EF Core 實現讀寫分離的最佳方案
- 2019 年 10 月 6 日
- 筆記
前言
公司之前使用Ado.net和Dapper進行數據訪問層的操作, 進行讀寫分離也比較簡單, 只要使用對應的資料庫連接字元串即可. 而最近要遷移到新系統中,新系統使用.net core和EF Core進行數據訪問. 所以趁著國慶假期拿出一兩天時間研究了一下如何EF Core進行讀寫分離.
思路
根據園子里的Jeffcky大神的部落格, 參考
EntityFramework Core進行讀寫分離最佳實踐方式，了解一下（一）？
EntityFramework Core進行讀寫分離最佳實踐方式，了解一下（二）？
最簡單的思路就是使用手動切換EF Core上下文的連接, 即context.Database.GetDbConnection().ConnectionString = "xxx", 但必須要先創建上下文, 再關閉之前的連接, 才能進行切換
另一種方式是通過監聽Diagnostic來將進行查詢的sql切換到從庫執行, 這種方式雖然可以實現無感知的切換操作, 但不能滿足公司的業務需求. 在後台管理或其他對數據實時性要求比較高的項目里,查詢操作也都應該走主庫,而這種方式卻會切換到從庫去. 另一方面就是假若公司的庫比較多,每種業務都對應了一個庫, 每個庫都對應了一種DbContext, 這種情況下, 要實現自動切換就變得很複雜了.
上面的兩種方式都是從切換資料庫連接入手,但是頻繁的切換資料庫連接勢必會對性能造成影響. 我認為最理想的方式是要避免資料庫連接的切換, 且能夠適應多DbContext的情況, 在創建上下文實例時,就指定好是訪問主庫還是從庫, 而不是在後期再進行資料庫切換. 因此, 在上下文實例化時,就傳入相應的資料庫連接字元串, 這樣一來DbContext的創建就需要交由我們自己來進行, 就不是由DI容器進行創建了. 同時倉儲應該區分為只讀和可讀可寫兩種,以防止其他人對從庫進行寫操作.
實現
public interface IReadOnlyRepository<TEntity, TKey> where TEntity : class, IEntity<TKey> where TKey : IEquatable<TKey> {} public interface IRepository<TEntity, TKey> : IReadOnlyRepository<TEntity, TKey> where TEntity : class, IEntity<TKey> where TKey : IEquatable<TKey> {}IReadOnlyRepository介面是只讀倉儲介面,提供查詢相關方法,IRepository介面是可讀可寫倉儲介面,提供增刪查改等方法, 介面的實現就那些東西這裡就省略了.
public interface IRepositoryFactory { IRepository<TEntity, TKey> GetRepository<TEntity, TKey>(IUnitOfWork unitOfWork) where TEntity : class, IEntity<TKey> where TKey : IEquatable<TKey>; IReadOnlyRepository<TEntity, TKey> GetReadOnlyRepository<TEntity, TKey>(IUnitOfWork unitOfWork) where TEntity : class, IEntity<TKey> where TKey : IEquatable<TKey>; } public class RepositoryFactory : IRepositoryFactory { public RepositoryFactory() { } public IRepository<TEntity, TKey> GetRepository<TEntity, TKey>(IUnitOfWork unitOfWork) where TEntity : class, IEntity<TKey> where TKey : IEquatable<TKey> { return new Repository<TEntity, TKey>(unitOfWork); } public IReadOnlyRepository<TEntity, TKey> GetReadOnlyRepository<TEntity, TKey>(IUnitOfWork unitOfWork) where TEntity : class, IEntity<TKey> where TKey : IEquatable<TKey> { return new ReadOnlyRepository<TEntity, TKey>(unitOfWork); } }RepositoryFactory提供倉儲對象的實例化
public interface IUnitOfWork : IDisposable { public DbContext DbContext { get; } /// <summary> /// 獲取只讀倉儲對象 /// </summary> IReadOnlyRepository<TEntity, TKey> GetReadOnlyRepository<TEntity, TKey>() where TEntity : class, IEntity<TKey> where TKey : IEquatable<TKey>; /// <summary> /// 獲取倉儲對象 /// </summary> IRepository<TEntity, TKey> GetRepository<TEntity, TKey>() where TEntity : class, IEntity<TKey> where TKey : IEquatable<TKey>; int SaveChanges(); Task<int> SaveChangesAsync(CancellationToken cancelToken = default); } public class UnitOfWork : IUnitOfWork { private readonly IServiceProvider _serviceProvider; private readonly DbContext _dbContext; private readonly IRepositoryFactory _repositoryFactory; private bool _disposed; public UnitOfWork(IServiceProvider serviceProvider, DbContext context) { Check.NotNull(serviceProvider, nameof(serviceProvider)); _serviceProvider = serviceProvider; _dbContext = context; _repositoryFactory = serviceProvider.GetRequiredService<IRepositoryFactory>(); } public DbContext DbContext { get => _dbContext; } public IReadOnlyRepository<TEntity, TKey> GetReadOnlyRepository<TEntity, TKey>() where TEntity : class, IEntity<TKey> where TKey : IEquatable<TKey> { return _repositoryFactory.GetReadOnlyRepository<TEntity, TKey>(this); } public IRepository<TEntity, TKey> GetRepository<TEntity, TKey>() where TEntity : class, IEntity<TKey> where TKey : IEquatable<TKey> { return _repositoryFactory.GetRepository<TEntity, TKey>(this); } public void Dispose() { if (_disposed) { return; } _dbContext?.Dispose(); _disposed = true; } // 其他略 } /// <summary> /// 資料庫提供者介面 /// </summary> public interface IDbProvider : IDisposable { /// <summary> /// 根據上下文類型及資料庫名稱獲取UnitOfWork對象, dbName為null時默認為第一個資料庫名稱 /// </summary> IUnitOfWork GetUnitOfWork(Type dbContextType, string dbName = null); }IDbProvider 介面, 根據上下文類型和配置文件中的資料庫連接字元串名稱創建IUnitOfWork, 在DI中的生命周期是Scoped,在銷毀的同時會銷毀資料庫上下文對象, 下面是它的實現, 為了提高性能使用了Expression來代替反射.
public class DbProvider : IDbProvider { private readonly IServiceProvider _serviceProvider; private readonly ConcurrentDictionary<string, IUnitOfWork> _works = new ConcurrentDictionary<string, IUnitOfWork>(); private static ConcurrentDictionary<Type, Func<IServiceProvider, DbContextOptions, DbContext>> _expressionFactoryDict = new ConcurrentDictionary<Type, Func<IServiceProvider, DbContextOptions, DbContext>>(); public DbProvider(IServiceProvider serviceProvider) { _serviceProvider = serviceProvider; } public IUnitOfWork GetUnitOfWork(Type dbContextType, string dbName = null) { var key = string.Format("{0}${1}$", dbName, dbContextType.FullName); IUnitOfWork unitOfWork; if (_works.TryGetValue(key, out unitOfWork)) { return unitOfWork; } else { DbContext dbContext; var dbConnectionOptionsMap = _serviceProvider.GetRequiredService<IOptions<FxOptions>>().Value.DbConnections; if (dbConnectionOptionsMap == null || dbConnectionOptionsMap.Count <= 0) { throw new Exception("無法獲取資料庫配置"); } DbConnectionOptions dbConnectionOptions = dbName == null ? dbConnectionOptionsMap.First().Value : dbConnectionOptionsMap[dbName]; var builderOptions = _serviceProvider.GetServices<DbContextOptionsBuilderOptions>() ?.Where(d => (d.DbName == null || d.DbName == dbName) && (d.DbContextType == null || d.DbContextType == dbContextType)) ?.OrderByDescending(d => d.DbName) ?.OrderByDescending(d => d.DbContextType); if (builderOptions == null || !builderOptions.Any()) { throw new Exception("無法獲取匹配的DbContextOptionsBuilder"); } var dbUser = _serviceProvider.GetServices<IDbContextOptionsBuilderUser>()?.FirstOrDefault(u => u.Type == dbConnectionOptions.DatabaseType); if (dbUser == null) { throw new Exception($"無法解析類型為「{dbConnectionOptions.DatabaseType}」的 {typeof(IDbContextOptionsBuilderUser).FullName} 實例"); } var dbContextOptions = dbUser.Use(builderOptions.First().Builder, dbConnectionOptions.ConnectionString).Options; if (_expressionFactoryDict.TryGetValue(dbContextType, out Func<IServiceProvider, DbContextOptions, DbContext> factory)) { dbContext = factory(_serviceProvider, dbContextOptions); } else { // 使用Expression創建DbContext var constructorMethod = dbContextType.GetConstructors() .Where(c => c.IsPublic && !c.IsAbstract && !c.IsStatic) .OrderByDescending(c => c.GetParameters().Length) .FirstOrDefault(); if (constructorMethod == null) { throw new Exception("無法獲取有效的上下文構造器"); } var dbContextOptionsBuilderType = typeof(DbContextOptionsBuilder<>); var dbContextOptionsType = typeof(DbContextOptions); var dbContextOptionsGenericType = typeof(DbContextOptions<>); var serviceProviderType = typeof(IServiceProvider); var getServiceMethod = serviceProviderType.GetMethod("GetService"); var lambdaParameterExpressions = new ParameterExpression[2]; lambdaParameterExpressions[0] = (Expression.Parameter(serviceProviderType, "serviceProvider")); lambdaParameterExpressions[1] = (Expression.Parameter(dbContextOptionsType, "dbContextOptions")); var paramTypes = constructorMethod.GetParameters(); var argumentExpressions = new Expression[paramTypes.Length]; for (int i = 0; i < paramTypes.Length; i++) { var pType = paramTypes[i]; if (pType.ParameterType == dbContextOptionsType || (pType.ParameterType.IsGenericType && pType.ParameterType.GetGenericTypeDefinition() == dbContextOptionsGenericType)) { argumentExpressions[i] = Expression.Convert(lambdaParameterExpressions[1], pType.ParameterType); } else if (pType.ParameterType == serviceProviderType) { argumentExpressions[i] = lambdaParameterExpressions[0]; } else { argumentExpressions[i] = Expression.Call(lambdaParameterExpressions[0], getServiceMethod); } } factory = Expression .Lambda<Func<IServiceProvider, DbContextOptions, DbContext>>( Expression.Convert(Expression.New(constructorMethod, argumentExpressions), typeof(DbContext)), lambdaParameterExpressions.AsEnumerable()) .Compile(); _expressionFactoryDict.TryAdd(dbContextType, factory); dbContext = factory(_serviceProvider, dbContextOptions); } var unitOfWorkFactory = _serviceProvider.GetRequiredService<IUnitOfWorkFactory>(); unitOfWork = unitOfWorkFactory.GetUnitOfWork(_serviceProvider, dbContext); _works.TryAdd(key, unitOfWork); return unitOfWork; } } public void Dispose() { if (_works != null && _works.Count > 0) { foreach (var unitOfWork in _works.Values) unitOfWork.Dispose(); _works.Clear(); } } } public static class DbProviderExtensions { public static IUnitOfWork GetUnitOfWork<TDbContext>(this IDbProvider provider, string dbName = null) { if (provider == null) return null; return provider.GetUnitOfWork(typeof(TDbContext), dbName); } } /// <summary> /// 業務系統配置選項 /// </summary> public class FxOptions { public FxOptions() { } /// <summary> /// 默認資料庫類型 /// </summary> public DatabaseType DefaultDatabaseType { get; set; } = DatabaseType.SqlServer; /// <summary> /// 資料庫連接配置 /// </summary> public IDictionary<string, DbConnectionOptions> DbConnections { get; set; } } public class FxOptionsSetup: IConfigureOptions<FxOptions> { private readonly IConfiguration _configuration; public FxOptionsSetup(IConfiguration configuration) { _configuration = configuration; } /// <summary> /// 配置options各屬性資訊 /// </summary> /// <param name="options"></param> public void Configure(FxOptions options) { SetDbConnectionsOptions(options); // ... } private void SetDbConnectionsOptions(FxOptions options) { var dbConnectionMap = new Dictionary<string, DbConnectionOptions>(); options.DbConnections = dbConnectionMap; IConfiguration section = _configuration.GetSection("FxCore:DbConnections"); Dictionary<string, DbConnectionOptions> dict = section.Get<Dictionary<string, DbConnectionOptions>>(); if (dict == null || dict.Count == 0) { string connectionString = _configuration["ConnectionStrings:DefaultDbContext"]; if (connectionString == null) { return; } dbConnectionMap.Add("DefaultDb", new DbConnectionOptions { ConnectionString = connectionString, DatabaseType = options.DefaultDatabaseType }); return; } var ambiguous = dict.Keys.GroupBy(d => d).FirstOrDefault(d => d.Count() > 1); if (ambiguous != null) { throw new Exception($"數據上下文配置中存在多個配置節點擁有同一個資料庫連接名稱，存在二義性：{ambiguous.First()}"); } foreach (var db in dict) { dbConnectionMap.Add(db.Key, db.Value); } } } /// <summary> /// DbContextOptionsBuilder配置選項 /// </summary> public class DbContextOptionsBuilderOptions { /// <summary> /// 配置DbContextOptionsBuilder, dbName指定資料庫名稱, 為null時表示所有資料庫,默認為null /// </summary> /// <param name="build"></param> /// <param name="dbName"></param> /// <param name="dbContextType"></param> public DbContextOptionsBuilderOptions(DbContextOptionsBuilder build, string dbName = null, Type dbContextType = null) { Builder = build; DbName = dbName; DbContextType = dbContextType; } public DbContextOptionsBuilder Builder { get; } public string DbName { get; } public Type DbContextType { get; } }FxOptions是業務系統的配置選項(隨便取得), 在通過service.GetService<IOptions
public interface IDbContextOptionsBuilderUser { /// <summary> /// 獲取 資料庫類型名稱，如 SQLSERVER，MYSQL，SQLITE等 /// </summary> DatabaseType Type { get; } /// <summary> /// 使用資料庫 /// </summary> /// <param name="builder">創建器</param> /// <param name="connectionString">連接字元串</param> /// <returns></returns> DbContextOptionsBuilder Use(DbContextOptionsBuilder builder, string connectionString); } public class SqlServerDbContextOptionsBuilderUser : IDbContextOptionsBuilderUser { public DatabaseType Type => DatabaseType.SqlServer; public DbContextOptionsBuilder Use(DbContextOptionsBuilder builder, string connectionString) { return builder.UseSqlServer(connectionString); } }IDbContextOptionsBuilderUser介面用來適配不同的資料庫來源
使用
{ "FxCore": { "DbConnections": { "TestDb": { "ConnectionString": "xxx", "DatabaseType": "SqlServer" }, "TestDb_Read": { "ConnectionString": "xxx", "DatabaseType": "SqlServer" } } } } class Program { static void Main(string[] args) { var config = new ConfigurationBuilder() .AddJsonFile("appsettings.json") .Build(); var services = new ServiceCollection() .AddSingleton<IConfiguration>(config) .AddOptions() .AddSingleton<IConfigureOptions<FxOptions>, FxOptionsSetup>() .AddScoped<IDbProvider, DbProvider>() .AddSingleton<IUnitOfWorkFactory, UnitOfWorkFactory>() .AddSingleton<IRepositoryFactory, RepositoryFactory>() .AddSingleton<IDbContextOptionsBuilderUser, SqlServerDbContextOptionsBuilderUser>() .AddSingleton<DbContextOptionsBuilderOptions>(new DbContextOptionsBuilderOptions(new DbContextOptionsBuilder<TestDbContext>(), null, typeof(TestDbContext))); var serviceProvider = services.BuildServiceProvider(); var dbProvider = serviceProvider.GetRequiredService<IDbProvider>(); var uow = dbProvider.GetUnitOfWork<TestDbContext>("TestDb"); // 訪問主庫 var repoDbTest = uow.GetRepository<DbTest, int>(); var obj = new DbTest { Name = "123", Date = DateTime.Now.Date }; repoDbTest.Insert(obj); uow.SaveChanges(); Console.ReadKey(); var uow2 = dbProvider.GetUnitOfWork<TestDbContext>("TestDb_Read"); var uow2 = dbProvider.GetUnitOfWork<TestDbContext>("TestDb_Read"); // 訪問從庫 var repoDbTest2 = uow2.GetReadOnlyRepository<DbTest, int>(); var data2 = repoDbTest2.GetFirstOrDefault(); Console.WriteLine($"id: {data2.Id} name: {data2.Name}"); Console.ReadKey(); } }這裡直接用控制台來做一個例子,中間多了一個Console.ReadKey()是因為我本地沒有配置主從模式,所以實際上我是先插入數據,然後複製到另一個資料庫里,再進行讀取的.
總結
本文給出的解決方案適用於系統中存在多個不同的上下文,能夠適應複雜的業務場景.但對已有程式碼的侵入性比較大,不知道有沒有更好的方案,歡迎一起探討.
