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

[Validate]