Nate Morse

This is easy if you can count in binary. If counting in Base 2 is not a drummed in skill then look here first and maybe here…

Using an integer field (column) in a table, you can store independent boolean flags (variables), all in this one field.

First you can define some bit masks (note the pythony ## inline-comments),
each one only sets one bit ON:

FEATURE_A_BIT   =  1 ## or in base(2) this would look like 00000001
FEATURE_B_BIT   =  2 ## or in base(2) this would look like 00000010
FEATURE_C_BIT   =  4 ## or in base(2) this would look like 00000100
FEATURE_D_BIT   =  8 ## or in base(2) this would look like 00001000

As an example Imagine that our field (let’s call it “features”) is initially set to Zero.  This initial state represents all fearture (A – D) are OFF.

The bit wise OR “|” operator  Adds in the feature_B bit and leaves all other bits just the same.
So for example: To set the feature_B bit ON:  mysql> UPDATE your_table SET features = (features | FEATURE_B_BIT) where id = someid;

    0000000
 |  0000010
 ----------
    0000010  # great the Feature B bit is set ON

The bit wise AND “&” and the NOT “~” operator  Subtracts the feature_B bit, again leaving all other bits just the same.

For example: To set the feature_B bit OFF:  mysql> UPDATE your_table SET features = (features &~ FEATURE_B_BIT) where id = someid;

    0000010  ## the inital value of features
  & 1111101  ## this is just NOT (0000010) from ~ FEATURE_B_BIT
  ---------
    0000000  ## and this is what you wanted: the Feature B bit is reset OFF.

And to retreive a single bit value, with a SELECT statement: mysql> SELECT (features & FEATURE_B_BIT) as feature_B FROM your_table where id = someid;

You can make it more complicated by combining bits and logic, but these are the basics of using “Bit Wise Flags in MySQL.”

In practice you would use this to store data like “opt-in”, “is-valid-format”, or “ok-by-mom” etc… So, really you would replace FEATURE_A_BIT with OPT_IN and FEATURE_B_BIT would be called OK_BY_MOM, but make sure that your bit masks only set one bit, or it gets confusing fast. If you do need to set (or reset) two or more feature bits at once you can OR them together  , like this (OPT_IN | OK_BY_MOM), when you feed that into the bit operations above, you will be setting or resetting all in one go.

By the time anyone develops an application using nodejs and all the related libs, the community may have done some of it for you, and better.

My experience was in a project combining “nodejs”, “express”, and “socket.io” together using the “pubsub” pattern to give a consistent coding API across the client and server code.  No regrets in building it this way, but the coding community is developing new libs so fast, that they may have done it for you before you can finish you code.  It is in the Air, everyone who is using these new Web technologies is moving in the same direction, so it’s really important to keep one ear to the rail (the other ear listening for trains :) while coding…

It only took one week of heads-down development in my own project, for a (possibly) better package to emerge that will do 90% of my coding for me.

So, I am in a rewrite of my app to include this better lib (NowJS.com).

But now, I am not really sure if I am hoping for yet another (even better) package to emerge before get this rewrite out…

Start making websites that use asynchronous sockets.
Stop using request based web programming.
Start listening on channels.
Stop working around the issues in AJAX.
Start emitting messages.
Stop making websites with PHP, C#, Python, Ruby, PERL.
Start coding websites with node.js in Javascript (or Coffeescript).
Stop using a huge server stack.
Start using socket.io (or another similar Web Sockets utility).
Stop creating OO and procedural code.
Start thinking in terms of Events.
Stop the waterfall that is relational data design.
Start working with schema-less data stores.

Enough, It is time to start coding Web 3.0, and to start this, use nodejs, socketio, NoSql, and see why these technologies warrant a version change.