MigrationNamespace = migrationNamespace.GetNamespace();_idGenerator = idGenerator;_logger = logger;}        /// <summary>///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to///     the same compatibility standards as public APIs. It may be changed or removed without notice in///     any release. You should only use it directly in your code with extreme caution and knowing that///     doing so can result in application failures when updating to a new Entity Framework Core release./// </summary>public virtual IReadOnlyDictionary<string, TypeInfo> Migrations{get{IReadOnlyDictionary<string, TypeInfo> Create(){var result = new SortedList<string, TypeInfo>();var items= from t in Assembly.GetConstructibleTypes()where t.IsSubclassOf(typeof(Migration))&& print(t)&& t.Namespace.Equals(MigrationNamespace)&& t.GetCustomAttribute<DbContextAttribute>()?.ContextType == _contextTypelet id = t.GetCustomAttribute<MigrationAttribute>()?.Idorderby idselect (id, t);Console.WriteLine("Migrations:" + items.Count());foreach (var (id, t) in items){                        if (id == null){_logger.MigrationAttributeMissingWarning(t);                            continue;}result.Add(id, t);}                    return result;}                return _migrations ??= Create();}}private bool print(TypeInfo t){Console.WriteLine(MigrationNamespace);Console.WriteLine(t.Namespace);            return true;}        /// <summary>///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to///     the same compatibility standards as public APIs. It may be changed or removed without notice in///     any release. You should only use it directly in your code with extreme caution and knowing that///     doing so can result in application failures when updating to a new Entity Framework Core release./// </summary>public virtual ModelSnapshot? ModelSnapshot=> GetMod();private ModelSnapshot GetMod(){Console.WriteLine("_modelSnapshot:"+ _modelSnapshot);            if (_modelSnapshot == null){Console.WriteLine("_modelSnapshot:null");_modelSnapshot = (from t in Assembly.GetConstructibleTypes()where t.IsSubclassOf(typeof(ModelSnapshot)) && print(t)&& MigrationNamespace.Equals(t?.Namespace)&& t.GetCustomAttribute<DbContextAttribute>()?.ContextType == _contextTypeselect (ModelSnapshot)Activator.CreateInstance(t.AsType())!).FirstOrDefault();Console.WriteLine("_modelSnapshot:" + _modelSnapshot);}            return _modelSnapshot;}        /// <summary>///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to///     the same compatibility standards as public APIs. It may be changed or removed without notice in///     any release. You should only use it directly in your code with extreme caution and knowing that///     doing so can result in application failures when updating to a new Entity Framework Core release./// </summary>public virtual Assembly Assembly { get; }        /// <summary>///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to///     the same compatibility standards as public APIs. It may be changed or removed without notice in///     any release. You should only use it directly in your code with extreme caution and knowing that///     doing so can result in application failures when updating to a new Entity Framework Core release./// </summary>public virtual string? FindMigrationId(string nameOrId)=> Migrations.Keys.Where(_idGenerator.IsValidId(nameOrId)                        // ReSharper disable once ImplicitlyCapturedClosure? id => string.Equals(id, nameOrId, StringComparison.OrdinalIgnoreCase): id => string.Equals(_idGenerator.GetName(id), nameOrId, StringComparison.OrdinalIgnoreCase)).FirstOrDefault();        /// <summary>///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to///     the same compatibility standards as public APIs. It may be changed or removed without notice in///     any release. You should only use it directly in your code with extreme caution and knowing that///     doing so can result in application failures when updating to a new Entity Framework Core release./// </summary>public virtual Migration CreateMigration(TypeInfo migrationClass, string activeProvider){Console.WriteLine(migrationClass.FullName);var migration = (Migration)Activator.CreateInstance(migrationClass.AsType())!;migration.ActiveProvider = activeProvider;            return migration;}}折疊

編寫startup

參考?https://docs.microsoft.com/en-us/ef/core/managing-schemas/migrations/providers?tabs=vs

//Add-Migration InitialCreate -Context MyDbContext -OutputDir Migrations\SqlServer -Args "--provider SqlServer"//Add-Migration InitialCreate -Context MyDbContext -OutputDir Migrations\MySql -Args "--provider MySql"//update-database -Args "--provider MySql"//update-database -Args "--provider SqlServer"builder.Services.AddDbContext<MyDbContext>(options =>
{options.ReplaceService<IMigrationsAssembly, EFCoreMultiDatabaseMigrationsAssembly>();_ = provider switch{        "MySql" => options.UseMySql("server=127.0.0.1;port=3306;database=DBMultiDataBase;userid=root;password=L6yBtV6qNENrwBy7;", new MySqlServerVersion(new Version())).UseMigrationNamespace(new MySqlMigrationNamespace()),        "SqlServer" => options.UseSqlServer("Data Source=localhost;Initial Catalog=DBMultiDataBase;Integrated Security=True;").UseMigrationNamespace(new SqlServerMigrationNamespace()),_ => throw new Exception($"Unsupported provider: {provider}")};
});

到此為止我這邊想我們應該已經實現了把,但是如果我們分別執行兩個遷移命令會導致前一個遷移命令被覆蓋掉,經過一整個下午的debug調試最后發現是因為在遷移腳本生成寫入文件的時候會判斷當前DbContext'的ModelSnapshot,同一個dbcontext生成的文件是一樣的，所以我們這邊有兩個選擇

1.讓生成的文件名不一樣
2.讓ModelSnapshot不進行深度查詢只在當前目錄下處理
這邊選了第二種

public class MyMigrationsScaffolder: MigrationsScaffolder{private readonly Type _contextType;public MyMigrationsScaffolder(MigrationsScaffolderDependencies dependencies) : base(dependencies){_contextType = dependencies.CurrentContext.Context.GetType();}protected override string GetDirectory(string projectDir, string? siblingFileName, string subnamespace){var defaultDirectory = Path.Combine(projectDir, Path.Combine(subnamespace.Split('.')));            if (siblingFileName != null){                if (!siblingFileName.StartsWith(_contextType.Name + "ModelSnapshot.")){var siblingPath = TryGetProjectFile(projectDir, siblingFileName);                    if (siblingPath != null){var lastDirectory = Path.GetDirectoryName(siblingPath)!;                        if (!defaultDirectory.Equals(lastDirectory, StringComparison.OrdinalIgnoreCase)){Dependencies.OperationReporter.WriteVerbose(DesignStrings.ReusingNamespace(siblingFileName));                            return lastDirectory;}}}}            return defaultDirectory;}}

添加designservices

public class MyMigrationDesignTimeServices: IDesignTimeServices{public void ConfigureDesignTimeServices(IServiceCollection serviceCollection){serviceCollection.AddSingleton<IMigrationsScaffolder, MyMigrationsScaffolder>();}}