Extends the syntax of defclass to allow special slots to be mapped onto the attributes of database views.
A class name.
The superclasses of the class to be created.
The slot definitions of the new class.
The class options of the new class.
The slot options for def-view-class are :db-kind and :db-info . In addition the slot option :type is treated specially for view classes.
:db-kind may be one of :base , :key , :join , or :virtual . The default is :base . Each value is described below:
This indicates that this slot corresponds to an ordinary attribute of the database view. You can name the database attribute by using the keyword :column . By default, the database attribute is named by the slot.
This indicates that this slot corresponds to part of the unique key for this view. A :key slot is also a :base slot.
This indicates that this slot corresponds to a join. A slot of this type will contain view class objects.
This indicates that this slot is an ordinary CLOS slot not associated with a database column.
A join is defined by the slot option :db-info , which takes a list. Items in the list may be:
This is the slot of the defining class to be a subject for the join. The argument slot-name may be an element or a list of elements, where elements can be symbols, nil , strings, integers or floats.
This is the name of the slot of the :join-class to be a subject for the join. The slot-name may be an element or a list of elements, where elements can be symbols, nil , strings, integers or floats.
This is the name of a :join slot in :join-class . This is optional and is only specified if you want the defining slot to be filled with instances of this target-slot as opposed to those of :join-class . An example of its usage is when the :join-class is an intermediate class and you are really only interested in it as a route to the :target slot.
Defers filling this slot from the database until the slot itself is accessed.
This is the opposite of :deferred and generates the join SQL for this slot whenever a query is generated on the class. In other words, this is an intermediate class only, which is present for the purpose of joining two entities of other classes together. The :immediate specification for :retrieval also defines :set nil .
The slot will contain a list of pairs of instances, one of which is the target instance (if specified) and one is the join instance.
The slot will contain a single instance.
The syntax for :home-key and :foreign-key means that an object from a join class will only be included in the join slot if the values from the home-key are equal to the values in the foreign-key, in order. These values are calculated as follows: if the element in the list is a symbol it is taken to be a slot name and the value of the slot is used, otherwise the element is taken to be the value. See the second example below.
The :type slot option is treated specially for view-classes. There is a need for stringent type-checking in view-classes because of the translation into database data. Some methods are provided for type checking and type conversion. For example, a :type specifier of (string 10) in SQL terms means allow a character type value with length of less than or equal to 10.
A class-option for def-view-class is :base-table , which is the name of the table corresponding to the class. If you do not specify it, it defaults to the name of the class.
The macro def-view-class creates a class called name which maps onto a database view. The macro def-view-class extends the syntax of defclass to allow special base slots to be mapped onto the attributes of database views (presently single tables). When a select query that names a view-class is submitted, then the corresponding database view is queried, and the slots in the resulting view-class instances are filled with attribute values from the database.
One of the default classes for superclasses is standard-db-object .
The following example shows a class corresponding to the traditional employees table, with the employee's department given by a join with the departments table.
(def-view-class employee (standard-db-object)
((employee-number :db-kind :key
:column empno
:type integer)
(employee-name :db-kind :base
:column ename
:type (string 20)
:accessor employee-name)
(employee-department :db-kind :base
:column deptno
:type integer
:accessor employee-department)
(employee-job :db-kind :base
:column job
:type (string 9))
(employee-manager :db-kind :base
:column mgr
:type integer)
(employee-location :db-kind :join
:db-info (:join-class department
:retrieval :deferred
:set nil
:home-key
employee-department
:foreign-key
department-number
:target-slot
department-loc)
:accessor employee-location))
(:base-table emp))
The following example illustrates how elements or lists of elements can follow :home-key and :foreign-key in the :db-info slot option.
(def-view-class flex-schema ()
((name :type (string 8) :db-kind :key)
(description :type (string 256))
(classes :db-kind :join
:db-info (:home-key name
:foreign-key schema-name
:join-class flex-class
:retrieval :deferred)))
(:base-table flex_schema))
(def-view-class flex-class ()
((schema-name :type (string 8) :db-kind :key
:column schema_name)
(name :type (string 32) :db-kind :key)
(base-name :type (string 64) :column base_name)
(super-classes :db-kind :join
:db-info (:home-key
(schema-name name)
:foreign-key
(schema-name class-name)
:join-class
flex-superclass
:retrieval :deferred))
(schema :db-kind :join
:db-info (:home-key schema-name
:foreign-key name
:join-class flex-schema
:set nil))
(properties :db-kind :join
:db-info (:home-key (schema-name name "")
:foreign-key
(schema-name class-name slot-name)
:join-class flex-property
:retrieval :deferred)))
(:base-table flex_class))
(def-view-class flex-slot ()
((schema-name :type (string 8) :db-kind :key
:column schema_name)
(class-name :type (string 32) :db-kind :key
:column class_name)
(name :type (string 32) :db-kind :key)
(class :db-kind :join
:db-info (:home-key (schema-name class-name)
:foreign-key (schema-name name)
:join-class flex-class
:set nil))
(properties :db-kind :join
:db-info (:home-key
(schema-name class-name name)
:foreign-key
(schema-name class-name slot-name)
:join-class flex-property
:retrieval :deferred)))
(:base-table flex_slot))
(def-view-class flex-property ()
((schema-name :type (string 8) :db-kind :key
:column schema_name)
(class-name :type (string 32) :db-kind :key
:column class_name)
(slot-name :type (string 32) :db-kind :key
:column slot_name)
(property :type (string 32) :db-kind :key)
(values :db-kind :join
:db-info (:home-key
(schema-name class-name
slot-name property)
:foreign-key
(schema-name class-name
slot-name property)
:join-class flex-property-value
:retrieval :deferred)))
(:base-table flex_property))
(def-view-class flex-property-value ()
((schema-name :type (string 8) :db-kind :key
:column schema_name)
(class-name :type (string 32) :db-kind :key
:column class_name)
(slot-name :type (string 32) :column slot_name)
(property :type (string 32) :db-kind :key)
(order :type integer)
(value :type (string 128)))
(:base-table flex_property_value))