What’s The Relation Between Rack, Rack Application, Rack Middleware, Rackup & Rails Application?

A mouth full of terms indeed! How else could I have shorten the title? Anyways, since you’re reading this, I’m sure you are confused as I am when I first came into these terms myself. Hope this post helps you understand better what all these are and how they relate to one another.

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What is Rack?

Traditionally, ruby web framework developers would write an adapter for each web server they wanted their web framework to support. This is obviously unsustainable, hence a standard solutions is needed. Rack to the Rescue! Rack defines a standard way of interaction between web servers and ruby web applications. Rack basically is both a simple specification (the standard) and ruby library for connecting web servers to ruby web applications. 

The Specification: Defines two things: an environment (env), which is a hash that contains CGI-like headers describing the request and a response, which is an array of values including the [response code, response headers, and response body].

Ruby Library: List of all modules and classes are available at http://rack.rubyforge.org/doc/classes/Rack.html

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Rails 3 + Arel: Left outer join with table aliasing (Part 2)

It wasn’t until I read an article by Ernie Miller on MetaWhere, that I found out the lies that “.to_sql” has been putting me up with. Apparently, “.to_sql” doesn’t show you everything under the hood. For example:

Task.includes(:creator).where(“users.username LIKE ‘%manager%’”).to_sql
# Outputs “SELECT `tasks`.* FROM `tasks` WHERE (users.username LIKE ‘%manager%’)”

With MetaWhere’s own “.debug_sql”, I was then able to see the complete SQL query that was being executed against my tables.

Task.includes(:creator).where(“users.username LIKE ‘%manager%’”).debug_sql
# Outputs “SELECT * FROM tasks LEFT OUTER JOIN users ON users.id = tasks.creator_id AND users.deleted_at IS NULL WHERE (users.username LIKE ‘%manager%’)”

Now that the issue with “Includes” has been straightened, lets see the updated Task example that I’ve given in Part I.

IMPORTANT: Take note of the updated alias name for the Users table. I’ve updated it to “creators_tasks” as including :creators into your query will result in a default aliasing of users table as “creators_users” in SQL