--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/doc/book/en/B030-data-as-objects.en.txt Tue Dec 23 13:15:23 2008 -0800
@@ -0,0 +1,144 @@
+.. -*- coding: utf-8 -*-
+
+
+Stored data handling
+====================
+
+Classes `Entity` and `AnyEntity`
+--------------------------------
+
+To provide a specific behavior for each entity, we just need to define
+a class inheriting from `cubicweb.entities.EnyEntity`. In genera, we have
+to defined those classes in a module of `entites` package of an application
+so that it will be available on both server and client side.
+
+The class `AnyEntity` is loaded dynamically from the class `Entity`
+(`cubciweb.common.entity`). We define a sub-class to add methods or to
+specialize the handling of a given entity type
+
+Descriptors are added when classes are registered in order to initialize the class
+according to its schema:
+
+* we can access the defined attributes in the schema thanks the attributes of
+ the same name on instances (typed value)
+
+* we can access the defined relations in the schema thanks to the relations of
+ the same name on instances (entities instances list)
+
+The methods defined for `AnyEntity` or `Entity` are the following ones:
+
+* `has_eid()`, returns true is the entity has an definitive eid (e.g. not in the
+ creation process)
+
+* `check_perm(action)`, checks if the user has the permission to execcute the
+ requested action on the entity
+
+:Formatting and output generation:
+
+ * `view(vid, **kwargs)`, apply the given view to the entity
+
+ * `absolute_url(**kwargs)`, returns an absolute URL to access the primary view
+ of an entity
+
+ * `rest_path()`, returns a relative REST URL to get the entity
+
+ * `format(attr)`, returns the format (MIME type) of the field given un parameter
+
+ * `printable_value(attr, value=_marker, attrtype=None, format='text/html')`,
+ returns a string enabling the display of an attribute value in a given format
+ (the value is automatically recovered if necessarry)
+
+ * `display_name(form='')`, returns a string to display the entity type by
+ specifying the preferred form (`plural` for a plural form)
+
+:Data handling:
+
+ * `as_rset()`, converts the entity into an equivalent result set simulating the
+ request `Any X WHERE X eid _eid_`
+
+ * `complete(skip_bytes=True)`, executes a request that recovers in one time
+ all the missing attributes of an entity
+
+ * `get_value(name)`, returns the value associated to the attribute name given
+ in parameter
+
+ * `related(rtype, x='subject', limit=None, entities=False)`, returns a list
+ of entities related to the current entity by the relation given in parameter
+
+ * `unrelated(rtype, targettype, x='subject', limit=None)`, returns a result set
+ corresponding to the entities not related to the current entity by the
+ relation given in parameter and satisfying its constraints
+
+ * `set_attributes(**kwargs)`, updates the attributes list with the corresponding
+ values given named parameters
+
+ * `copy_relations(ceid)`, copies the relations of the entities having the eid
+ given in the parameters on the current entity
+
+ * `last_modified(view)`, returns the date the object has been modified
+ (used by HTTP cache handling)
+
+ * `delete()` allows to delete the entity
+
+:Standard meta-data (Dublin Core):
+
+ * `dc_title()`, returns a unicode string corresponding to the meta-data
+ `Title` (used by default the first attribute non-meta of the entity
+ schema)
+
+ * `dc_long_title()`, same as dc_title but can return a more
+ detailled title
+
+ * `dc_description(format='text/plain')`, returns a unicode string
+ corresponding to the meta-data `Description` (look for a description
+ attribute by default)
+
+ * `dc_authors()`, returns a unicode string corresponding to the meta-data
+ `Authors` (owners by default)
+
+ * `dc_date(date_format=None)`, returns a unicode string corresponding to
+ the meta-data `Date` (update date by default)
+
+:Vocabulary control on relations:
+
+ * `vocabulary(rtype, x='subject', limit=None)`, called by the
+ editing views, it returns a list of couples (label, eid) of entities
+ that could be related to the entity by the relation `rtype`
+ * `subject_relation_vocabulary(rtype, limit=None)`, called internally
+ by `vocabulary` in the case of a subject relation
+ * `object_relation_vocabulary(rtype, limit=None)`, called internally
+ by `vocabulary` in the case of an object relation
+ * `relation_vocabulary(rtype, targettype, x, limit=None)`, called
+ internally by `subject_relation_vocabulary` and `object_relation_vocabulary`
+
+
+*rtags*
+-------
+
+*rtags* allows to specify certain behaviors of relations relative to a given
+entity type (see later). They are defined on the entity class by the attribute
+`rtags` which is a dictionnary with as its keys the triplet ::
+
+ <relation type>, <target entity type>, <context position ("subject" ou "object")>
+
+and as the values a `set` or a tuple of markers defining the properties that
+apply to this relation.
+
+It is possible to simplify this dictionnary:
+
+* if we want to specifiy a single marker, it is not necessarry to
+ use a tuple as the value, the marker by itself (characters string)
+ is enough
+* if we only care about a single type of relation and not about the target
+ and the context position (or when this one is not ambigous), we can simply
+ use the name of the relation type as the key
+* if we want a marker to apply independently from the target entity type,
+ we have to use the string `*` as the target entity type
+
+
+Please note that this dictionnary is *treated at the time the class is created*.
+It is automatically merged with the parent class(es) (no need to copy the
+dictionnary from the parent class to modify it). Also, modify it after the
+class is created will not have any effect...
+
+.. include:: B051-define-entities.en.txt