Changes between Version 3 and Version 4 of S3/S3Model/SuperEntities

Timestamp:

11/01/10 23:35:16 (14 years ago)

Author:

Dominic König

Comment:

--

S3/S3Model/SuperEntities

@@ -3 +3 @@
 = S3 Super-Entities =
 
-  - ''coming soon...''
+== Introduction ==
+
+Sometimes it is useful to share the same component among multiple resources. To realize this, S3XRC uses link tables - so-called ''Super-Entities''.
+
+  - ''code examples to follow...''
+
 [[Image(superentity.png)]]
+
+Instead of having several foreign keys for different primary resources, the shared component contains only one foreign key for the link table.
+
+The primary resource (=instance table) contains the same ''super-key'' field as the component, thus the forward join of resource-to-component can be established as a natural join, i.e. without accessing the link table.
+
+For the (seldom needed) backward join component-to-resource, the link table needs to be involved because it contains the table name of the primary resource in the field {{instance_type}}.
+
+Disadvantage of the link table method is that the link table needs to be updated whenever a primary resource record is created, updated or deleted. Thus, it is recommended to not use super-entities for resources where the extra load on write can give a serious performance problem (e.g. messages), or at least to keep the super-entity table lean and free of extra references.
+
+== API ==
+
+Too simplify the handling of super-entities in the model, S3Model provides a unified API for super-entities:
+
+=== Defining a Super-Entity ===
+
+To define a super-entity, you can use the {{{super_entity()}}} function:
+
+You can define so-called ''shared fields'' in the super-entity, which are mirrored from the respective resource record. This allows to easily access these data from the component without the need to involve the primay instance table in the backward-join:
+
+In case the names of the shared fields in your instance table differ from those of the super-entity, you can define a field mapping:
+
+=== Defining an Instance of a Super-Entity ===
+
+To make a table an instance of a super-entity, you can use {{{s3xrc.model.configure()}}}:
+
+In case your table uses different names for the shared fields, you can additionally set a field mapping:
+
+=== Linking to a Super-Entity ===
+
+Both, instance tables as well as shared components need to be linked to the super-entity. This can be done by inserting a ''super-key'' field into the instance/component table which must have the same name as the primary key of the super-entity. You can use the {{{super_link()}}} function as a DRY method for this:
+
+=== Updating a Super-Entity ===
+
+If you use [wiki:S3XRC/RESTfulAPI/s3_rest_controller s3_rest_controller()] for CRUD, it will automatically create, update and delete super-entities as necessary.
+
+Otherwise, or if you manipulate records outside s3_rest_controller, you have to update all super-entities which an instance table implements whenever you create, update or delete a record in that table.
+
+To do this, you can use:
+{{{
+s3xrc.model.update_super(table, record)
+}}}
+
+where {{{table}}} is the instance table and {{{record}}} the newly created/updated record.
+
+In case you're going to delete a record from an instance table, you may use:
+{{{
+s3xrc.model.delete_super(table, record)
+}}}
+
+'''before''' you delete the record, where {{{table}}} is the instance table and {{{record}}} the record to be deleted.
 
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