Module | Sequel::Plugins::RcteTree |
In: |
lib/sequel/plugins/rcte_tree.rb
|
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.
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.
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
You can override the options for any specific association by making sure the plugin options contain one of the following keys:
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:
Create the appropriate parent, children, ancestors, and descendants associations for the model.
# File lib/sequel/plugins/rcte_tree.rb, line 95 95: def self.apply(model, 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 = SQL::ColumnAll.new(model.table_name) 113: 114: a = opts.merge(opts.fetch(:ancestors, {})) 115: ancestors = a.fetch(:name, :ancestors) 116: a[:read_only] = true unless a.has_key?(:read_only) 117: a[:eager_loader_key] = key 118: a[:dataset] ||= proc do 119: base_ds = model.filter(prkey=>send(key)) 120: recursive_ds = model.join(t, key=>prkey) 121: if c = a[:conditions] 122: (base_ds, recursive_ds) = [base_ds, recursive_ds].collect do |ds| 123: (c.is_a?(Array) && !Sequel.condition_specifier?(c)) ? ds.filter(*c) : ds.filter(c) 124: end 125: end 126: table_alias = model.dataset.schema_and_table(model.table_name)[1].to_sym 127: model.from(t => table_alias). 128: with_recursive(t, base_ds.select_all, 129: recursive_ds. 130: select(c_all)) 131: end 132: aal = Array(a[:after_load]) 133: aal << proc do |m, ancs| 134: unless m.associations.has_key?(parent) 135: parent_map = {m[prkey]=>m} 136: child_map = {} 137: child_map[m[key]] = m if m[key] 138: m.associations[parent] = nil 139: ancs.each do |obj| 140: obj.associations[parent] = nil 141: parent_map[obj[prkey]] = obj 142: if ok = obj[key] 143: child_map[ok] = obj 144: end 145: end 146: parent_map.each do |parent_id, obj| 147: if child = child_map[parent_id] 148: child.associations[parent] = obj 149: end 150: end 151: end 152: end 153: a[:after_load] ||= aal 154: a[:eager_loader] ||= proc do |eo| 155: id_map = eo[:key_hash][key] 156: parent_map = {} 157: children_map = {} 158: eo[:rows].each do |obj| 159: parent_map[obj[prkey]] = obj 160: (children_map[obj[key]] ||= []) << obj 161: obj.associations[ancestors] = [] 162: obj.associations[parent] = nil 163: end 164: r = model.association_reflection(ancestors) 165: base_case = model.filter(prkey=>id_map.keys). 166: select(SQL::AliasedExpression.new(prkey, ka), c_all) 167: recursive_case = model.join(t, key=>prkey). 168: select(SQL::QualifiedIdentifier.new(t, ka), c_all) 169: if c = r[:conditions] 170: (base_case, recursive_case) = [base_case, recursive_case].collect do |ds| 171: (c.is_a?(Array) && !Sequel.condition_specifier?(c)) ? ds.filter(*c) : ds.filter(c) 172: end 173: end 174: table_alias = model.dataset.schema_and_table(model.table_name)[1].to_sym 175: elds = model.eager_loading_dataset(r, 176: model.from(t => table_alias). 177: with_recursive(t, base_case, 178: recursive_case), 179: r.select, 180: eo[:associations], eo) 181: elds = elds.select_append(ka) unless elds.opts[:select] == nil 182: elds.all do |obj| 183: opk = obj[prkey] 184: if in_pm = parent_map.has_key?(opk) 185: if idm_obj = parent_map[opk] 186: idm_obj.values[ka] = obj.values[ka] 187: obj = idm_obj 188: end 189: else 190: obj.associations[parent] = nil 191: parent_map[opk] = obj 192: (children_map[obj[key]] ||= []) << obj 193: end 194: 195: if roots = id_map[obj.values.delete(ka)] 196: roots.each do |root| 197: root.associations[ancestors] << obj 198: end 199: end 200: end 201: parent_map.each do |parent_id, obj| 202: if children = children_map[parent_id] 203: children.each do |child| 204: child.associations[parent] = obj 205: end 206: end 207: end 208: end 209: model.one_to_many ancestors, a 210: 211: d = opts.merge(opts.fetch(:descendants, {})) 212: descendants = d.fetch(:name, :descendants) 213: d[:read_only] = true unless d.has_key?(:read_only) 214: la = d[:level_alias] ||= :x_level_x 215: d[:dataset] ||= proc do 216: base_ds = model.filter(key=>send(prkey)) 217: recursive_ds = model.join(t, prkey=>key) 218: if c = d[:conditions] 219: (base_ds, recursive_ds) = [base_ds, recursive_ds].collect do |ds| 220: (c.is_a?(Array) && !Sequel.condition_specifier?(c)) ? ds.filter(*c) : ds.filter(c) 221: end 222: end 223: table_alias = model.dataset.schema_and_table(model.table_name)[1].to_sym 224: model.from(t => table_alias). 225: with_recursive(t, base_ds.select_all, 226: recursive_ds. 227: select(SQL::ColumnAll.new(model.table_name))) 228: end 229: dal = Array(d[:after_load]) 230: dal << proc do |m, descs| 231: unless m.associations.has_key?(childrena) 232: parent_map = {m[prkey]=>m} 233: children_map = {} 234: m.associations[childrena] = [] 235: descs.each do |obj| 236: obj.associations[childrena] = [] 237: if opk = obj[prkey] 238: parent_map[opk] = obj 239: end 240: if ok = obj[key] 241: (children_map[ok] ||= []) << obj 242: end 243: end 244: children_map.each do |parent_id, objs| 245: parent_map[parent_id].associations[childrena] = objs 246: end 247: end 248: end 249: d[:after_load] = dal 250: d[:eager_loader] ||= proc do |eo| 251: id_map = eo[:key_hash][prkey] 252: associations = eo[:associations] 253: parent_map = {} 254: children_map = {} 255: eo[:rows].each do |obj| 256: parent_map[obj[prkey]] = obj 257: obj.associations[descendants] = [] 258: obj.associations[childrena] = [] 259: end 260: r = model.association_reflection(descendants) 261: base_case = model.filter(key=>id_map.keys). 262: select(SQL::AliasedExpression.new(key, ka), c_all) 263: recursive_case = model.join(t, prkey=>key). 264: select(SQL::QualifiedIdentifier.new(t, ka), c_all) 265: if c = r[:conditions] 266: (base_case, recursive_case) = [base_case, recursive_case].collect do |ds| 267: (c.is_a?(Array) && !Sequel.condition_specifier?(c)) ? ds.filter(*c) : ds.filter(c) 268: end 269: end 270: if associations.is_a?(Integer) 271: level = associations 272: no_cache_level = level - 1 273: associations = {} 274: base_case = base_case.select_more(SQL::AliasedExpression.new(0, la)) 275: recursive_case = recursive_case.select_more(SQL::AliasedExpression.new(SQL::QualifiedIdentifier.new(t, la) + 1, la)).filter(SQL::QualifiedIdentifier.new(t, la) < level - 1) 276: end 277: table_alias = model.dataset.schema_and_table(model.table_name)[1].to_sym 278: elds = model.eager_loading_dataset(r, 279: model.from(t => table_alias).with_recursive(t, base_case, recursive_case), 280: r.select, 281: associations, eo) 282: elds = elds.select_append(ka) unless elds.opts[:select] == nil 283: elds.all do |obj| 284: if level 285: no_cache = no_cache_level == obj.values.delete(la) 286: end 287: 288: opk = obj[prkey] 289: if in_pm = parent_map.has_key?(opk) 290: if idm_obj = parent_map[opk] 291: idm_obj.values[ka] = obj.values[ka] 292: obj = idm_obj 293: end 294: else 295: obj.associations[childrena] = [] unless no_cache 296: parent_map[opk] = obj 297: end 298: 299: if root = id_map[obj.values.delete(ka)].first 300: root.associations[descendants] << obj 301: end 302: 303: (children_map[obj[key]] ||= []) << obj 304: end 305: children_map.each do |parent_id, objs| 306: parent_map[parent_id].associations[childrena] = objs.uniq 307: end 308: end 309: model.one_to_many descendants, d 310: end