1 

     2 .. _FetchAttrs:

     3 

     4 Loaded attributes and default sorting management

     5 ````````````````````````````````````````````````

     6 

     7 * The class attribute `fetch_attrs` allows to define in an entity class a list

     8   of names of attributes or relations that should be automatically loaded when

     9   entities of this type are fetched from the database. In the case of relations,

    10   we are limited to *subject of cardinality `?` or `1`* relations.

    11 

    12 * The class method `fetch_order(attr, var)` expects an attribute (or relation)

    13   name as a parameter and a variable name, and it should return a string

    14   to use in the requirement `ORDERBY` of an RQL query to automatically

    15   sort the list of entities of such type according to this attribute, or

    16   `None` if we do not want to sort on the attribute given in the parameter.

    17   By default, the entities are sorted according to their creation date.

    18 

    19 * The class method `fetch_unrelated_order(attr, var)` is similar to

    20   the method `fetch_order` except that it is essentially used to

    21   control the sorting of drop-down lists enabling relations creation

    22   in the editing view of an entity. The default implementation uses

    23   the modification date. Here's how to adapt it for one entity (sort

    24   on the name attribute): ::

    25 

    26    class MyEntity(AnyEntity):

    27        __regid__ = 'MyEntity'

    28        fetch_attrs = ('modification_date', 'name')

    29 

    30        @classmethod

    31        def fetch_unrelated_order(cls, attr, var):

    32            if attr == 'name':

    33               return '%s ASC' % var

    34            return None

    35 

    36 

    37 The function `fetch_config(fetchattrs, mainattr=None)` simplifies the

    38 definition of the attributes to load and the sorting by returning a

    39 list of attributes to pre-load (considering automatically the

    40 attributes of `AnyEntity`) and a sorting function based on the main

    41 attribute (the second parameter if specified, otherwise the first

    42 attribute from the list `fetchattrs`). This function is defined in

    43 `cubicweb.entities`.

    44 

    45 For example: ::

    46 

    47   class Transition(AnyEntity):

    48     """..."""

    49     __regid__ = 'Transition'

    50     fetch_attrs, fetch_order = fetch_config(['name'])

    51 

    52 Indicates that for the entity type "Transition", you have to pre-load

    53 the attribute `name` and sort by default on this attribute.