Weird associations, how would you do that ?

[Jeremy1 (Jérémy)]

Hi there,

I have some complex situation to solve, and can't manage to find a way which satisfy me ...

Here's the problem :

You have to handle many Users (id, name, email, password). You have a list of many Products (id, name) which are the same for all users. You have some Locations (id, user_id, name) of where to put one product, each user defining his own locations.

BUT

Every user should be able to put his very own "physical instance" of one product in a location OR NOT, which one will, consequently, be different for every user. Moreover, he may specify an alternative name for the product.

So you have to make some model/table that can link product, location, and user altogether. Let's call it MyProducts.

IMO there is 2 ways to go, based on the above : - either you put only the products that have a location in MyProducts - or you duplicate (badbadbad!) all the products from Products in MyProducts, and so for each user, which force you to maintain the same list in both tables, but users and products won't change too often, and it will require less work when you have to know which product has been "modified" or not.

My way of solving this for the moment is the first one :

You have one Product model, that has_many user_products You have one User model, that has_many user_products You have one Location model, that has_many user_products You have one MyProduct model, that belongs_to Product, belongs_to Location, and belongs_to User

This doesn't seem too bad, does it ?

The problem is, in your index view, when you want to list all Products, you have to get an array of all products, and an array of all my_products, and then subtract the products that exist in user_product from the products array, so you get only the product not "modified" by the user, you can display them, and you can then display those in user_product. But they're not ordered. So maybe there is some more work to do so ...

And this looks ugly IMO.

So that's why I'm asking you, how would you do something like that ? Is it a good idea to do as I did ? This looks like a three way association, and I've been taught to never do that but when you can't do anything else.

And above all, is there some Rails-way to do this ? Like using has_and_belongs_to_many in some cases.

PS : I hope my English isn't too bad, I did my best

[Colin_Law1 (Colin Law)]

Unless I am missing something (which is very likely) I do not see the need for the MyProducts table. What is wrong with just

User has_many locations Product has_many locations Location belongs_to user belongs_to user

Then a user has a number of locations, each of which may have an associated product (or not). Each product can appear in many or no locations.

Colin

[Mike27 (Mike)]

Unless I am missing something (which is very likely) I do not see the need for the MyProducts table. What is wrong with just

User    has_many locations Product   has_many locations Location   belongs_to user   belongs_to user

Then a user has a number of locations, each of which may have an associated product (or not). Each product can appear in many or no locations.

Colin

Hi there,

I have some complex situation to solve, and can't manage to find a way which satisfy me ...

Here's the problem :

You have to handle many Users (id, name, email, password). You have a list of many Products (id, name) which are the same for all users. You have some Locations (id, user_id, name) of where to put one product, each user defining his own locations.

BUT

Every user should be able to put his very own "physical instance" of one product in a location OR NOT, which one will, consequently, be different for every user. Moreover, he may specify an alternative name for the product.

So you have to make some model/table that can link product, location, and user altogether. Let's call it MyProducts.

IMO there is 2 ways to go, based on the above : - either you put only the products that have a location in MyProducts - or you duplicate (badbadbad!) all the products from Products in MyProducts, and so for each user, which force you to maintain the same list in both tables, but users and products won't change too often, and it will require less work when you have to know which product has been "modified" or not.

My way of solving this for the moment is the first one :

You have one Product model, that has_many user_products You have one User model, that has_many user_products You have one Location model, that has_many user_products You have one MyProduct model, that belongs_to Product, belongs_to Location, and belongs_to User

This doesn't seem too bad, does it ?

The problem is, in your index view, when you want to list all Products, you have to get an array of all products, and an array of all my_products, and then subtract the products that exist in user_product from the products array, so you get only the product not "modified" by the user, you can display them, and you can then display those in user_product. But they're not ordered. So maybe there is some more work to do so ...

And this looks ugly IMO.

So that's why I'm asking you, how would you do something like that ? Is it a good idea to do as I did ? This looks like a three way association, and I've been taught to never do that but when you can't do anything else.

And above all, is there some Rails-way to do this ? Like using has_and_belongs_to_many in some cases.

PS : I hope my English isn't too bad, I did my best

>

>

[Mike27 (Mike)]

Unless I am missing something (which is very likely) I do not see the need for the MyProducts table. What is wrong with just

User    has_many locations Product   has_many locations Location   belongs_to user   belongs_to user

Then a user has a number of locations, each of which may have an associated product (or not). Each product can appear in many or no locations.

Colin

Hi there,

I have some complex situation to solve, and can't manage to find a way which satisfy me ...

Here's the problem :

You have to handle many Users (id, name, email, password). You have a list of many Products (id, name) which are the same for all users. You have some Locations (id, user_id, name) of where to put one product, each user defining his own locations.

BUT

Every user should be able to put his very own "physical instance" of one product in a location OR NOT, which one will, consequently, be different for every user. Moreover, he may specify an alternative name for the product.

So you have to make some model/table that can link product, location, and user altogether. Let's call it MyProducts.

IMO there is 2 ways to go, based on the above : - either you put only the products that have a location in MyProducts - or you duplicate (badbadbad!) all the products from Products in MyProducts, and so for each user, which force you to maintain the same list in both tables, but users and products won't change too often, and it will require less work when you have to know which product has been "modified" or not.

My way of solving this for the moment is the first one :

You have one Product model, that has_many user_products You have one User model, that has_many user_products You have one Location model, that has_many user_products You have one MyProduct model, that belongs_to Product, belongs_to Location, and belongs_to User

This doesn't seem too bad, does it ?

The problem is, in your index view, when you want to list all Products, you have to get an array of all products, and an array of all my_products, and then subtract the products that exist in user_product from the products array, so you get only the product not "modified" by the user, you can display them, and you can then display those in user_product. But they're not ordered. So maybe there is some more work to do so ...

And this looks ugly IMO.

So that's why I'm asking you, how would you do something like that ? Is it a good idea to do as I did ? This looks like a three way association, and I've been taught to never do that but when you can't do anything else.

And above all, is there some Rails-way to do this ? Like using has_and_belongs_to_many in some cases.

PS : I hope my English isn't too bad, I did my best

>

>

[Jeremy1 (Jérémy)]

You actually are missing something, but I should have been more clear on that part.

So, the hard point is that there is a generic list of products, shared by all users. BUT this list is only for referencing purpose, as far as a user may want a "modified" version of a product in this list.

Moreover, a "modified" product is not only a product associated to a location, but it may have alternative captions as well.

An example may be more explicit : Imagine you have 3 products, A, B, and C And you have 2 users : John and Sally And John have one location in his store : LocationJ And Sally have one location in her store : LocationS And John have put the product A in LocationJ And Sally have put the product B in LocationS

When John wants to see the products list, he should see : Code | Caption | Location | AlternativeCaption   A | The A Product | LocationJ | The Alt. A Product ==> But actually, in this table, the location is only an ID, pointing to a location in the location table   B | The B Product | |   C | The C Product | |

And Sally should see : Code | Caption | Location | AlternativeCaption   A | The A Product | |   B | The B Product | LocationS | The Alt. B Product   C | The C Product | |

So ok, I may use your model and put the alternative captions in the Location table, but then it's not very relevant