1Rose::DB::Object::MetadUastear::CFoonrteriigbnuKteeydR(o3Ps)eer:l:DDBo:c:uOmbejnetcatt:i:oMnetadata::ForeignKey(3)
2
6 Rose::DB::Object::Metadata::ForeignKey - Foreign key metadata.
7
9 use Rose::DB::Object::Metadata::ForeignKey;
10 $fk = Rose::DB::Object::Metadata::ForeignKey->new(...);
12 $fk->make_methods(...);
13 ...
14
16 Objects of this class store and manipulate metadata for foreign keys in
17 a database table. It stores information about which columns in the
18 local table map to which columns in the foreign table.
19 This class will create methods for "the thing referenced by" the
21 foreign key column(s). You'll still need accessor method(s) for the
22 foreign key column(s) themselves.
23 Both the local table and the foreign table must have
25 Rose::DB::Object-derived classes fronting them.
26 Foreign keys can represent both "one to one" and "many to one"
28 relationships. To choose, set the relationship_type attribute to
29 either "one to one" or "many to one". The default is "many to one".
30 MAKING METHODS
32 A Rose::DB::Object::Metadata::ForeignKey-derived object is responsible
33 for creating object methods that manipulate objects referenced by a
34 foreign key. Each foreign key object can make zero or more methods for
35 each available foreign key method type. A foreign key method type
36 describes the purpose of a method. The default list of foreign key
37 method types contains only one type:
38 "get_set"
40 A method that returns the object referenced by the foreign key.
41 Methods are created by calling make_methods. A list of method types
43 can be passed to the call to make_methods. If absent, the list of
44 method types is determined by the auto_method_types method. A list of
45 all possible method types is available through the
46 available_method_types method.
47 These methods make up the "public" interface to foreign key method
49 creation. There are, however, several "protected" methods which are
50 used internally to implement the methods described above. (The word
51 "protected" is used here in a vaguely C++ sense, meaning "accessible to
52 subclasses, but not to the public.") Subclasses will probably find it
53 easier to override and/or call these protected methods in order to
54 influence the behavior of the "public" method maker methods.
55 A Rose::DB::Object::Metadata::ForeignKey object delegates method
57 creation to a Rose::Object::MakeMethods-derived class. Each
58 Rose::Object::MakeMethods-derived class has its own set of method
59 types, each of which takes it own set of arguments.
60 Using this system, four pieces of information are needed to create a
62 method on behalf of a Rose::DB::Object::Metadata::ForeignKey-derived
63 object:
64 · The foreign key method type (e.g., "get_set")
66 · The method maker class (e.g.,
68 Rose::DB::Object::MakeMethods::Generic)
69 · The method maker method type (e.g., object_by_key)
71 · The method maker arguments (e.g., "interface => 'get_set'")
73 This information can be organized conceptually into a "method map" that
75 connects a foreign key method type to a method maker class and,
76 finally, to one particular method type within that class, and its
77 arguments.
78 The default method map for Rose::DB::Object::Metadata::ForeignKey is:
80 "get_set"
82 Rose::DB::Object::MakeMethods::Generic, object_by_key, "interface
83 => 'get_set'" ...
84 "get_set_now"
86 Rose::DB::Object::MakeMethods::Generic, object_by_key, "interface
87 => 'get_set_now'" ...
88 "get_set_on_save"
90 Rose::DB::Object::MakeMethods::Generic, object_by_key, "interface
91 => 'get_set_on_save'" ...
92 "delete_now"
94 Rose::DB::Object::MakeMethods::Generic, object_by_key, "interface
95 => 'delete_now'" ...
96 "delete_on_save"
98 Rose::DB::Object::MakeMethods::Generic, object_by_key, "interface
99 => 'delete_on_save'" ...
100 Each item in the map is a foreign key method type. For each foreign
102 key method type, the method maker class, the method maker method type,
103 and the "interesting" method maker arguments are listed, in that order.
104 The "..." in the method maker arguments is meant to indicate that
106 arguments have been omitted. Arguments that are common to all foreign
107 key method types are routinely omitted from the method map for the sake
108 of brevity.
109 The purpose of documenting the method map is to answer the question,
111 "What kind of method(s) will be created by this foreign key object for
112 a given method type?" Given the method map, it's possible to read the
113 documentation for each method maker class to determine how methods of
114 the specified type behave when passed the listed arguments.
115 Remember, the existence and behavior of the method map is really
117 implementation detail. A foreign key object is free to implement the
118 public method-making interface however it wants, without regard to any
119 conceptual or actual method map.
120
122 default_auto_method_types [TYPES]
123 Get or set the default list of auto_method_types. TYPES should be
124 a list of foreign key method types. Returns the list of default
125 foreign key method types (in list context) or a reference to an
126 array of the default foreign key method types (in scalar context).
127 The default list contains the "get_set_on_save" and
128 "delete_on_save" foreign key method types.
129
131 available_method_types
132 Returns the full list of foreign key method types supported by this
133 class.
134 auto_method_types [TYPES]
136 Get or set the list of foreign key method types that are
137 automatically created when make_methods is called without an
138 explicit list of foreign key method types. The default list is
139 determined by the default_auto_method_types class method.
140 build_method_name_for_type TYPE
142 Return a method name for the foreign key method type TYPE. The
143 default implementation returns the following.
144 For the method types "get_set", "get_set_now", and
146 "get_set_on_save", the foreign key's name is returned.
147 For the method types "delete_now" and "delete_on_save", the foreign
149 key's name prefixed with "delete_" is returned.
150 Otherwise, undef is returned.
152 class [CLASS]
154 Get or set the class name of the Rose::DB::Object-derived object
155 that encapsulates rows from the table referenced by the foreign key
156 column(s).
157 column_map [HASH | HASHREF]
159 This is an alias for the key_columns method.
160 key_column LOCAL [, FOREIGN]
162 If passed a local column name LOCAL, return the corresponding
163 column name in the foreign table. If passed both a local column
164 name LOCAL and a foreign column name FOREIGN, set the local/foreign
165 mapping and return the foreign column name.
166 key_columns [ HASH | HASHREF ]
168 Get or set a hash that maps local column names to foreign column
169 names in the table referenced by the foreign key. Returns a
170 reference to a hash in scalar context, or a list of key/value pairs
171 in list context.
172 make_methods PARAMS
174 Create object method used to manipulate object referenced by the
175 foreign key. Any applicable column triggers are also added.
176 PARAMS are name/value pairs. Valid PARAMS are:
177 "preserve_existing BOOL"
179 Boolean flag that indicates whether or not to preserve existing
180 methods in the case of a name conflict.
181 "replace_existing BOOL"
183 Boolean flag that indicates whether or not to replace existing
184 methods in the case of a name conflict.
185 "target_class CLASS"
187 The class in which to make the method(s). If omitted, it
188 defaults to the calling class.
189 "types ARRAYREF"
191 A reference to an array of foreign key method types to be
192 created. If omitted, it defaults to the list of foreign key
193 method types returned by auto_method_types.
194 If any of the methods could not be created for any reason, a fatal
196 error will occur.
197 methods MAP
199 Set the list of auto_method_types and method names all at once.
200 MAP should be a reference to a hash whose keys are method types and
201 whose values are either undef or method names. If a value is
202 undef, then the method name for that method type will be generated
203 by calling build_method_name_for_type|/build_method_name_for_type,
204 as usual. Otherwise, the specified method name will be used.
205 method_name TYPE [, NAME]
207 Get or set the name of the relationship method of type TYPE.
208 method_types [TYPES]
210 This method is an alias for the auto_method_types method.
211 name [NAME]
213 Get or set the name of the foreign key. This name must be unique
214 among all other foreign keys for a given Rose::DB::Object-derived
215 class.
216 referential_integrity [BOOL]
218 Get or set the boolean value that determines what happens when the
219 local key columns have defined values, but the object they point to
220 is not found. If true, a fatal error will occur when the methods
221 that fetch objects through this foreign key are called. If false,
222 then the methods will simply return undef. The default is true.
223 rel_type [TYPE]
225 This method is an alias for the relationship_type method described
226 below.
227 relationship_type [TYPE]
229 Get or set the relationship type represented by this foreign key.
230 Valid values for TYPE are "one to one" and "many to one".
231 share_db [BOOL]
233 Get or set the boolean flag that determines whether the db
234 attribute of the current object is shared with the foreign object
235 to be fetched. The default value is true.
236 soft [BOOL]
238 This method is the mirror image of the referential_integrity
239 method. Passing a true is the same thing as setting
240 referential_integrity to false, and vice versa. Similarly, the
241 return value is the logical negation of referential_integrity.
242 type
244 Returns "foreign key".
245 with_column_triggers [BOOL]
247 Get or set a boolean value that indicates whether or not triggers
248 should be added to the key columns in an attempt to keep foreign
249 objects and foreign key columns in sync. Defaults to false.
250
252 These methods are not part of the public interface, but are supported
253 for use by subclasses. Put another way, given an unknown object that
254 "isa" Rose::DB::Object::Metadata::ForeignKey, there should be no
255 expectation that the following methods exist. But subclasses, which
256 know the exact class from which they inherit, are free to use these
257 methods in order to implement the public API described above.
258 method_maker_arguments TYPE
260 Returns a hash (in list context) or reference to a hash (in scalar
261 context) of name/value arguments that will be passed to the
262 method_maker_class when making the foreign key method type TYPE.
263 method_maker_class TYPE [, CLASS]
265 If CLASS is passed, the name of the
266 Rose::Object::MakeMethods-derived class used to create the object
267 method of type TYPE is set to CLASS.
268 Returns the name of the Rose::Object::MakeMethods-derived class
270 used to create the object method of type TYPE.
271 method_maker_type TYPE [, NAME]
273 If NAME is passed, the name of the method maker method type for the
274 foreign key method type TYPE is set to NAME.
275 Returns the method maker method type for the foreign key method
277 type TYPE.
278
280 John C. Siracusa (siracusa@gmail.com)
281
283 Copyright (c) 2010 by John C. Siracusa. All rights reserved. This
284 program is free software; you can redistribute it and/or modify it
285 under the same terms as Perl itself.
286perl v5.30.2 2020R-o0s4e-:0:6DB::Object::Metadata::ForeignKey(3)