On 13 July 2010 06:03, Adrian Zatta <[email protected]> wrote:
> Hi everyone,
> I have the following basic rules:
> Subject has many elements
> Element has many subjects
> Element has many knowledges which are either enabled or required
> Element has many skills which are either enabled or required
>
> I have designed the schema to have 6 tables, Subjects, Elements,
> PriorKnowledge, PriorSkills, EnabledKnowledge and EnabledSkills.
You talked about required earlier, is that the same as prior?
Is there a good reason why you don't just put PriorKnowledge and
EnabledKnowledge in the same class and table with a boolean to
indicate which?
>
> Now to my problem. I am trying to build a page that will display all
> this information. It will display a subject and all its elements, and
> all of the elements prior and enabled, knowledges and skills.
>
> The thought that I had was to use has_many :through relationships, but I
> don't know how to handle both prior and enabled cases.
I am obviously missing something, why can't you just say
@element.prior_knowledge
and
@element.enabled_logic
>
> My next thought was to use a sql query to select the knowledge and skill
> elements required and save them as class variables in elements. However
> I don't know how to get the ID of the element i am working with.
>
> This is the SQL query that does the job:
> select description from knowledges where id in (select
> knowledges_id from prior_knowledges where elements_id = 1);
Now you seem to have a 'knowledges' table which you have not mentioned before.
Colin
>
> I had this line in the element.rb file:
> @@pk = Knowlegde.find_by_sql("select description from knowledges
> where id in (select knowledges_id from prior_knowledges where
> elements_id = " + id.to_s + ");")
> But i kept getting a empty array but executing the same command in SQL
> works, and executing the command manually in the console also works.
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