Module Sequel::Plugins::RcteTree
In: lib/sequel/plugins/rcte_tree.rb

Overview

The rcte_tree plugin deals with tree structured data stored in the database using the adjacency list model (where child rows have a foreign key pointing to the parent rows), using recursive common table expressions to load all ancestors in a single query, all descendants in a single query, and all descendants to a given level (where level 1 is children, level 2 is children and grandchildren etc.) in a single query.

Background

There are two types of common models for storing tree structured data in an SQL database, the adjacency list model and the nested set model. Before recursive common table expressions (or similar capabilities such as CONNECT BY for Oracle), the nested set model was the only easy way to retrieve all ancestors and descendants in a single query. However, it has significant performance corner cases.

On PostgreSQL 8.4, with a significant number of rows, the nested set model is almost 500 times slower than using a recursive common table expression with the adjacency list model to get all descendants, and almost 24,000 times slower to get all descendants to a given level.

Considering that the nested set model requires more difficult management than the adjacency list model, it‘s almost always better to use the adjacency list model if your database supports common table expressions. See explainextended.com/2009/09/24/adjacency-list-vs-nested-sets-postgresql/ for detailed analysis.

Usage

The rcte_tree plugin adds four associations to the model: parent, children, ancestors, and descendants. Both the parent and children are fairly standard many_to_one and one_to_many associations, respectively. However, the ancestors and descendants associations are special. Both the ancestors and descendants associations will automatically set the parent and children associations, respectively, for current object and all of the ancestor or descendant objects, whenever they are loaded (either eagerly or lazily). Additionally, the descendants association can take a level argument when called eagerly, which limits the returned objects to only that many levels in the tree (see the Overview).

  Model.plugin :rcte_tree

  # Lazy loading
  model = Model.first
  model.parent
  model.children
  model.ancestors # Populates :parent association for all ancestors
  model.descendants # Populates :children association for all descendants

  # Eager loading - also populates the :parent and children associations
  # for all ancestors and descendants
  Model.filter(:id=>[1, 2]).eager(:ancestors, :descendants).all

  # Eager loading children and grand children
  Model.filter(:id=>[1, 2]).eager(:descendants=>2).all
  # Eager loading children, grand children, and great grand children
  Model.filter(:id=>[1, 2]).eager(:descendants=>3).all

Options

You can override the options for any specific association by making sure the plugin options contain one of the following keys:

:parent :hash of options for the parent association
:children :hash of options for the children association
:ancestors :hash of options for the ancestors association
:descendants :hash of options for the descendants association

Note that you can change the name of the above associations by specifying a :name key in the appropriate hash of options above. For example:

  Model.plugin :rcte_tree, :parent=>{:name=>:mother},
   :children=>{:name=>:daughters}, :descendants=>{:name=>:offspring}

Any other keys in the main options hash are treated as options shared by all of the associations. Here‘s a few options that affect the plugin:

:key :The foreign key in the table that points to the primary key of the parent (default: :parent_id)
:primary_key :The primary key to use (default: the model‘s primary key)
:key_alias :The symbol identifier to use for aliasing when eager loading (default: :x_root_x)
:cte_name :The symbol identifier to use for the common table expression (default: :t)
:level_alias :The symbol identifier to use when eagerly loading descendants up to a given level (default: :x_level_x)

Methods

apply  

Public Class methods

Create the appropriate parent, children, ancestors, and descendants associations for the model.

[Source]

     # File lib/sequel/plugins/rcte_tree.rb, line 95
 95:       def self.apply(model, opts=OPTS)
 96:         model.plugin :tree, opts
 97: 
 98:         opts = opts.dup
 99:         opts[:class] = model
100:         opts[:methods_module] = Module.new
101:         model.send(:include, opts[:methods_module])
102:         
103:         key = opts[:key] ||= :parent_id
104:         prkey = opts[:primary_key] ||= model.primary_key
105:         ka = opts[:key_alias] ||= :x_root_x
106:         t = opts[:cte_name] ||= :t
107:         c_all = if model.dataset.recursive_cte_requires_column_aliases?
108:           # Work around Oracle/ruby-oci8 bug that returns integers as BigDecimals in recursive queries.
109:           conv_bd = model.db.database_type == :oracle
110:           col_aliases = model.dataset.columns
111:           model_table = model.table_name
112:           col_aliases.map{|c| SQL::QualifiedIdentifier.new(model_table, c)}
113:         else
114:           [SQL::ColumnAll.new(model.table_name)]
115:         end
116:         
117:         bd_conv = lambda{|v| conv_bd && v.is_a?(BigDecimal) ? v.to_i : v}
118: 
119:         key_array = Array(key)
120:         prkey_array = Array(prkey)
121:         if key.is_a?(Array)
122:           key_conv = lambda{|m| key_array.map{|k| m[k]}}
123:           key_present = lambda{|m| key_conv[m].all?}
124:           prkey_conv = lambda{|m| prkey_array.map{|k| m[k]}}
125:           key_aliases = (0...key_array.length).map{|i| "#{ka}_#{i}""#{ka}_#{i}"}
126:           ka_conv = lambda{|m| key_aliases.map{|k| m[k]}}
127:           ancestor_base_case_columns = prkey_array.zip(key_aliases).map{|k, ka_| SQL::AliasedExpression.new(k, ka_)} + c_all
128:           descendant_base_case_columns = key_array.zip(key_aliases).map{|k, ka_| SQL::AliasedExpression.new(k, ka_)} + c_all
129:           recursive_case_columns = prkey_array.zip(key_aliases).map{|k, ka_| SQL::QualifiedIdentifier.new(t, ka_)} + c_all
130:           extract_key_alias = lambda{|m| key_aliases.map{|ka_| bd_conv[m.values.delete(ka_)]}}
131:         else
132:           key_present = key_conv = lambda{|m| m[key]}
133:           prkey_conv = lambda{|m| m[prkey]}
134:           key_aliases = [ka]
135:           ka_conv = lambda{|m| m[ka]}
136:           ancestor_base_case_columns = [SQL::AliasedExpression.new(prkey, ka)] + c_all
137:           descendant_base_case_columns = [SQL::AliasedExpression.new(key, ka)] + c_all
138:           recursive_case_columns = [SQL::QualifiedIdentifier.new(t, ka)] + c_all
139:           extract_key_alias = lambda{|m| bd_conv[m.values.delete(ka)]}
140:         end
141:         
142:         parent = opts.merge(opts.fetch(:parent, {})).fetch(:name, :parent)
143:         childrena = opts.merge(opts.fetch(:children, {})).fetch(:name, :children)
144:         
145:         opts[:reciprocal] = nil
146:         a = opts.merge(opts.fetch(:ancestors, {}))
147:         ancestors = a.fetch(:name, :ancestors)
148:         a[:read_only] = true unless a.has_key?(:read_only)
149:         a[:eager_loader_key] = key
150:         a[:dataset] ||= proc do
151:           base_ds = model.filter(prkey_array.zip(key_array.map{|k| get_column_value(k)}))
152:           recursive_ds = model.join(t, key_array.zip(prkey_array))
153:           if c = a[:conditions]
154:             (base_ds, recursive_ds) = [base_ds, recursive_ds].collect do |ds|
155:               (c.is_a?(Array) && !Sequel.condition_specifier?(c)) ? ds.filter(*c) : ds.filter(c)
156:             end
157:           end
158:           table_alias = model.dataset.schema_and_table(model.table_name)[1].to_sym
159:           model.from(SQL::AliasedExpression.new(t, table_alias)).
160:            with_recursive(t, col_aliases ? base_ds.select(*col_aliases) : base_ds.select_all,
161:             recursive_ds.select(*c_all),
162:             :args=>col_aliases)
163:         end
164:         aal = Array(a[:after_load])
165:         aal << proc do |m, ancs|
166:           unless m.associations.has_key?(parent)
167:             parent_map = {prkey_conv[m]=>m}
168:             child_map = {}
169:             child_map[key_conv[m]] = m if key_present[m]
170:             m.associations[parent] = nil
171:             ancs.each do |obj|
172:               obj.associations[parent] = nil
173:               parent_map[prkey_conv[obj]] = obj
174:               if ok = key_conv[obj]
175:                 child_map[ok] = obj
176:               end
177:             end
178:             parent_map.each do |parent_id, obj|
179:               if child = child_map[parent_id]
180:                 child.associations[parent] = obj
181:               end
182:             end
183:           end
184:         end
185:         a[:after_load] ||= aal
186:         a[:eager_loader] ||= proc do |eo|
187:           id_map = eo[:id_map]
188:           parent_map = {}
189:           children_map = {}
190:           eo[:rows].each do |obj|
191:             parent_map[prkey_conv[obj]] = obj
192:             (children_map[key_conv[obj]] ||= []) << obj
193:             obj.associations[ancestors] = []
194:             obj.associations[parent] = nil
195:           end
196:           r = model.association_reflection(ancestors)
197:           base_case = model.filter(prkey=>id_map.keys).
198:            select(*ancestor_base_case_columns)
199:           recursive_case = model.join(t, key_array.zip(prkey_array)).
200:            select(*recursive_case_columns)
201:           if c = r[:conditions]
202:             (base_case, recursive_case) = [base_case, recursive_case].collect do |ds|
203:               (c.is_a?(Array) && !Sequel.condition_specifier?(c)) ? ds.filter(*c) : ds.filter(c)
204:             end
205:           end
206:           table_alias = model.dataset.schema_and_table(model.table_name)[1].to_sym
207:           ds = model.from(SQL::AliasedExpression.new(t, table_alias)).
208:             with_recursive(t, base_case, recursive_case,
209:              :args=>((key_aliases + col_aliases) if col_aliases))
210:           ds = r.apply_eager_dataset_changes(ds)
211:           ds = ds.select_append(ka) unless ds.opts[:select] == nil
212:           model.eager_load_results(r, eo.merge(:loader=>false, :initalize_rows=>false, :dataset=>ds, :id_map=>nil)) do |obj|
213:             opk = prkey_conv[obj]
214:             if parent_map.has_key?(opk)
215:               if idm_obj = parent_map[opk]
216:                 key_aliases.each{|ka_| idm_obj.values[ka_] = obj.values[ka_]}
217:                 obj = idm_obj
218:               end
219:             else
220:               obj.associations[parent] = nil
221:               parent_map[opk] = obj
222:               (children_map[key_conv[obj]] ||= []) << obj
223:             end
224:             
225:             if roots = id_map[extract_key_alias[obj]]
226:               roots.each do |root|
227:                 root.associations[ancestors] << obj
228:               end
229:             end
230:           end
231:           parent_map.each do |parent_id, obj|
232:             if children = children_map[parent_id]
233:               children.each do |child|
234:                 child.associations[parent] = obj
235:               end
236:             end
237:           end
238:         end
239:         model.one_to_many ancestors, a
240:         
241:         d = opts.merge(opts.fetch(:descendants, {}))
242:         descendants = d.fetch(:name, :descendants)
243:         d[:read_only] = true unless d.has_key?(:read_only)
244:         la = d[:level_alias] ||= :x_level_x
245:         d[:dataset] ||= proc do
246:           base_ds = model.filter(key_array.zip(prkey_array.map{|k| get_column_value(k)}))
247:           recursive_ds = model.join(t, prkey_array.zip(key_array))
248:           if c = d[:conditions]
249:             (base_ds, recursive_ds) = [base_ds, recursive_ds].collect do |ds|
250:               (c.is_a?(Array) && !Sequel.condition_specifier?(c)) ? ds.filter(*c) : ds.filter(c)
251:             end
252:           end
253:           table_alias = model.dataset.schema_and_table(model.table_name)[1].to_sym
254:           model.from(SQL::AliasedExpression.new(t, table_alias)).
255:            with_recursive(t, col_aliases ? base_ds.select(*col_aliases) : base_ds.select_all,
256:             recursive_ds.select(*c_all),
257:             :args=>col_aliases)
258:           end
259:         dal = Array(d[:after_load])
260:         dal << proc do |m, descs|
261:           unless m.associations.has_key?(childrena)
262:             parent_map = {prkey_conv[m]=>m}
263:             children_map = {}
264:             m.associations[childrena] = []
265:             descs.each do |obj|
266:               obj.associations[childrena] = []
267:               if opk = prkey_conv[obj]
268:                 parent_map[opk] = obj
269:               end
270:               if ok = key_conv[obj]
271:                 (children_map[ok] ||= []) << obj
272:               end
273:             end
274:             children_map.each do |parent_id, objs|
275:               parent_obj = parent_map[parent_id]
276:               parent_obj.associations[childrena] = objs
277:               objs.each do |obj|
278:                 obj.associations[parent] = parent_obj
279:               end
280:             end
281:           end
282:         end
283:         d[:after_load] = dal
284:         d[:eager_loader] ||= proc do |eo|
285:           id_map = eo[:id_map]
286:           associations = eo[:associations]
287:           parent_map = {}
288:           children_map = {}
289:           eo[:rows].each do |obj|
290:             parent_map[prkey_conv[obj]] = obj
291:             obj.associations[descendants] = []
292:             obj.associations[childrena] = []
293:           end
294:           r = model.association_reflection(descendants)
295:           base_case = model.filter(key=>id_map.keys).
296:            select(*descendant_base_case_columns)
297:           recursive_case = model.join(t, prkey_array.zip(key_array)).
298:            select(*recursive_case_columns)
299:           if c = r[:conditions]
300:             (base_case, recursive_case) = [base_case, recursive_case].collect do |ds|
301:               (c.is_a?(Array) && !Sequel.condition_specifier?(c)) ? ds.filter(*c) : ds.filter(c)
302:             end
303:           end
304:           if associations.is_a?(Integer)
305:             level = associations
306:             no_cache_level = level - 1
307:             associations = {}
308:             base_case = base_case.select_more(SQL::AliasedExpression.new(Sequel.cast(0, Integer), la))
309:             recursive_case = recursive_case.select_more(SQL::AliasedExpression.new(SQL::QualifiedIdentifier.new(t, la) + 1, la)).filter(SQL::QualifiedIdentifier.new(t, la) < level - 1)
310:           end
311:           table_alias = model.dataset.schema_and_table(model.table_name)[1].to_sym
312:           ds = model.from(SQL::AliasedExpression.new(t, table_alias)).
313:             with_recursive(t, base_case, recursive_case,
314:               :args=>((key_aliases + col_aliases + (level ? [la] : [])) if col_aliases))
315:           ds = r.apply_eager_dataset_changes(ds)
316:           ds = ds.select_append(ka) unless ds.opts[:select] == nil
317:           model.eager_load_results(r, eo.merge(:loader=>false, :initalize_rows=>false, :dataset=>ds, :id_map=>nil, :associations=>{})) do |obj|
318:             if level
319:               no_cache = no_cache_level == obj.values.delete(la)
320:             end
321:             
322:             opk = prkey_conv[obj]
323:             if parent_map.has_key?(opk)
324:               if idm_obj = parent_map[opk]
325:                 key_aliases.each{|ka_| idm_obj.values[ka_] = obj.values[ka_]}
326:                 obj = idm_obj
327:               end
328:             else
329:               obj.associations[childrena] = [] unless no_cache
330:               parent_map[opk] = obj
331:             end
332:             
333:             if root = id_map[extract_key_alias[obj]].first
334:               root.associations[descendants] << obj
335:             end
336:             
337:             (children_map[key_conv[obj]] ||= []) << obj
338:           end
339:           children_map.each do |parent_id, objs|
340:             objs = objs.uniq
341:             parent_obj = parent_map[parent_id]
342:             parent_obj.associations[childrena] = objs
343:             objs.each do |obj|
344:               obj.associations[parent] = parent_obj
345:             end
346:           end
347:         end
348:         model.one_to_many descendants, d
349:       end

[Validate]