EF Core 实现读写分离的最佳方案
前言
公司以前使用Ado.net和Dapper进行数据访问层的操做, 进行读写分离也比较简单, 只要使用对应的数据库链接字符串便可. 而最近要迁移到新系统中,新系统使用.net core和EF Core进行数据访问. 因此趁着国庆假期拿出一两天时间研究了一下如何EF Core进行读写分离.html
思路
根据园子里的Jeffcky大神的博客, 参考
EntityFramework Core进行读写分离最佳实践方式，了解一下（一）？
EntityFramework Core进行读写分离最佳实践方式，了解一下（二）？sql
最简单的思路就是使用手动切换EF Core上下文的链接, 即context.Database.GetDbConnection().ConnectionString = "xxx", 但必需要先建立上下文, 再关闭以前的链接, 才能进行切换
另外一种方式是经过监听Diagnostic来将进行查询的sql切换到从库执行, 这种方式虽然能够实现无感知的切换操做, 但不能知足公司的业务需求. 在后台管理或其余对数据实时性要求比较高的项目里,查询操做也都应该走主库,而这种方式却会切换到从库去. 另外一方面就是倘若公司的库比较多,每种业务都对应了一个库, 每一个库都对应了一种DbContext, 这种状况下, 要实现自动切换就变得很复杂了.数据库
上面的两种方式都是从切换数据库链接入手,可是频繁的切换数据库链接势必会对性能形成影响. 我认为最理想的方式是要避免数据库链接的切换, 且可以适应多DbContext的状况, 在建立上下文实例时,就指定好是访问主库仍是从库, 而不是在后期再进行数据库切换. 所以, 在上下文实例化时,就传入相应的数据库链接字符串, 这样一来DbContext的建立就须要交由咱们本身来进行, 就不是由DI容器进行建立了. 同时仓储应该区分为只读和可读可写两种,以防止其余人对从库进行写操做.express
实现
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接口是只读仓储接口,提供查询相关方法,IRepository接口是可读可写仓储接口,提供增删查改等方法, 接口的实现就那些东西这里就省略了.json
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提供仓储对象的实例化c#
public interface IUnitOfWork : IDisposable
{
public DbContext DbContext { get; }
/// <summary>
/// 获取只读仓储对象
/// </summary>
IReadOnlyRepository<TEntity, TKey> GetReadOnlyRepository<TEntity, TKey>()
where TEntity : class, IEntity<TKey>
where TKey : IEquatable<TKey>;
/// <summary>
/// 获取仓储对象
/// </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;
}
// 其余略
}
/// <summary>
/// 数据库提供者接口
/// </summary>
public interface IDbProvider : IDisposable
{
/// <summary>
/// 根据上下文类型及数据库名称获取UnitOfWork对象, dbName为null时默认为第一个数据库名称
/// </summary>
IUnitOfWork GetUnitOfWork(Type dbContextType, string dbName = null);
}
IDbProvider 接口, 根据上下文类型和配置文件中的数据库链接字符串名称建立IUnitOfWork, 在DI中的生命周期是Scoped,在销毁的同时会销毁数据库上下文对象, 下面是它的实现, 为了提升性能使用了Expression来代替反射.app
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("没法获取数据库配置");
}
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("没法获取匹配的DbContextOptionsBuilder");
}
var dbUser = _serviceProvider.GetServices<IDbContextOptionsBuilderUser>()?.FirstOrDefault(u => u.Type == dbConnectionOptions.DatabaseType);
if (dbUser == null)
{
throw new Exception($"没法解析类型为“{dbConnectionOptions.DatabaseType}”的 {typeof(IDbContextOptionsBuilderUser).FullName} 实例");
}
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建立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("没法获取有效的上下文构造器");
}
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>
/// 业务系统配置选项
/// </summary>
public class FxOptions
{
public FxOptions()
{
}
/// <summary>
/// 默认数据库类型
/// </summary>
public DatabaseType DefaultDatabaseType { get; set; } = DatabaseType.SqlServer;
/// <summary>
/// 数据库链接配置
/// </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各属性信息
/// </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($"数据上下文配置中存在多个配置节点拥有同一个数据库链接名称，存在二义性：{ambiguous.First()}");
}
foreach (var db in dict)
{
dbConnectionMap.Add(db.Key, db.Value);
}
}
}
/// <summary>
/// DbContextOptionsBuilder配置选项
/// </summary>
public class DbContextOptionsBuilderOptions
{
/// <summary>
/// 配置DbContextOptionsBuilder, dbName指定数据库名称, 为null时表示全部数据库,默认为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是业务系统的配置选项(随便取得), 在经过service.GetService<IOptions
public interface IDbContextOptionsBuilderUser
{
/// <summary>
/// 获取 数据库类型名称，如 SQLSERVER，MYSQL，SQLITE等
/// </summary>
DatabaseType Type { get; }
/// <summary>
/// 使用数据库
/// </summary>
/// <param name="builder">建立器</param>
/// <param name="connectionString">链接字符串</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接口用来适配不一样的数据库来源性能
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"); // 访问主库
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"); // 访问从库
var repoDbTest2 = uow2.GetReadOnlyRepository<DbTest, int>();
var data2 = repoDbTest2.GetFirstOrDefault();
Console.WriteLine($"id: {data2.Id} name: {data2.Name}");
Console.ReadKey();
}
}
这里直接用控制台来作一个例子,中间多了一个Console.ReadKey()是由于我本地没有配置主从模式,因此实际上我是先插入数据,而后复制到另外一个数据库里,再进行读取的.ui
总结
本文给出的解决方案适用于系统中存在多个不一样的上下文,可以适应复杂的业务场景.但对已有代码的侵入性比较大,不知道有没有更好的方案,欢迎一块儿探讨.
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