Re: Is the logic in my model correct? Best-case?

That's exactly what I needed.  Thank you *very* much! 

On Mon, Sep 3, 2012 at 8:44 PM, Dennis Lee Bieber <wlfraed@ix.netcom.com> wrote:

On Mon, 3 Sep 2012 18:51:45 -0700 (PDT), Barry Morrison
<bdmorrison@gmail.com> declaimed the following in
gmane.comp.python.django.user:

> Model: http://dpaste.org/dqwmc/
>
> There can be many products.

        Okay, a table of products...

> There can be many distributors.

        and a table of distributors

> A product could have none or more distributors.

        Normal intersect table behavior

> A distributor could only distribute a single product once.

        This clause is unclear...

> A distributor could distribute all products.
>

        This clause is irrelevant -- it doesn't restrict the data (vs if you
had some requirement that a distributor carrying products a..m is not
allowed to carry product n)

> I imagine a form (admin side):
>
> Product Name:
> Product Description:
> Product Image:
>
> Distributor 1: Radio Field/Boolean
> Distributor 2: Radio Field/Boolean
> Etc. etc.
>
> For some reason I can't wrap my head around this.

        Your model (per the linked web page) current ties a product instance
to ONE DISTRIBUTOR ONLY.

        In pseudo-SQL, you have defined

create table Distributor
(
        ID      integer autoincrement primary key,      #django adds this
        Name    varchar(255) not null,  #it is redundant to preface fields
                                                                        #with "distributor" when they are
                                                                        #IN the table Distributor
        URL     varchar(255) null,              #URL type is django operation
        Product boolean                 #this field is meaningless as
                                                                        #there is no product referenced
                                                                        #here
);

create table Product
(
        ID      integer autoincrement primary key,
        Name    varchar(255) not null,
        Description     blob,   #or some such large text field
        Image   varchar(255) null,      #image type is django usage
        Distributor     integer foreign key references Distributor (ID),
                        #this basically says that this product can have
                        #only ONE distributor
);

        What you really need is not a one-to-many link (one distributor can
have many products, but each product can only have one distributor) but
a many-to-many linkage.

create table Distributor
(
        ID      integer autoincrement primary key,      #django adds this
        Name    varchar(255) not null,
        URL     varchar(255) null,
);

create table Product
(
        ID      integer autoincrement primary key,
        Name    varchar(255) not null,
        Description     blob,   #or some such large text field
        Image   varchar(255) null,      #image type is django usage
);

create table ProductDistribution
(
        ID      integer autoincrement primary key,
        ProductID       integer foreign key references Product(ID),
        DistributorID   integer foreign key references Distributor(I),
        unique (ProductID, DistributorID)
);

        As I understand it, Django will create the equivalent of
ProductDistribution when you declare a many-to-many relationship in one
of the parent tables.

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

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