關(guān)于數(shù)據(jù)庫(kù), 關(guān)于 MVC, 也關(guān)于 React的兩篇文章讀后感

2015-08-17 09:59:49

今天看了兩篇文章, 我覺(jué)得對(duì)我的影響會(huì)很大, 當(dāng)然, 都是 React 相關(guān)的:一篇是 Martin Kleppmann 在 Strangeloop 2014 大會(huì)上的演講, 有視頻, 也有文字版, 關(guān)于數(shù)據(jù)庫(kù):另一篇是 Christian Alfoni 關(guān)于 Flux 的文章, 從 Twitter 上看到的, 關(guān)于 MVC 架構(gòu):

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兩篇文章

今天看了兩篇文章, 我覺(jué)得對(duì)我的影響會(huì)很大, 當(dāng)然, 都是 React 相關(guān)的:

一篇是 Martin Kleppmann 在 Strangeloop 2014 大會(huì)上的演講, 有視頻, 也有文字版, 關(guān)于數(shù)據(jù)庫(kù):

Turning the database inside-out with Apache Samza

http://www.confluent.io/blog/turning-the-database-inside-out-with-apac...

另一篇是 Christian Alfoni 關(guān)于 Flux 的文章, 從 Twitter 上看到的, 關(guān)于 MVC 架構(gòu):

Why we are doing MVC and FLUX wrong

http://www.christianalfoni.com/articles/2015_08_02_Why-we-are-doing-MV...

https://www.youtube.com/watch?v=xCIv4-Q2dtA

http://www.christianalfoni.com/todomvc/#/

來(lái)源

前面一篇是在 Redux 的文檔上看到的, 這文檔上有不少我關(guān)心的技術(shù):

http://gaearon.github.io/redux/index.html

The Elm Architecture a great intro to modeling state updates with reducers;
Turning the database inside-out for blowing my mind;
Developing ClojureScript with Figwheel for convincing me that re-evaluation should "just work"
Webpack for Hot Module Replacement;
Flummox for teaching me to approach Flux without boilerplate or singletons;
disto for a proof of concept of hot reloadable Stores;
NuclearJS for proving this architecture can be performant;
Om for popularizing the idea of a single state atom;
Cycle for showing how often a function is the best tool;
React for the pragmatic innovation.

Redux 的作者最近在 Twitter 上非常活躍, 總是在發(fā)各種 Redux 相關(guān)的消息

我的感覺(jué)是 Redux 一出來(lái), React 社區(qū)跟函數(shù)式編程, 跟未來(lái), 的距離又拉進(jìn)了一步, 一大步

包括 Clojure, Elm, PureScript 在 Twitter 上也非常地活躍... 當(dāng)然也因?yàn)槲谊P(guān)注多了這些人

然后我就常常在想, 函數(shù)式編程是真的在復(fù)興了對(duì)吧, 到處都出現(xiàn)了?

關(guān)于數(shù)據(jù)庫(kù)

***篇文章很難懂, 還好圖片多, 大致的意思就是重新思考一下數(shù)據(jù)庫(kù)

常用的數(shù)據(jù)庫(kù)都在基于上世紀(jì)的硬件條件設(shè)計(jì)的, 受到各種限制

如果我們重新思考一下數(shù)據(jù)庫(kù)的應(yīng)用, 應(yīng)該怎么考慮設(shè)計(jì)新的方案?

然后作者梳理了一下數(shù)據(jù)庫(kù)應(yīng)用當(dāng)中的幾個(gè)重要的點(diǎn):

Replication 數(shù)據(jù)庫(kù)同步

Secondary indexing 輔助索引

Cache 緩存

Materialized views 物化視圖

We first discussed replication, i.e. keeping a copy of the same data on multiple machines. It generally works very well, so we’ll give it a green smiley. There are some operational quirks with some databases, and some of the tooling is a bit weird, but on the whole it’s mature, well-understood, and well-supported.
Similarly, secondary indexing works very well. You can build a secondary index concurrently with processing write queries, and the database somehow manages to do this in a transactionally consistent way.
On the other hand, application-level caching is a complete mess. Red frowny face.
And materialized views are so-so: the idea is good, but the way they’re implemented is not what you’d want from a modern application development platform. Maintaining the materialized view puts additional load on the database, while actually the whole point of a cache is to reduce load on the database!

實(shí)際開(kāi)發(fā)的感受而言, 前兩者在數(shù)據(jù)庫(kù)內(nèi)部實(shí)現(xiàn)很高效, 也不需要太多操心

Cache 相對(duì)來(lái)說(shuō)就是一團(tuán)亂麻的實(shí)現(xiàn), 非常難管理

Materialized views 還不錯(cuò), 可是不適合編程, 靈活度低, 不能做太多事情

那么作者想, 如果反過(guò)來(lái), 把數(shù)據(jù)庫(kù)同步機(jī)制作為數(shù)據(jù)庫(kù)設(shè)計(jì)的核心, 能夠改善?

數(shù)據(jù)庫(kù)內(nèi)部通過(guò) Logical log 的形式, 將所有的數(shù)據(jù)保存下來(lái), 作為同步的手法

這里說(shuō)的是 Apache Kafka, 我似乎記得 MongoDB, Redux, Docker, Nix 都有類(lèi)似的做法

這里的 Log 有點(diǎn)像 Flux 當(dāng)中的 Action, 隨著時(shí)間就形成了 Stream, 用于同步數(shù)據(jù)

作者后來(lái)更加延伸一步, 覺(jué)得從數(shù)據(jù)庫(kù)到屏幕像素, 整個(gè)都是數(shù)據(jù)同步的一個(gè)過(guò)程

比如說(shuō)數(shù)據(jù)庫(kù)的一些查詢(xún)結(jié)果, 相當(dāng)于 Tables 的 Materialized views, 這樣一層抽象

那么, 緩存, HTML DOM, 界面像素, 其實(shí)就是后面緊跟的一層層抽象

編寫(xiě)應(yīng)用而言, 如果整個(gè)是 Reactive 的, 后面跟著前面自動(dòng)更新, 那將是非常高效的

考慮一下, HTML 是后端渲染的, 如果數(shù)據(jù)庫(kù)更新了, HTML 自動(dòng)局部更新多好

這樣就需要引入 Stream 的機(jī)制了. 只不過(guò), 前端的實(shí)現(xiàn)通常是發(fā)布/訂閱模式

現(xiàn)在的 Meteor 是個(gè)特別知名的例子. Meteor 用 MongoDB 的同步機(jī)制的話可能還更像

這篇文章指出類(lèi)似的方案已經(jīng)有很多人在貢獻(xiàn), 在開(kāi)發(fā)新的工具來(lái)實(shí)現(xiàn)了

而特別讓我在意的是, 整套思路至少在驗(yàn)證我用 Cumulo 探索的方案至少出發(fā)點(diǎn)很不錯(cuò)

實(shí)際上 Datomic, Redux 這些我在關(guān)注的技術(shù), 也是朝著類(lèi)似的方向前進(jìn)的

有不小的可能, 未來(lái)我們開(kāi)發(fā)應(yīng)用的方式, 整體是就是依照這套辦法做下去

關(guān)于 MVC

另一篇文章是在講 MVC 和 Flux 的問(wèn)題, ***拋出自己基于 React 寫(xiě)的 Cerebral

從文章的章節(jié)標(biāo)題可以看到具體的脈絡(luò),

MVC 在前端遇到什么問(wèn)題, Flux 怎么改進(jìn), 還能怎么改進(jìn):

Traditional MVC
Application state
State in traditional MVC
When we moved to the frontend
The router is not a controller
The view layer bypassed the controller layer
No concept of a single state store
State in the view layer
What FLUX improved
Fixing the problem
A single state store
A controller with middleware
The views talk to the controller
Just do the routing
So what benefits do I really get?
Summary

后端而言, 各個(gè) Part 之間隔離非常明顯, MVC 都有各自的程序和語(yǔ)言來(lái)抽象

在前端, 所有東西突然聚在了一起, 催生出特別多原來(lái)沒(méi)有的做法, 也面臨各種問(wèn)題

Multiple views
State also inside views
Multiple models
We bypass the view controller model flow
The router is no longer the only entry point for state change

Flux 對(duì)問(wèn)題做了一些糾正, 避免了狀態(tài)分散在 View 當(dāng)中的狀況, 跟 MVC 更加貼近

然而其中一些 Part 的用法, 依然存在著問(wèn)題:

The FLUX architecture uses multiple models (stores). With traditional MVC you only have one model, your database. Multiple stores quickly causes problems when a dispatch needs to reach more than one store and especially if one store needs to know about state in an other
There is no concept of middleware like in a traditional controller. This quickly introduced the concept of action creators. They are much like a single middleware that is responsible for doing everything needed related to a request from the view layer, often doing multiple dispatches to the stores
When the view layer wants to get some state they still do it directly from the model layer, making unnecessary complex dependencies in the views

作者也提出了具體的解決方案, 最主要的是數(shù)據(jù)和狀態(tài)要統(tǒng)一到 Model 當(dāng)中: