aboutsummaryrefslogtreecommitdiffstats
path: root/activerecord/lib/active_record/relation/calculations.rb
blob: f613014f2361a77f7cc532d8244e91cf9baf4c34 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
require 'active_support/core_ext/object/blank'
require 'active_support/core_ext/object/try'

module ActiveRecord
  module Calculations
    # Count operates using three different approaches.
    #
    # * Count all: By not passing any parameters to count, it will return a count of all the rows for the model.
    # * Count using column: By passing a column name to count, it will return a count of all the
    #   rows for the model with supplied column present.
    # * Count using options will find the row count matched by the options used.
    #
    # The third approach, count using options, accepts an option hash as the only parameter. The options are:
    #
    # * <tt>:conditions</tt>: An SQL fragment like "administrator = 1" or [ "user_name = ?", username ].
    #   See conditions in the intro to ActiveRecord::Base.
    # * <tt>:joins</tt>: Either an SQL fragment for additional joins like "LEFT JOIN comments ON comments.post_id = id"
    #   (rarely needed) or named associations in the same form used for the <tt>:include</tt> option, which will
    #   perform an INNER JOIN on the associated table(s). If the value is a string, then the records
    #   will be returned read-only since they will have attributes that do not correspond to the table's columns.
    #   Pass <tt>:readonly => false</tt> to override.
    # * <tt>:include</tt>: Named associations that should be loaded alongside using LEFT OUTER JOINs.
    #   The symbols named refer to already defined associations. When using named associations, count
    #   returns the number of DISTINCT items for the model you're counting.
    #   See eager loading under Associations.
    # * <tt>:order</tt>: An SQL fragment like "created_at DESC, name" (really only used with GROUP BY calculations).
    # * <tt>:group</tt>: An attribute name by which the result should be grouped. Uses the GROUP BY SQL-clause.
    # * <tt>:select</tt>: By default, this is * as in SELECT * FROM, but can be changed if you, for example,
    #   want to do a join but not include the joined columns.
    # * <tt>:distinct</tt>: Set this to true to make this a distinct calculation, such as
    #   SELECT COUNT(DISTINCT posts.id) ...
    # * <tt>:from</tt> - By default, this is the table name of the class, but can be changed to an
    #   alternate table name (or even the name of a database view).
    #
    # Examples for counting all:
    #   Person.count         # returns the total count of all people
    #
    # Examples for counting by column:
    #   Person.count(:age)  # returns the total count of all people whose age is present in database
    #
    # Examples for count with options:
    #   Person.count(:conditions => "age > 26")
    #
    #   # because of the named association, it finds the DISTINCT count using LEFT OUTER JOIN.
    #   Person.count(:conditions => "age > 26 AND job.salary > 60000", :include => :job)
    #
    #   # finds the number of rows matching the conditions and joins.
    #   Person.count(:conditions => "age > 26 AND job.salary > 60000",
    #                :joins => "LEFT JOIN jobs on jobs.person_id = person.id")
    #
    #   Person.count('id', :conditions => "age > 26") # Performs a COUNT(id)
    #   Person.count(:all, :conditions => "age > 26") # Performs a COUNT(*) (:all is an alias for '*')
    #
    # Note: <tt>Person.count(:all)</tt> will not work because it will use <tt>:all</tt> as the condition.
    # Use Person.count instead.
    def count(column_name = nil, options = {})
      column_name, options = nil, column_name if column_name.is_a?(Hash)
      calculate(:count, column_name, options)
    end

    # Calculates the average value on a given column. Returns +nil+ if there's
    # no row. See +calculate+ for examples with options.
    #
    #   Person.average('age') # => 35.8
    def average(column_name, options = {})
      calculate(:average, column_name, options)
    end

    # Calculates the minimum value on a given column. The value is returned
    # with the same data type of the column, or +nil+ if there's no row. See
    # +calculate+ for examples with options.
    #
    #   Person.minimum('age') # => 7
    def minimum(column_name, options = {})
      calculate(:minimum, column_name, options)
    end

    # Calculates the maximum value on a given column. The value is returned
    # with the same data type of the column, or +nil+ if there's no row. See
    # +calculate+ for examples with options.
    #
    #   Person.maximum('age') # => 93
    def maximum(column_name, options = {})
      calculate(:maximum, column_name, options)
    end

    # Calculates the sum of values on a given column. The value is returned
    # with the same data type of the column, 0 if there's no row. See
    # +calculate+ for examples with options.
    #
    #   Person.sum('age') # => 4562
    def sum(*args)
      if block_given?
        self.to_a.sum(*args) {|*block_args| yield(*block_args)}
      else
        calculate(:sum, *args)
      end
    end

    # This calculates aggregate values in the given column. Methods for count, sum, average,
    # minimum, and maximum have been added as shortcuts. Options such as <tt>:conditions</tt>,
    # <tt>:order</tt>, <tt>:group</tt>, <tt>:having</tt>, and <tt>:joins</tt> can be passed to customize the query.
    #
    # There are two basic forms of output:
    #   * Single aggregate value: The single value is type cast to Fixnum for COUNT, Float
    #     for AVG, and the given column's type for everything else.
    #   * Grouped values: This returns an ordered hash of the values and groups them by the
    #     <tt>:group</tt> option. It takes either a column name, or the name of a belongs_to association.
    #
    #       values = Person.maximum(:age, :group => 'last_name')
    #       puts values["Drake"]
    #       => 43
    #
    #       drake  = Family.find_by_last_name('Drake')
    #       values = Person.maximum(:age, :group => :family) # Person belongs_to :family
    #       puts values[drake]
    #       => 43
    #
    #       values.each do |family, max_age|
    #       ...
    #       end
    #
    # Options:
    # * <tt>:conditions</tt> - An SQL fragment like "administrator = 1" or [ "user_name = ?", username ].
    #   See conditions in the intro to ActiveRecord::Base.
    # * <tt>:include</tt>: Eager loading, see Associations for details. Since calculations don't load anything,
    #   the purpose of this is to access fields on joined tables in your conditions, order, or group clauses.
    # * <tt>:joins</tt> - An SQL fragment for additional joins like "LEFT JOIN comments ON comments.post_id = id".
    #   (Rarely needed).
    #   The records will be returned read-only since they will have attributes that do not correspond to the
    #   table's columns.
    # * <tt>:order</tt> - An SQL fragment like "created_at DESC, name" (really only used with GROUP BY calculations).
    # * <tt>:group</tt> - An attribute name by which the result should be grouped. Uses the GROUP BY SQL-clause.
    # * <tt>:select</tt> - By default, this is * as in SELECT * FROM, but can be changed if you for example
    #   want to do a join, but not include the joined columns.
    # * <tt>:distinct</tt> - Set this to true to make this a distinct calculation, such as
    #   SELECT COUNT(DISTINCT posts.id) ...
    #
    # Examples:
    #   Person.calculate(:count, :all) # The same as Person.count
    #   Person.average(:age) # SELECT AVG(age) FROM people...
    #   Person.minimum(:age, :conditions => ['last_name != ?', 'Drake']) # Selects the minimum age for
    #                                                                    # everyone with a last name other than 'Drake'
    #
    #   # Selects the minimum age for any family without any minors
    #   Person.minimum(:age, :having => 'min(age) > 17', :group => :last_name)
    #
    #   Person.sum("2 * age")
    def calculate(operation, column_name, options = {})
      if options.except(:distinct).present?
        apply_finder_options(options.except(:distinct)).calculate(operation, column_name, :distinct => options[:distinct])
      else
        relation = with_default_scope

        if relation.equal?(self)
          if eager_loading? || (includes_values.present? && references_eager_loaded_tables?)
            construct_relation_for_association_calculations.calculate(operation, column_name, options)
          else
            perform_calculation(operation, column_name, options)
          end
        else
          relation.calculate(operation, column_name, options)
        end
      end
    rescue ThrowResult
      0
    end

    # This method is designed to perform select by a single column as direct SQL query
    # Returns <tt>Array</tt> with values of the specified column name
    # The values has same data type as column.
    #
    # Examples:
    #
    #   Person.pluck(:id) # SELECT people.id FROM people
    #   Person.uniq.pluck(:role) # SELECT DISTINCT role FROM people
    #   Person.where(:age => 21).limit(5).pluck(:id) # SELECT people.id FROM people WHERE people.age = 21 LIMIT 5
    #
    def pluck(column_name)
      key = column_name.to_s.split('.', 2).last

      if column_name.is_a?(Symbol) && column_names.include?(column_name.to_s)
        column_name = "#{table_name}.#{column_name}"
      end

      result = klass.connection.select_all(select(column_name).arel, nil, bind_values)
      types  = result.column_types.merge klass.column_types
      column = types[key]

      result.map do |attributes|
        value = klass.initialize_attributes(attributes)[key]
        if column
          column.type_cast value
        else
          value
        end
      end
    end

    private

    def perform_calculation(operation, column_name, options = {})
      operation = operation.to_s.downcase

      distinct = options[:distinct]

      if operation == "count"
        column_name ||= (select_for_count || :all)

        unless arel.ast.grep(Arel::Nodes::OuterJoin).empty?
          distinct = true
        end

        column_name = primary_key if column_name == :all && distinct

        distinct = nil if column_name =~ /\s*DISTINCT\s+/i
      end

      if @group_values.any?
        execute_grouped_calculation(operation, column_name, distinct)
      else
        execute_simple_calculation(operation, column_name, distinct)
      end
    end

    def aggregate_column(column_name)
      if @klass.column_names.include?(column_name.to_s)
        Arel::Attribute.new(@klass.unscoped.table, column_name)
      else
        Arel.sql(column_name == :all ? "*" : column_name.to_s)
      end
    end

    def operation_over_aggregate_column(column, operation, distinct)
      operation == 'count' ? column.count(distinct) : column.send(operation)
    end

    def execute_simple_calculation(operation, column_name, distinct) #:nodoc:
      # Postgresql doesn't like ORDER BY when there are no GROUP BY
      relation = reorder(nil)

      if operation == "count" && (relation.limit_value || relation.offset_value)
        # Shortcut when limit is zero.
        return 0 if relation.limit_value == 0

        query_builder = build_count_subquery(relation, column_name, distinct)
      else
        column = aggregate_column(column_name)

        select_value = operation_over_aggregate_column(column, operation, distinct)

        relation.select_values = [select_value]

        query_builder = relation.arel
      end

      result = @klass.connection.select_value(query_builder, nil, relation.bind_values)
      type_cast_calculated_value(result, column_for(column_name), operation)
    end

    def execute_grouped_calculation(operation, column_name, distinct) #:nodoc:
      group_attr      = @group_values
      association     = @klass.reflect_on_association(group_attr.first.to_sym)
      associated      = group_attr.size == 1 && association && association.macro == :belongs_to # only count belongs_to associations
      group_fields  = Array(associated ? association.foreign_key : group_attr)
      group_aliases = group_fields.map { |field| column_alias_for(field) }
      group_columns = group_aliases.zip(group_fields).map { |aliaz,field|
        [aliaz, column_for(field)]
      }

      group = @klass.connection.adapter_name == 'FrontBase' ? group_aliases : group_fields

      if operation == 'count' && column_name == :all
        aggregate_alias = 'count_all'
      else
        aggregate_alias = column_alias_for(operation, column_name)
      end

      select_values = [
        operation_over_aggregate_column(
          aggregate_column(column_name),
          operation,
          distinct).as(aggregate_alias)
      ]
      select_values += @select_values unless @having_values.empty?

      select_values.concat group_fields.zip(group_aliases).map { |field,aliaz|
        "#{field} AS #{aliaz}"
      }

      relation = except(:group).group(group.join(','))
      relation.select_values = select_values

      calculated_data = @klass.connection.select_all(relation, nil, bind_values)

      if association
        key_ids     = calculated_data.collect { |row| row[group_aliases.first] }
        key_records = association.klass.base_class.find(key_ids)
        key_records = Hash[key_records.map { |r| [r.id, r] }]
      end

      Hash[calculated_data.map do |row|
        key   = group_columns.map { |aliaz, column|
          type_cast_calculated_value(row[aliaz], column)
        }
        key   = key.first if key.size == 1
        key = key_records[key] if associated
        [key, type_cast_calculated_value(row[aggregate_alias], column_for(column_name), operation)]
      end]
    end

    # Converts the given keys to the value that the database adapter returns as
    # a usable column name:
    #
    #   column_alias_for("users.id")                 # => "users_id"
    #   column_alias_for("sum(id)")                  # => "sum_id"
    #   column_alias_for("count(distinct users.id)") # => "count_distinct_users_id"
    #   column_alias_for("count(*)")                 # => "count_all"
    #   column_alias_for("count", "id")              # => "count_id"
    def column_alias_for(*keys)
      table_name = keys.join(' ')
      table_name.downcase!
      table_name.gsub!(/\*/, 'all')
      table_name.gsub!(/\W+/, ' ')
      table_name.strip!
      table_name.gsub!(/ +/, '_')

      @klass.connection.table_alias_for(table_name)
    end

    def column_for(field)
      field_name = field.to_s.split('.').last
      @klass.columns.detect { |c| c.name.to_s == field_name }
    end

    def type_cast_calculated_value(value, column, operation = nil)
      case operation
        when 'count'   then value.to_i
        when 'sum'     then type_cast_using_column(value || '0', column)
        when 'average' then value.respond_to?(:to_d) ? value.to_d : value
        else type_cast_using_column(value, column)
      end
    end

    def type_cast_using_column(value, column)
      column ? column.type_cast(value) : value
    end

    def select_for_count
      if @select_values.present?
        select = @select_values.join(", ")
        select if select !~ /[,*]/
      end
    end

    def build_count_subquery(relation, column_name, distinct)
      column_alias = Arel.sql('count_column')
      subquery_alias = Arel.sql('subquery_for_count')

      aliased_column = aggregate_column(column_name == :all ? 1 : column_name).as(column_alias)
      relation.select_values = [aliased_column]
      subquery = relation.arel.as(subquery_alias)

      sm = Arel::SelectManager.new relation.engine
      select_value = operation_over_aggregate_column(column_alias, 'count', distinct)
      sm.project(select_value).from(subquery)
    end
  end
end