如何在所有C#服务中复用多租户数据库切换代码？

方案1：抽象基类封装逻辑 #

把修改连接字符串的通用逻辑抽成抽象基类，所有需要该逻辑的服务都继承这个基类，彻底避免重复代码。

public abstract class BaseTenantService
{
    protected readonly erp_colombiaContext _context;

    protected BaseTenantService(erp_colombiaContext context, IHttpContextAccessor httpContextAccessor)
    {
        _context = context;
        var user = httpContextAccessor.HttpContext?.User;
        if (user?.Claims.Any() == true)
        {
            var companyName = user.Claims.FirstOrDefault(x => x.Type == "CompanyName")?.Value;
            if (!string.IsNullOrEmpty(companyName))
            {
                var connection = _context.Database.GetDbConnection();
                connection.ConnectionString = connection.ConnectionString.Replace("erp_colombia", companyName);
            }
        }
    }
}

业务服务只需继承基类，专注自身业务逻辑：

public class MyService : BaseTenantService, IMyService
{
    public MyService(erp_colombiaContext context, IHttpContextAccessor httpContextAccessor)
        : base(context, httpContextAccessor)
    {
        // 这里写当前服务的特有逻辑
    }
}

方案2：扩展方法封装逻辑 #

把修改连接字符串的逻辑封装成DbContext的扩展方法，每个服务里直接调用即可，代码更轻量化。

public static class TenantDbContextExtensions
{
    public static void SwitchToTenantDatabase(this erp_colombiaContext context, IHttpContextAccessor httpContextAccessor)
    {
        var user = httpContextAccessor.HttpContext?.User;
        if (user?.Claims.Any() == true)
        {
            var companyName = user.Claims.FirstOrDefault(x => x.Type == "CompanyName")?.Value;
            if (!string.IsNullOrEmpty(companyName))
            {
                var connection = context.Database.GetDbConnection();
                connection.ConnectionString = connection.ConnectionString.Replace("erp_colombia", companyName);
            }
        }
    }
}

业务服务中调用扩展方法：

public class MyService : IMyService
{
    private readonly erp_colombiaContext _context;

    public MyService(erp_colombiaContext context, IHttpContextAccessor httpContextAccessor)
    {
        _context = context;
        _context.SwitchToTenantDatabase(httpContextAccessor);
    }
}

方案3：EF Core拦截器（全局生效，推荐） #

利用EF Core的DbConnectionInterceptor，在数据库连接打开前自动替换数据库名称，无需在每个服务中编写任何代码，全局统一处理。

public class TenantConnectionInterceptor : DbConnectionInterceptor
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public TenantConnectionInterceptor(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public override InterceptionResult ConnectionOpening(DbConnection connection, ConnectionEventData eventData, InterceptionResult result)
    {
        ModifyConnectionString(connection);
        return base.ConnectionOpening(connection, eventData, result);
    }

    public override Task<InterceptionResult> ConnectionOpeningAsync(DbConnection connection, ConnectionEventData eventData, InterceptionResult result, CancellationToken cancellationToken = default)
    {
        ModifyConnectionString(connection);
        return base.ConnectionOpeningAsync(connection, eventData, result, cancellationToken);
    }

    private void ModifyConnectionString(DbConnection connection)
    {
        var user = _httpContextAccessor.HttpContext?.User;
        if (user?.Claims.Any() == true)
        {
            var companyName = user.Claims.FirstOrDefault(x => x.Type == "CompanyName")?.Value;
            if (!string.IsNullOrEmpty(companyName) && connection.ConnectionString.Contains("erp_colombia"))
            {
                connection.ConnectionString = connection.ConnectionString.Replace("erp_colombia", companyName);
            }
        }
    }
}

在Program.cs中注册拦截器：

builder.Services.AddDbContext<erp_colombiaContext>(options =>
{
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection"));
    options.AddInterceptors(sp => sp.GetRequiredService<TenantConnectionInterceptor>());
});

builder.Services.AddScoped<TenantConnectionInterceptor>();
builder.Services.AddHttpContextAccessor();

这种方案一劳永逸，所有使用erp_colombiaContext的地方都会自动切换到租户数据库，无需在服务层做任何额外处理。

内容的提问来源于stack exchange，提问作者J.C