Hi, I'm trying to create a three-way relationship (Googling turned up some interesting results..), but can't quite figure it out.

What I have are three models; Application, Product, and ProductMode.

• A Product belongsToMany ProductModes (I have this relationship working).
• A ProductMode belongsToMany Products (I have this relationship working).
• An Application belongsToMany Products and one (Or more) of the Product's ProductModes. This is what I'm stuck on.

When creating an Application, you need to be able to choose a series of Products and a ProductMode to link it to. An Application could link to the same Product multiple times, but with a different ProductMode. An Application could link to the same ProductMode multiple times, but with a different Product. In the three-way relationship, the Application and Product are mandatory, but the ProductMode is optional, as not all Products have a ProductMode.

I currently have a DB schema like so:

For the base tables:

applications

| id | name           |
|----|----------------|
| 1  | Application 01 |
| 2  | Application 02 |

products

| id | name       |
|----|------------|
| 1  | Product 01 |
| 2  | Product 02 |

product_modes

| id | name    |
|----|---------|
| 1  | Mode 01 |
| 2  | Mode 02 |

For the pivot table (All three columns are the Primary key):

| application_id | product_id | product_mode_id |
|----------------|------------|-----------------|
| 1              | 1          | 1               |
| 1              | 1          | 2               |
| 1              | 2          | 1               |
| 2              | 1          | 2               |

The problem is that I can'y figure out how to get the relationship working between three models, especially when it comes to populating the pivot table. I did try creating the relationship between only the Application and Product, and having the ProductMode's ID as just pivot data, but then I had issues with the model selector (In the backend form) not showing a Product that I already chosen, if I wanted to add it again for a different ProductMode.

All I'm actually trying to achieve is, on the frontend, to have a set of hyperlinks from an Application to a page to view information on the Product and the ProductMode. And vice-versa, if you're on a page for a Product and ProductMode, that has linked Applications, it displays a series of links back to the Application.

Any advice would be greatly appreciated.

Last updated 8 years ago

Hi, When you need to have complicated relations, you should create additional models for pivot tables and use them to create relations.

In your case, I would create model ApplicationProductMode for pivot table (and add id column as primary key in pivot table).

So, relations would be:

• Application hasMany ApplicationProductMode.
• ApplicationProductMode belongsTo Product and belongsTo ProductMode.

So, you can get ApplicationProductMode's of Application and then get Product data (name) and Mode data (name) from relations between ApplicationProductMode and Product and ProductMode.

Last updated 8 years ago

Hi Eugene.

Thanks very much! I tried creating a Pivot model, but couldn't quite figure it out, but your explanation makes it much clearer. I've implemented it and it seems to be working perfectly.