how does ez_where catch =~ and co

rubyonrails-talk
1

Hi all,

I’ve been looking through the ez_where plugin and I’m slowly starting to follow it. One thing that I can’t quite grok is how the =~ , == , === etc methods are caught in the block.

eg in the readme

condition :my_other_table do
    id === [1, 3, 8]
    foo == 'other bar'
    fiz =~ '%faz%'
  end

I can see how the id, foo and fiz methods are caught by using method_missing, but I can’t find out how the =~ and it’s argument is then subsequently caught to be processed.

Can anyone point out how this is done please.

Thanx

2

Hey Daniel-

  Its actually a dual method_missing dispatch. the id and foo are caught in Condition by method missing and then they create a new Clause object for each statement. In the Clause object, method missing catches the == =~ and other operators. Thats the simplified explanation anyway. Its quite a complex interaction that has taken us a while to build up and make work.

  Make sure you check out the new version released yesterday!

http://brainspl.at/articles/2006/10/03/nested-joins-and-ez-where-update

-Ezra

3

Hi Ezra,

Thanx for the response. The code is pretty tricky for me to grok.

Hopefully you don’t mind but I’m looking for some inspiration to create a plugin to generate nested conditions for javascript.

Basically I’m thinking of a plugin that has similar syntax to ez_where that generates conditions based on DOM elements that I can use in an if statement to control behaviors and functions on the client side in javascript.

Then I could generate complex conditional statement that conditionally controlled the visiblity of elements etc.

Does this sound like something that might be useful? When I was looking through ez_where I was thinking that the logic for the nested conditions is essentially the same, with only the output needing to change. I’m not sure if that’s true when thinking of dom elements but it’s a place to start.

Thanx to you and Fabien for writing such a great plugin.

Cheers

4

Hi~

-Ezra

Hi Ezra,

Thanx for the response. The code is pretty tricky for me to grok.

Hopefully you don't mind but I'm looking for some inspiration to create a plugin to generate nested conditions for javascript.

Basically I'm thinking of a plugin that has similar syntax to ez_where that generates conditions based on DOM elements that I can use in an if statement to control behaviors and functions on the client side in javascript.

Then I could generate complex conditional statement that conditionally controlled the visiblity of elements etc.

Does this sound like something that might be useful? When I was looking through ez_where I was thinking that the logic for the nested conditions is essentially the same, with only the output needing to change. I'm not sure if that's true when thinking of dom elements but it's a place to start.

Thanx to you and Fabien for writing such a great plugin.

Cheers

Hey Daniel-

  I am not entirely sure what you want to do here. Are you trying to program this in javascript? Or do you mean a ruby/rails coded plugin that will generate javascript for you? Can you provide me with some examples of what you are trying to generate and what you would want your ruby syntax for this to look like? I might be able to point you in the right direction.

Cheers- -Ezra

5

I’m not exacly sure myself yet of the grand scheme.

At the moment, the overall outcome I want to achive is to be able to conditionally control visibilty of DOM objects in response to activity in the DOM, especially forms.

Something like

form.condition( ‘element5’, :hide ) do

or do

field2 == "go"

and do

  thing.hidden?

  field1 =~ /bla/

end

end

end

to construct

if ( field2.value = “go” || (thing.style.display = “none” && field1.value.match( ‘bla’ ) ) ) { hide_if_shown( element5 ); }

I’m not sure I’m happy with the sytax yet. It looks a bit nasty.

This should be added to an array of conditions that observes form fields and gets fired when something happens.

I’d really like to do this in ruby and not need to resort to raw js unless nessesary, I’ve been checking out UJS today and that looks like it’s pretty nice.

I figured that to do this, first I need to generate the condition inside the if statement. Hence my sudden interest in how to construct nested queries.

I’m hoping that this will lead me to highly interactive and intelligent forms for the occasions where a large form is required for everything, but not everything needs to be filled out, or even wizard style forms on one page.

Do you have any thoughts on whether this is a reasonable idea or not? Any potholes that would be likely if using such a plugin?