Elixir db model

Question

I have designed this model which is very flexible. For example, you can create asset types, assets and combinations of them infinitely. It is the front end to a Python Pyramid website, so all the validation and business logic is handled by the web app.

However, not being a db guy, I have this sneaking suspicion that the schema totally sucks. There may be performance issues etc that I haven't foreseen etc.

class Asset(Entity):
    has_field('TimeStamp', Unicode, nullable=False)
    has_field('Modified', Unicode)
    belongs_to('AssetType', of_kind='AssetType', inverse='Assets')
    has_many('Values', of_kind='Value', inverse='Asset')
    Assets = ManyToMany('Asset')

    @property  
    def Label(self):
        if self.AssetType:
            for f in self.AssetType.Fields:
                if f.Label:
                    if self.Values:
                        for v in self.Values:
                            if v.Field.Name == f.Name:
                                return v.Value

    def __repr__(self):
        return '<Asset | %s>' % self.id

class AssetType(Entity):
    has_field('Name', Unicode, primary_key=True)
    has_field('Plural', Unicode)
    has_many('Assets', of_kind='Asset', inverse='AssetType')
    has_many('Fields', of_kind='Field', inverse='AssetType')

class Value(Entity):
    has_field('Value', Unicode)
    belongs_to('Asset', of_kind='Asset', inverse='Values')
    belongs_to('Field', of_kind='Field', inverse='Values')

class Field(Entity):
    has_field('Name', Unicode)
    has_field('Unique', Unicode, default=False)
    has_field('Label', Boolean, default=False)
    has_field('Searchable', Boolean, default=False)
    has_field('Required', Boolean, default=False)
    has_many('Values', of_kind='Value', inverse='Field')
    belongs_to('FieldType', of_kind='FieldType', inverse='Fields')
    belongs_to('AssetType', of_kind='AssetType', inverse='Fields')

class FieldType(Entity):
    has_field('Name', Unicode, primary_key=True)
    has_field('Label', Unicode, unique=True)
    has_many('Fields', of_kind='Field', inverse='FieldType')

Answer 1

You've reinvented a database inside a database. Basically, the Asset/AssetType is a simulation of a database inside a database which will as a result be slow. Also, you are going to spend a lot of effort reimplementing database features.

You could do this by using a NoSQL database which is designed to handle less structured data might be a good idea. Or you could create a table for each asset type which will perform better.

@property  
def Label(self):
    if self.AssetType:
        for f in self.AssetType.Fields:
            if f.Label:
                if self.Values:
                    for v in self.Values:
                        if v.Field.Name == f.Name:
                            return v.Value

That's really nested which is bad sign. I suggest something like:

@property
def Label(self):
    if self.AssetType:
       label = self.AssetType.Label
       field = self.find_field(label)
       if field:
           return field.Value

Or if you use the Null Object pattern:

@property
def Label(self):
    return self.find_field(self.AssetType.label).Value