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Diffstat (limited to 'activerecord/lib/active_record/relation/calculations.rb')
| -rw-r--r-- | activerecord/lib/active_record/relation/calculations.rb | 259 |
1 files changed, 259 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb new file mode 100644 index 0000000000..e77424a64b --- /dev/null +++ b/activerecord/lib/active_record/relation/calculations.rb @@ -0,0 +1,259 @@ +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") + # Person.count(:conditions => "age > 26 AND job.salary > 60000", :include => :job) # because of the named association, it finds the DISTINCT count using LEFT OUTER JOIN. + # Person.count(:conditions => "age > 26 AND job.salary > 60000", :joins => "LEFT JOIN jobs on jobs.person_id = person.id") # finds the number of rows matching the conditions and joins. + # 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. The value is returned as + # a float, or +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(column_name, options = {}) + calculate(:sum, column_name, options) + 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' + # Person.minimum(:age, :having => 'min(age) > 17', :group => :last_name) # Selects the minimum age for any family without any minors + # 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 + if eager_loading? || includes_values.present? + construct_relation_for_association_calculations.calculate(operation, column_name, options) + else + perform_calculation(operation, column_name, options) + end + end + rescue ThrowResult + 0 + end + + private + + def perform_calculation(operation, column_name, options = {}) + operation = operation.to_s.downcase + + if operation == "count" + column_name ||= (select_for_count || :all) + + joins = arel.joins(arel) + if joins.present? && joins =~ /LEFT OUTER/i + distinct = true + column_name = @klass.primary_key if column_name == :all + end + + distinct = nil if column_name.to_s =~ /\s*DISTINCT\s+/i + distinct ||= options[:distinct] + else + distinct = nil + end + + distinct = options[:distinct] || distinct + column_name = :all if column_name.blank? && operation == "count" + + if @group_values.any? + return execute_grouped_calculation(operation, column_name) + else + return execute_simple_calculation(operation, column_name, distinct) + end + end + + def execute_simple_calculation(operation, column_name, distinct) #:nodoc: + column = if @klass.column_names.include?(column_name.to_s) + Arel::Attribute.new(@klass.unscoped, column_name) + else + Arel::SqlLiteral.new(column_name == :all ? "*" : column_name.to_s) + end + + # Postgresql doesn't like ORDER BY when there are no GROUP BY + relation = except(:order).select(operation == 'count' ? column.count(distinct) : column.send(operation)) + type_cast_calculated_value(@klass.connection.select_value(relation.to_sql), column_for(column_name), operation) + end + + def execute_grouped_calculation(operation, column_name) #:nodoc: + group_attr = @group_values.first + association = @klass.reflect_on_association(group_attr.to_sym) + associated = association && association.macro == :belongs_to # only count belongs_to associations + group_field = associated ? association.primary_key_name : group_attr + group_alias = column_alias_for(group_field) + group_column = column_for(group_field) + + group = @klass.connection.adapter_name == 'FrontBase' ? group_alias : group_field + + aggregate_alias = column_alias_for(operation, column_name) + + select_statement = if operation == 'count' && column_name == :all + "COUNT(*) AS count_all" + else + Arel::Attribute.new(@klass.unscoped, column_name).send(operation).as(aggregate_alias).to_sql + end + + select_statement << ", #{group_field} AS #{group_alias}" + + relation = select(select_statement).group(group) + + calculated_data = @klass.connection.select_all(relation.to_sql) + + if association + key_ids = calculated_data.collect { |row| row[group_alias] } + key_records = association.klass.base_class.find(key_ids) + key_records = key_records.inject({}) { |hsh, r| hsh.merge(r.id => r) } + end + + calculated_data.inject(ActiveSupport::OrderedHash.new) do |all, row| + key = type_cast_calculated_value(row[group_alias], group_column) + key = key_records[key] if associated + value = row[aggregate_alias] + all[key] = type_cast_calculated_value(value, column_for(column_name), operation) + all + 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 && (value.is_a?(Fixnum) ? value.to_f : value).to_d + 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 + end +end |