Хотя это невозможно сделать полностью реляционно, вы все же можете немного нормализовать свои таблицы и немного упростить программирование.
У вас могут быть такие таблицы:
-- what are the products?
Products (Id, ProductTypeId, Name)
-- what kind of product is it?
ProductTypes (Id, Name)
-- what attributes can a product have?
Attributes (Id, Name, ValueType)
-- what are the attributes that come with a specific product type?
ProductTypeAttributes (Id, ProductTypeId, AttributeId)
-- what are the values of the attributes for each product?
ProductAttributes (ProductId, ProductTypeAttributeId, Value)
Итак, для телефона и телевизора:
ProductTypes (1, Phone) -- a phone type of product
ProductTypes (2, TV) -- a tv type of product
Attributes (1, ScreenSize, integer) -- how big is the screen
Attributes (2, Has4G, boolean) -- does it get 4g?
Attributes (3, HasCoaxInput, boolean) -- does it have an input for coaxial cable?
ProductTypeAttributes (1, 1, 1) -- a phone has a screen size
ProductTypeAttributes (2, 1, 2) -- a phone can have 4g
-- a phone does not have coaxial input
ProductTypeAttributes (3, 2, 1) -- a tv has a screen size
ProductTypeAttributes (4, 2, 3) -- a tv can have coaxial input
-- a tv does not have 4g (simple example)
Products (1, 1, CoolPhone) -- product 1 is a phone called coolphone
Products (2, 1, AwesomePhone) -- prod 2 is a phone called awesomephone
Products (3, 2, CoolTV) -- prod 3 is a tv called cooltv
Products (4, 2, AwesomeTV) -- prod 4 is a tv called awesometv
ProductAttributes (1, 1, 6) -- coolphone has a 6 inch screen
ProductAttributes (1, 2, True) -- coolphone has 4g
ProductAttributes (2, 1, 4) -- awesomephone has a 4 inch screen
ProductAttributes (2, 2, False) -- awesomephone has NO 4g
ProductAttributes (3, 3, 70) -- cooltv has a 70 inch screen
ProductAttributes (3, 4, True) -- cooltv has coax input
ProductAttributes (4, 3, 19) -- awesometv has a 19 inch screen
ProductAttributes (4, 4, False) -- awesometv has NO coax input
Причина, по которой это не является полностью реляционным, заключается в том, что вам все равно нужно оценить тип значения (bool, int и т. д.) атрибута, прежде чем вы сможете использовать его осмысленным образом в своем коде.
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Forklift
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15.02.2017