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1 | # vim: ts=8:sw=4:sts=4:et |
2 | package DBIx::Class::Positioned; |
3 | use strict; |
4 | use warnings; |
5 | use base qw( DBIx::Class ); |
6 | |
7 | =head1 NAME |
8 | |
9 | DBIx::Class::Positioned - Modify the position of objects in an ordered list. |
10 | |
11 | =head1 SYNOPSIS |
12 | |
13 | Create a table for your positionable data. |
14 | |
15 | CREATE TABLE employees ( |
16 | employee_id INTEGER PRIMARY KEY AUTOINCREMENT, |
17 | name TEXT NOT NULL, |
18 | position INTEGER NOT NULL |
19 | ); |
20 | |
21 | In your Schema or DB class add Positioned to the top |
22 | of the component list. |
23 | |
24 | __PACKAGE__->load_components(qw( Positioned ... )); |
25 | |
26 | Specify the column that stores the position number for |
27 | each row. |
28 | |
29 | package My::Employee; |
30 | __PACKAGE__->position_column('position'); |
31 | |
32 | Thats it, now you can change the position of your objects. |
33 | |
34 | #!/use/bin/perl |
35 | use My::Employee; |
36 | |
37 | my $employee = My::Employee->create({ name=>'Matt S. Trout' }); |
38 | |
39 | my $rs = $employee->siblings(); |
40 | my @siblings = $employee->siblings(); |
41 | |
42 | my $sibling; |
43 | $sibling = $employee->first_sibling(); |
44 | $sibling = $employee->last_sibling(); |
45 | $sibling = $employee->previous_sibling(); |
46 | $sibling = $employee->next_sibling(); |
47 | |
48 | $employee->move_previous(); |
49 | $employee->move_next(); |
50 | $employee->move_first(); |
51 | $employee->move_last(); |
52 | $employee->move_to( $position ); |
53 | |
54 | =head1 DESCRIPTION |
55 | |
56 | This module provides a simple interface for modifying the position |
57 | of DBIx::Class objects. |
58 | |
59 | =head1 METHODS |
60 | |
61 | =head2 position_column |
62 | |
63 | __PACKAGE__->position_column('position'); |
64 | |
65 | Sets and retrieves the name of the column that stores the |
66 | positional value of each record. Default to "position". |
67 | |
68 | =cut |
69 | |
70 | __PACKAGE__->mk_classdata( 'position_column' => 'position' ); |
71 | |
72 | =head2 siblings |
73 | |
74 | my $rs = $employee->siblings(); |
75 | my @siblings = $employee->siblings(); |
76 | |
77 | Returns either a result set or an array of all other objects |
78 | excluding the one you called it on. |
79 | |
80 | =cut |
81 | |
82 | sub siblings { |
83 | my( $self ) = @_; |
84 | my $position_column = $self->position_column; |
85 | my $rs = $self->search( |
86 | { $position_column => { '!=' => $self->get_column($position_column) } }, |
87 | { order_by => $self->position_column }, |
88 | ); |
89 | if (wantarray()) { return $rs->all(); } |
90 | else { return $rs; } |
91 | } |
92 | |
93 | =head2 first_sibling |
94 | |
95 | my $sibling = $employee->first_sibling(); |
96 | |
97 | Returns the first sibling object. |
98 | |
99 | =cut |
100 | |
101 | sub first_sibling { |
102 | my( $self ) = @_; |
103 | return ($self->search( |
104 | {}, |
105 | { rows=>1, order_by => $self->position_column }, |
106 | )->all())[0]; |
107 | } |
108 | |
109 | =head2 last_sibling |
110 | |
111 | my $sibling = $employee->last_sibling(); |
112 | |
113 | Return the last sibling. |
114 | |
115 | =cut |
116 | |
117 | sub last_sibling { |
118 | my( $self ) = @_; |
119 | return ($self->search( |
120 | {}, |
121 | { rows=>1, order_by => $self->position_column.' DESC' }, |
122 | )->all())[0]; |
123 | } |
124 | |
125 | =head2 previous_sibling |
126 | |
127 | my $sibling = $employee->previous_sibling(); |
128 | |
129 | Returns the sibling that resides one position higher. Undef |
130 | is returned if the current object is the first one. |
131 | |
132 | =cut |
133 | |
134 | sub previous_sibling { |
135 | my( $self ) = @_; |
136 | my $position_column = $self->position_column; |
137 | return ($self->search( |
138 | { $position_column => { '<' => $self->get_column($position_column) } }, |
139 | { rows=>1, order_by => $position_column.' DESC' }, |
140 | )->all())[0]; |
141 | } |
142 | |
143 | =head2 next_sibling |
144 | |
145 | my $sibling = $employee->next_sibling(); |
146 | |
147 | Returns the sibling that resides one position lower. Undef |
148 | is returned if the current object is the last one. |
149 | |
150 | =cut |
151 | |
152 | sub next_sibling { |
153 | my( $self ) = @_; |
154 | my $position_column = $self->position_column; |
155 | return ($self->search( |
156 | { $position_column => { '>' => $self->get_column($position_column) } }, |
157 | { rows=>1, order_by => $position_column }, |
158 | )->all())[0]; |
159 | } |
160 | |
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161 | =head2 move_previous |
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162 | |
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163 | $employee->move_previous(); |
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164 | |
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165 | Swaps position with the sibling on position previous in the list. |
166 | 1 is returned on success, and 0 is returned if the objects is already |
167 | the first one. |
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168 | |
169 | =cut |
170 | |
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171 | sub move_previous { |
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172 | my( $self ) = @_; |
173 | my $previous = $self->previous_sibling(); |
174 | return undef if (!$previous); |
175 | my $position_column = $self->position_column; |
176 | my $self_position = $self->get_column( $position_column ); |
177 | $self->set_column( $position_column, $previous->get_column($position_column) ); |
178 | $previous->set_column( $position_column, $self_position ); |
179 | $self->update(); |
180 | $previous->update(); |
181 | return 1; |
182 | } |
183 | |
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184 | =head2 move_next |
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185 | |
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186 | $employee->move_next(); |
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187 | |
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188 | Swaps position with the sibling in the next position. 1 is returned on |
189 | success, and 0 is returned if the object is already the last in the list. |
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190 | |
191 | =cut |
192 | |
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193 | sub move_next { |
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194 | my( $self ) = @_; |
195 | my $next = $self->next_sibling(); |
196 | return undef if (!$next); |
197 | my $position_column = $self->position_column; |
198 | my $self_position = $self->get_column( $position_column ); |
199 | $self->set_column( $position_column, $next->get_column($position_column) ); |
200 | $next->set_column( $position_column, $self_position ); |
201 | $self->update(); |
202 | $next->update(); |
203 | return 1; |
204 | } |
205 | |
206 | =head2 move_first |
207 | |
208 | $employee->move_first(); |
209 | |
210 | Moves the object to the first position. 1 is returned on |
211 | success, and 0 is returned if the object is already the first. |
212 | |
213 | =cut |
214 | |
215 | sub move_first { |
216 | my( $self ) = @_; |
217 | return $self->move_to( 1 ); |
218 | } |
219 | |
220 | =head2 move_last |
221 | |
222 | $employee->move_last(); |
223 | |
224 | Moves the object to the very last position. 1 is returned on |
225 | success, and 0 is returned if the object is already the last one. |
226 | |
227 | =cut |
228 | |
229 | sub move_last { |
230 | my( $self ) = @_; |
231 | my $count = $self->search()->count(); |
232 | return $self->move_to( $count ); |
233 | } |
234 | |
235 | =head2 move_to |
236 | |
237 | $employee->move_to( $position ); |
238 | |
239 | Moves the object to the specified position. 1 is returned on |
240 | success, and 0 is returned if the object is already at the |
241 | specified position. |
242 | |
243 | =cut |
244 | |
245 | sub move_to { |
246 | my( $self, $to_position ) = @_; |
247 | my $position_column = $self->position_column; |
248 | my $from_position = $self->get_column( $position_column ); |
249 | return undef if ( $from_position==$to_position ); |
250 | my $rs = $self->search({ |
251 | -and => [ |
252 | $position_column => { ($from_position>$to_position?'<':'>') => $from_position }, |
253 | $position_column => { ($from_position>$to_position?'>=':'<=') => $to_position }, |
254 | ] |
255 | }); |
256 | my $op = ($from_position>$to_position) ? '+' : '-'; |
257 | $rs->update({ |
258 | $position_column => \"$position_column $op 1", |
259 | }); |
260 | $self->set_column( $position_column => $to_position ); |
261 | $self->update(); |
262 | return 1; |
263 | } |
264 | |
265 | =head2 insert |
266 | |
267 | Overrides the DBIC insert() method by providing a default |
268 | position number. The default will be the number of rows in |
269 | the table +1, thus positioning the new record at the last position. |
270 | |
271 | =cut |
272 | |
273 | sub insert { |
274 | my $self = shift; |
275 | my $position_column = $self->position_column; |
276 | $self->set_column( $position_column => $self->count()+1 ) |
277 | if (!$self->get_column($position_column)); |
278 | $self->next::method( @_ ); |
279 | } |
280 | |
281 | =head2 delete |
282 | |
283 | Overrides the DBIC delete() method by first moving the object |
284 | to the last position, then deleting it, thus ensuring the |
285 | integrity of the positions. |
286 | |
287 | =cut |
288 | |
289 | sub delete { |
290 | my $self = shift; |
291 | $self->move_last; |
292 | $self->next::method( @_ ); |
293 | } |
294 | |
295 | 1; |
296 | __END__ |
297 | |
298 | =head1 TODO |
299 | |
300 | Support foreign keys that cause rows to be members of mini |
301 | positionable sets. |
302 | |
303 | =head1 BUGS |
304 | |
305 | If a position is not specified for an insert than a position |
306 | will be chosen based on COUNT(*)+1. But, it first selects the |
307 | count then inserts the record. The space of time between select |
308 | and insert introduces a race condition. To fix this we need the |
309 | ability to lock tables in DBIC. I've added an entry in the TODO |
310 | about this. |
311 | |
312 | =head1 AUTHOR |
313 | |
314 | Aran Deltac <bluefeet@cpan.org> |
315 | |
316 | =head1 LICENSE |
317 | |
318 | You may distribute this code under the same terms as Perl itself. |
319 | |