What is the best practice to store a specification of an Entity in Spring? - spring

Question

My database contain products in a single table called Product, and each product might have certain fields with their specification, e.g.
//Bicycle product
{
"name" : "Bicycle",
"category" : "Bicycles"
"specification" : {
"color" : "red"
}
}
//Wheel product
{
"name" : "Wheel",
"category" : "Spare Parts",
"specification" : {
"diameter" : "7.5"
}
}
So i've come up with idea of making a field of type Map<String, String> (which creates a another table called specifications) in my Product entity to contain those specifications. But i don't like this approach, because all of the additional fields would be of String type, and because Spring will create a bean out of this field, I wont be able to specify the type of value as an abstract class (like this Map<String, Object>).
I thought of creating additional fields, like this:
#ElementCollection
private Map<String, String> string_features;
#ElementCollection
private Map<String, Double> double_features;
// ...
But it looks kind of ugly and I think there is a better way to do it. And also, if the specification field is of a different Entity type, I will have to create another map for that specific entity, e.g.
//Bicycle product
{
"name" : "Bicycle",
"category" : "Bicycles"
"specification" : {
"color" : "red",
"wheel" : {
"name" : "Wheel",
}
}
}

Answer 1

If the value can be only be numbers and strings, maybe you can save the value as strings and then use a regex to check if the string is a number before returning the value.
Otherwise, you need a way to recognize the type.
I think I would change it to this:
//Bicycle product
{
"name" : "Bicycle",
"category" : "Bicycles"
"specifications" : [
{ name: "color", value: "red", type: "string"},
{ name: "diameter", value: "7.5", type: "double"},
...
]
}
You can map it as:
#ElementCollection
private List<Specification> specifications;
...
#Embaddable
class Specification {
String name;
String value;
String type;
// ... getter/setter and everything else
#Transient
Object getConvertedValue() {
if ("double".equals(type)) {
return Double.parse(value);
}
// String is the default
return value;
}
}
The nice thing is that you can have as many types as you want.