Tag: relation

I have an application where the requirements are to show a list of (just for example) car manufacturers. When you click on one of the manufacturers, a list of car models appears. You can then click on the car model to show other information. Each model has a lot of other data associated in several relationships from 1 to many (this is not important, but only to provide some background).

My problem is that one of the manufacturers must be treated as a car model. There will be only one car model under this manufacturer. The following is an example of the current database structure. As you can see, there is a manufacturer of MegaCar and there is only one model under this manufacturer. When you click on the MegaCar manufacturer, you must directly load the MegaCar model instead of displaying the model list.

+ ---------------
| manufacturers |
+ ---------------
| id | name |
+ ----- + --------- +
| 1 | Ford |
+ ----- + --------- +
| 2 | Toyota |
+ ----- + --------- +
| 3 | MegaCar |
+ ----- + --------- +

+ -------------------------------- +
| models |
+ -------------------------------- +
| id | manufacturer_id | name |
+ ---- + ----------------- + --------- +
| 1 | 1 | Focus |
+ ---- + ----------------- + --------- +
| 2 | 1 | Mustang |
+ ---- + ----------------- + --------- +
| 3 | 2 | Camry |
+ ---- + ----------------- + --------- +
| 4 | 2 | Corolla |
+ ---- + ----------------- + --------- +
| 5 | 3 | MegaCar |
+ ---- + ----------------- + --------- +

I'm trying to decide on a database design and application design to represent this relationship. Basically, when someone clicks on the manufacturer's MegaCar, I'll need to load the model page for MegaCar (where models.id = 5), not the manufacturer's page (where Manufacturers.id = 3). I'll have to update the database schema for this. My current line of thinking is to add a isModel Flag to the manufacturers table and my code would look something like this:

object = getSelectedManufacturer ();
if (object.isModel) {
singleModel = query (& # 39;
SELECT MODELS.ID OF MODELS
INNER JOIN manufacturers ON models.manufacturers_id = manufacturers.id
WHERE manufacturers.id = [object.id]
        LIMIT 1
& # 39;)
renderModelPage (singleModel)
}
else {
listOfModels = query (& # 39;
SELECT * FROM models
WHERE models.manufacturer_id = [object.id]
    & # 39;)
renderManufacturerPage (listOfModels) // model list page
}

The problem I have with this is that it can be confusing for other people who see my code. It also seems wrong that the relationship between these tables is one to many, but I'm making an exception for a record.

I had another idea to add a nullable. modelId column to the manufacturers table, but I did not like this for the same reason as the previous one. Also, I've seen some questions and answers here discouraging the use of NULL.

What would be the correct way to design this application?