Citus是基于PsotgreSQL的扩展，用于切分PsotgreSQL的数据，非常简单地实现数据“切片（sharp）”。如果不使用Citus，则需要开发者自己实现分布式数据访问层（DDAL），实现路由和结果汇总等逻辑，借助Citus可简化开发，是开发者把精力集中在具体的业务逻辑上。

　　对于多租户程序来说，Citus可以帮助企业对数据进行切片，相比于传统的数据管理方式，Citus更智能，操作更为简单，运维成本更低廉。下面演示Citus的简单使用。

Step 01 安装docker和docker-compose（以Docker方式部署Citus）

curl -sSL https://get.docker.com/ | shsudo usermod -aG docker $USER && exec sg docker newgrp `id -gn`
sudo systemctl start dockersudo curl -sSL https://github.com/docker/compose/releases/download/1.19.0/docker-compose-`uname -s`-`uname -m` -o /usr/local/bin/docker-composesudo chmod +x /usr/local/bin/docker-compose

Step 02 安装并启动Citus　

　　Citus有3个版本Citus Community，Citus Cloud（云端版）， Citus Enterprise（支持HA等高级特性），本文使用Citus Community。

curl -sSLO https://raw.githubusercontent.com/citusdata/docker/master/docker-compose.ymldocker-compose -p citus up -d

Step 03 连接postgres

docker exec -it citus_master psql -U postgres

Step 04 设置数据库用户密码

postgres=# \password postgres          #给postgres用户设置密码
Enter new password:
Enter it again: 

Step 05 创建表

CREATE TABLE tenants (

id uuid NOT NULL,

domain text NOT NULL,

name text NOT NULL,

description text NOT NULL,

created_at timestamptz NOT NULL,

updated_at timestamptz NOT NULL

);

CREATE TABLE questions (

id uuid NOT NULL,

tenant_id uuid NOT NULL,

title text NOT NULL,

votes int NOT NULL,

created_at timestamptz NOT NULL,

updated_at timestamptz NOT NULL

);

ALTER TABLE tenants ADD PRIMARY KEY (id);

ALTER TABLE questions ADD PRIMARY KEY (id, tenant_id);

Step 06 告知Citus如何对数据进行切片

SELECT create_distributed_table('tenants', 'id');
SELECT create_distributed_table('questions', 'tenant_id');

Step 07 初始化数据

INSERT INTO tenants VALUES (

'c620f7ec-6b49-41e0-9913-08cfe81199af',

'bufferoverflow.local',

'Buffer Overflow',

'Ask anything code-related!',

now(),

now());

INSERT INTO tenants VALUES (

'b8a83a82-bb41-4bb3-bfaa-e923faab2ca4',

'dboverflow.local',

'Database Questions',

'Figure out why your connection string is broken.',

now(),

now());

INSERT INTO questions VALUES (

'347b7041-b421-4dc9-9e10-c64b8847fedf',

'c620f7ec-6b49-41e0-9913-08cfe81199af',

'How do you build apps in ASP.NET Core?',

1,

now(),

now());

INSERT INTO questions VALUES (

'a47ffcd2-635a-496e-8c65-c1cab53702a7',

'b8a83a82-bb41-4bb3-bfaa-e923faab2ca4',

'Using postgresql for multitenant data?',

2,

now(),

now());

Step 08 新建ASP.NET Core Web应用程序，并添加引用

• 安装“Npgsql.EntityFrameworkCore.PostgreSQL”包

　　Npgsql.EntityFrameworkCore.PostgreSQL：支持Entity Framework Core操作PostgreSQL。

• 安装“SaasKit.Multitenancy”包

　　SaasKit.Multitenancy：支持ASP.NET Core开发多租户应用。

Step 09 创建models

using System;

namespace QuestionExchange.Models

{

public class Question

{

public Guid Id { get; set; }

public Tenant Tenant { get; set; }

public string Title { get; set; }

public int Votes { get; set; }

public DateTimeOffset CreatedAt { get; set; }

public DateTimeOffset UpdatedAt { get; set; }

}

}

using System;

namespace QuestionExchange.Models

{

public class Tenant

{

public Guid Id { get; set; }

public string Domain { get; set; }

public string Name { get; set; }

public string Description { get; set; }

public DateTimeOffset CreatedAt { get; set; }

public DateTimeOffset UpdatedAt { get; set; }

}

}

using System.Collections.Generic;

namespace QuestionExchange.Models

{

public class QuestionListViewModel

{

　　public IEnumerable<Question> Questions { get; set; }

}

}

Step 10 创建数据上下文

using System.Linq;

using Microsoft.EntityFrameworkCore;

using QuestionExchange.Models;

namespace QuestionExchange

{

public class AppDbContext : DbContext

{

public AppDbContext(DbContextOptions<AppDbContext> options)

: base(options)

{

}

public DbSet<Tenant> Tenants { get; set; }

public DbSet<Question> Questions { get; set; }

/// <summary>

/// C# classes and properties are PascalCase by convention, but your Postgres tables and columns are lowercase (and snake_case).

/// The OnModelCreating method lets you override the default name translation and let Entity Framework Core know how to find

/// the entities in your database.

/// </summary>

/// <param name="modelBuilder"></param>

protected override void OnModelCreating(ModelBuilder modelBuilder)

{

var mapper = new Npgsql.NpgsqlSnakeCaseNameTranslator();

var types = modelBuilder.Model.GetEntityTypes().ToList();

// Refer to tables in snake_case internally

types.ForEach(e => e.Relational().TableName = mapper.TranslateMemberName(e.Relational().TableName));

// Refer to columns in snake_case internally

types.SelectMany(e => e.GetProperties())

.ToList()

.ForEach(p => p.Relational().ColumnName = mapper.TranslateMemberName(p.Relational().ColumnName));

}

}

}

Step 11 为SaaSKit实现解析器

using System;

using System.Collections.Generic;

using System.Threading.Tasks;

using Microsoft.AspNetCore.Http;

using Microsoft.EntityFrameworkCore;

using Microsoft.Extensions.Caching.Memory;

using Microsoft.Extensions.Logging;

using SaasKit.Multitenancy;

using QuestionExchange.Models;

namespace QuestionExchange

{

public class CachingTenantResolver : MemoryCacheTenantResolver<Tenant>

{

private readonly AppDbContext _context;

public CachingTenantResolver(

AppDbContext context, IMemoryCache cache, ILoggerFactory loggerFactory)

: base(cache, loggerFactory)

{

_context = context;

}

// Resolver runs on cache misses

protected override async Task<TenantContext<Tenant>> ResolveAsync(HttpContext context)

{

var subdomain = context.Request.Host.Host.ToLower();

var tenant = await _context.Tenants

.FirstOrDefaultAsync(t => t.Domain == subdomain);

if (tenant == null) return null;

return new TenantContext<Tenant>(tenant);

}

protected override MemoryCacheEntryOptions CreateCacheEntryOptions()

=> new MemoryCacheEntryOptions().SetAbsoluteExpiration(TimeSpan.FromHours(2));

protected override string GetContextIdentifier(HttpContext context)

=> context.Request.Host.Host.ToLower();

protected override IEnumerable<string> GetTenantIdentifiers(TenantContext<Tenant> context)

=> new string[] { context.Tenant.Domain };

}

}

Step 12 修改Startup.cs

using Microsoft.AspNetCore.Builder;

using Microsoft.AspNetCore.Hosting;

using Microsoft.EntityFrameworkCore;

using Microsoft.Extensions.Configuration;

using Microsoft.Extensions.DependencyInjection;

using QuestionExchange.Models;

namespace QuestionExchange

{

public class Startup

{

public Startup(IConfiguration configuration)

{

Configuration = configuration;

}

public IConfiguration Configuration { get; }

// This method gets called by the runtime. Use this method to add services to the container.

public void ConfigureServices(IServiceCollection services)

{

var connectionString = "Server=192.168.99.102;Port=5432;Database=postgres;Userid=postgres;Password=yourpassword;";

services.AddEntityFrameworkNpgsql()

.AddDbContext<AppDbContext>(options => options.UseNpgsql(connectionString));

services.AddMultitenancy<Tenant, CachingTenantResolver>();

services.AddMvc();

}

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.

public void Configure(IApplicationBuilder app, IHostingEnvironment env)

{

if (env.IsDevelopment())

{

app.UseDeveloperExceptionPage();

app.UseBrowserLink();

}

else

{

app.UseExceptionHandler("/Home/Error");

}

app.UseStaticFiles();

app.UseMultitenancy<Tenant>();

app.UseMvc(routes =>

{

routes.MapRoute(

name: "default",

template: "{controller=Home}/{action=Index}/{id?}");

});

}

}

}

Step 13 创建View和Controller

@inject Tenant Tenant

@model QuestionListViewModel

@{

ViewData["Title"] = "Home Page";

}

<div class="row">

<div class="col-md-12">

<h1>Welcome to <strong>@Tenant.Name</strong></h1>

<h3>@Tenant.Description</h3>

</div>

</div>

<div class="row">

<div class="col-md-12">

<h4>Popular questions</h4>

<ul>

@foreach (var question in Model.Questions)

{

<li>@question.Title</li>

}

</ul>

</div>

</div>

using Microsoft.AspNetCore.Mvc;

using Microsoft.EntityFrameworkCore;

using QuestionExchange.Models;

using System.Diagnostics;

using System.Linq;

using System.Threading.Tasks;

namespace QuestionExchange.Controllers

{

public class HomeController : Controller

{

private readonly AppDbContext _context;

private readonly Tenant _currentTenant;

public HomeController(AppDbContext context, Tenant tenant)

{

_context = context;

_currentTenant = tenant;

}

public async Task<IActionResult> Index()

{

var topQuestions = await _context

.Questions

.Where(q => q.Tenant.Id == _currentTenant.Id)

.OrderByDescending(q => q.UpdatedAt)

.Take(5)

.ToArrayAsync();

var viewModel = new QuestionListViewModel

{

Questions = topQuestions

};

return View(viewModel);

}

public IActionResult About()

{

ViewData["Message"] = "Your application description page.";

return View();

}

public IActionResult Contact()

{

ViewData["Message"] = "Your contact page.";

return View();

}

public IActionResult Error()

{

return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });

}

}

}

Step 14 运行站点

　　首先需要修改本地Hosts文件，添加：

127.0.0.1 bufferoverflow.local127.0.0.1 dboverflow.local

　　运行cmd（命令行），输入以下命令，刷新DNS：

ipconfig /flushdns

　　分别使用不同Url浏览站点，可以看到之前插入的测试数据在不同租户下显示不同：

　　以上，简单演示了如何基于Citus开发多租户应用。此外，Citus还比较适合开发需要快速返回查询结果的应用（比如“仪表板”等）。

　　本文演示的例子比较简单，仅仅是演示了使用Citus开发多租户应用的可能。具体实践中，还涉及到具体业务以及数据库切片技巧等。建议阅读微软的《Cloud Design Patterns Book》中的Sharding模式部分，以及Citus的官方技术文档。

参考资料：

　　https://github.com/citusdata/citus

　　https://www.citusdata.com/blog/2018/01/22/multi-tenant-web-apps-with-dot-net-core-and-postgres

　　https://docs.citusdata.com/en/v7.1/aboutcitus/what_is_citus.html

原文地址:https://www.cnblogs.com/MeteorSeed/p/8446154.html

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