database design problem.

[willy Hakizimana]

First of all, this community is amazing at how fast questions are answered. I have learned so much.


I am designing an app with models that look like this.

Country(country_id(PK), country_name, gdp, gdp_growth, income_per_capita)

Product(product_id(PK), product_name, country_id(FK), imports_volume)

Since I have to show imports_volume for the same product in each country, I am stumped on how to design the db.


 

[Larry Martell]

I'd have a country table, a product table, and a product_country table:

Country(country_id(PK), country_name, gdp, gdp_growth, income_per_capita)

Product(product_id(PK), product_name)
Product_Country(id(PK), product_id(FK), country_id(FK), imports_volume)

[Alvin Lindstam]

Actually, the Django term for this is "through". Not via.

See https://docs.djangoproject.com/en/1.6/topics/db/models/#extra-fields-on-many-to-many-relationships on how to specify the intermediate table to be used in many-to-many relationships.


Den lördagen den 15:e mars 2014 kl. 18:01:02 UTC+1 skrev Dennis Lee Bieber:

On Sat, 15 Mar 2014 08:38:03 -0700 (PDT), willy Hakizimana
<will...@gmail.com> declaimed the following:

        If I understand your statement, you need (paraphrased) the
imports_volume to be for each product for each country...

        That means it does NOT belong in either Country or Product tables.

Country(*countryID*, Name, gdp, gdp_growth, per_capita_income)

Product(*productID*,  Name)

Imports(_countryID_, _productID_, import_volume)

        In Django terms (I believe), this is a many2many relationship using a
via table (the native m2m would create a table with _countryID_,
_productID_ foreign keys only; the via table lets you add data specific to
the relationship itself... An intersect table in older database
terminology)

>
>
--
        Wulfraed                 Dennis Lee Bieber         AF6VN
    wlf...@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

[willy Hakizimana]

Thank you guys so much. You guys rock!

[Lachlan Musicman]

I would make the imports model an "intermediate model" - see here:

https://docs.djangoproject.com/en/1.6/topics/db/models/#extra-fields-on-many-to-many-relationships

L.

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