properties

This module provides support for defining properties on your entities. It both provides, the Property class which acts as a building block for common properties such as fields and relationships (for those, please consult the corresponding modules), but also provides some more specialized properties, such as ColumnProperty and Synonym. It also provides the GenericProperty class which allows you to wrap any SQLAlchemy property, and its DSL-syntax equivalent: has_property.

has_property

The has_property statement allows you to define properties which rely on their entity’s table (and columns) being defined before they can be declared themselves. The has_property statement takes two arguments: first the name of the property to be defined and second a function (often given as an anonymous lambda) taking one argument and returning the desired SQLAlchemy property. That function will be called whenever the entity table is completely defined, and will be given the .c attribute of the entity as argument (as a way to access the entity columns).

Here is a quick example of how to use has_property.

class OrderLine(Entity):
    has_field('quantity', Float)
    has_field('unit_price', Float)
    has_property('price',
                 lambda c: column_property(
                     (c.quantity * c.unit_price).label('price')))

class camelot.core.orm.properties.ColumnProperty(prop, *args, **kwargs)

A specialized form of the GenericProperty to generate SQLAlchemy column_property‘s.

It takes a function (often given as an anonymous lambda) as its first argument. Other arguments and keyword arguments are forwarded to the column_property construct. That first-argument function must accept exactly one argument and must return the desired (scalar-returning) SQLAlchemy ClauseElement.

The function will be called whenever the entity table is completely defined, and will be given the .c attribute of the table of the entity as argument (as a way to access the entity columns). The ColumnProperty will first wrap your ClauseElement in an “empty” label (ie it will be labelled automatically during queries), then wrap that in a column_property.

class OrderLine(Entity):
    quantity = Field(Float)
    unit_price = Field(Numeric)
    price = ColumnProperty(lambda c: c.quantity * c.unit_price,
                           deferred=True)

Please look at the corresponding SQLAlchemy documentation for details.

class camelot.core.orm.properties.CounterMeta

A simple meta class which adds a _counter attribute to the instances of the classes it is used on. This counter is simply incremented for each new instance.

class camelot.core.orm.properties.DeferredProperty(*args, **kwargs)

Abstract base class for all properties of an Entity that are not handled by Declarative but should be handled after a mapper was configured

class camelot.core.orm.properties.EntityBuilder

Abstract base class for all entity builders. An Entity builder is a class of objects which can be added to an Entity (usually by using special properties or statements) to “build” that entity. Building an entity, meaning to add columns to its “main” table, create other tables, add properties to its mapper, ... To do so an EntityBuilder must override the corresponding method(s). This is to ensure the different operations happen in the correct order (for example, that the table is fully created before the mapper that use it is defined).

create_properties()

Subclasses may override this method to add properties to the involved entity.

create_tables()

Subclasses may override this method to create tables.

class camelot.core.orm.properties.GenericProperty(prop, *args, **kwargs)

Generic catch-all class to wrap an SQLAlchemy property.

class OrderLine(Entity):
    quantity = Field(Float)
    unit_price = Field(Numeric)
    price = GenericProperty(lambda c: column_property(
                     (c.quantity * c.unit_price).label('price')))

class camelot.core.orm.properties.Property(*args, **kwargs)

Abstract base class for all properties of an Entity that are not handled by Declarative but should be handled by EntityMeta before a new Entity subclass is constructed

attach(entity, name)

Attach this property to its entity, using ‘name’ as name.

Properties will be attached in the order they were declared.