How to relate data correctly? - sql

Question

I have this database where I am storing clothes from different retailers:
So each product has different colors
Each product also has different sizes
Each size has also different colors
Now for each product and for each different size and color, there could be different prices.
I am using Django for this, and I am asking any thoughts on how this database relation might work out.
Would I have something like this?
class Product(models.Model):
name = model.CharField()
class Size(models.Model):
size_of_product = model.CharField()
product = model.ForeignKey(Product)
class Color(models.Model):
color_of_product = model.CharField()
product = model.ForeignKey(Product)
size = model.ManyToManyField(Size,though="Price")
class price(model.Model):
size = model.ForeignKey(Size)
color = model.ForeignKey(Color)
date =model.Date()
Could anyone please suggest me of a better solution because obviously I don't have much practice with databases yet?
Thank You!

Answer 1

I propose the following to be close with your initial design:
class Product(models.Model):
name = models.CharField()
class Size(models.Model):
size_of_product = models.CharField()
class Color(models.Model):
color_of_product = models.CharField()
class ProductPrice(model.Model):
size = models.ForeignKey(Size)
color = models.ForeignKey(Color)
product = modelss.ForeignKey(Product)
price = models.DecimalField(...)
With that you'll have a list of products, a list of sizes and a list of colors. Whenever you want to add a variation for a product, you'll just a new ProductPrice instance with the price of the combination of all three (product, size, color) instances.
However, as a general comment, most e-shops do not work like this since products have more characteristics than color or size (for example manufacturer or material).
So, a more general solution would be to have a Category model that defines different categories of things (f.e shoes, jackets, trousers). Each Category has a number of Characteristics (for example color or material) and each Characteristic has a number of possible Values (for example blue, brown or leather, cotton etc). Finally, your Product which will be a specific item with a price, will belong to a specific Category and have specific Values for each of the Characteristics of that Category.
class Characteristic(models.Model):
name = modes.CharField()
class Category(models.Model):
name = modes.CharField()
# Each Category can have many characteristics and each
# characteristic may be related to many categories (e.g
# both shoes and jackets have color
characteristics = models.ManyToManyField(Characteristic)
class Value(models.Model):
value = models.CharField()
# each value belongs to a specific characteristic
characteristic = models.ForeignKey(Characteristic)
class Product(models.Model):
category = models.ForeignKey(Category)
# A product will have a number of values (e.g brown, leather)
values = models.ManyToManyField(Value)
prices = models.DecimalField()
So using the above design we can support as many characteristics as we want for each of our Products.

Answer 2

Ok, so you're modeling clothing. (Pun absolutely intended!) Fine, let's see what we can do about that.
Each product has different colors
Fine. The entity product has an attribute color. Let's continue.
Each product also has different sizes
Fine again. The entity product has an attribute size. So far so good.
Each size has also different colors
Um. Hold on. While a product may have a size and a color, a size cannot have a color nor a color have a size. As attributes, these relate to product, not to each other. Your modeling breaks down at this point.
I think what you mean is that all colors are not available in all sizes. This is different. In this case, a color is not directly related to a product, but a product/size combination.
You have correctly identified this as a many-to-many relationship. But it is between color and an intermediate product/size combination, not directly to product.