230 lines
12 KiB
Ruby
230 lines
12 KiB
Ruby
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module ActiveRecord
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module Calculations #:nodoc:
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CALCULATIONS_OPTIONS = [:conditions, :joins, :order, :select, :group, :having, :distinct, :limit, :offset]
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def self.included(base)
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base.extend(ClassMethods)
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end
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module ClassMethods
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# Count operates using three different approaches.
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#
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# * Count all: By not passing any parameters to count, it will return a count of all the rows for the model.
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# * Count by conditions or joins: For backwards compatibility, you can pass in +conditions+ and +joins+ as individual parameters.
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# * Count using options will find the row count matched by the options used.
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#
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# The last approach, count using options, accepts an option hash as the only parameter. The options are:
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#
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# * <tt>:conditions</tt>: An SQL fragment like "administrator = 1" or [ "user_name = ?", username ]. See conditions in the intro.
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# * <tt>:joins</tt>: An SQL fragment for additional joins like "LEFT JOIN comments ON comments.post_id = id". (Rarely needed).
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# The records will be returned read-only since they will have attributes that do not correspond to the table's columns.
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# * <tt>:include</tt>: Named associations that should be loaded alongside using LEFT OUTER JOINs. The symbols named refer
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# to already defined associations. When using named associations count returns the number DISTINCT items for the model you're counting.
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# See eager loading under Associations.
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# * <tt>:order</tt>: An SQL fragment like "created_at DESC, name" (really only used with GROUP BY calculations).
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# * <tt>:group</tt>: An attribute name by which the result should be grouped. Uses the GROUP BY SQL-clause.
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# * <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
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# include the joined columns.
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# * <tt>:distinct</tt>: Set this to true to make this a distinct calculation, such as SELECT COUNT(DISTINCT posts.id) ...
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#
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# Examples for counting all:
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# Person.count # returns the total count of all people
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#
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# Examples for count by +conditions+ and +joins+ (for backwards compatibility):
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# Person.count("age > 26") # returns the number of people older than 26
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# Person.find("age > 26 AND job.salary > 60000", "LEFT JOIN jobs on jobs.person_id = person.id") # returns the total number of rows matching the conditions and joins fetched by SELECT COUNT(*).
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#
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# Examples for count with options:
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# Person.count(:conditions => "age > 26")
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# 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.
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# 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.
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# Person.count('id', :conditions => "age > 26") # Performs a COUNT(id)
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# Person.count(:all, :conditions => "age > 26") # Performs a COUNT(*) (:all is an alias for '*')
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#
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# Note: Person.count(:all) will not work because it will use :all as the condition. Use Person.count instead.
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def count(*args)
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options = {}
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column_name = :all
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# For backwards compatibility, we need to handle both count(conditions=nil, joins=nil) or count(options={}) or count(column_name=:all, options={}).
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if args.size >= 0 && args.size <= 2
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if args.first.is_a?(Hash)
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options = args.first
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elsif args[1].is_a?(Hash)
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options = args[1]
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column_name = args.first
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else
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# Handle legacy paramter options: def count(conditions=nil, joins=nil)
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options.merge!(:conditions => args[0]) if args.length > 0
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options.merge!(:joins => args[1]) if args.length > 1
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end
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else
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raise(ArgumentError, "Unexpected parameters passed to count(*args): expected either count(conditions=nil, joins=nil) or count(options={})")
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end
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if options[:include] || scope(:find, :include)
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count_with_associations(options)
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else
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calculate(:count, column_name, options)
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end
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end
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# Calculates average value on a given column. The value is returned as a float. See #calculate for examples with options.
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#
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# Person.average('age')
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def average(column_name, options = {})
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calculate(:avg, column_name, options)
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end
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# Calculates the minimum value on a given column. The value is returned with the same data type of the column.. See #calculate for examples with options.
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#
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# Person.minimum('age')
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def minimum(column_name, options = {})
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calculate(:min, column_name, options)
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end
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# Calculates the maximum value on a given column. The value is returned with the same data type of the column.. See #calculate for examples with options.
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#
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# Person.maximum('age')
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def maximum(column_name, options = {})
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calculate(:max, column_name, options)
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end
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# Calculates the sum value on a given column. The value is returned with the same data type of the column.. See #calculate for examples with options.
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#
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# Person.sum('age')
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def sum(column_name, options = {})
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calculate(:sum, column_name, options)
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end
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# This calculates aggregate values in the given column: Methods for count, sum, average, minimum, and maximum have been added as shortcuts.
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# Options such as :conditions, :order, :group, :having, and :joins can be passed to customize the query.
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#
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# There are two basic forms of output:
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# * 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.
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# * Grouped values: This returns an ordered hash of the values and groups them by the :group option. It takes either a column name, or the name
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# of a belongs_to association.
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#
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# values = Person.maximum(:age, :group => 'last_name')
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# puts values["Drake"]
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# => 43
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#
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# drake = Family.find_by_last_name('Drake')
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# values = Person.maximum(:age, :group => :family) # Person belongs_to :family
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# puts values[drake]
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# => 43
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#
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# values.each do |family, max_age|
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# ...
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# end
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#
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# Options:
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# * <tt>:conditions</tt>: An SQL fragment like "administrator = 1" or [ "user_name = ?", username ]. See conditions in the intro.
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# * <tt>:joins</tt>: An SQL fragment for additional joins like "LEFT JOIN comments ON comments.post_id = id". (Rarely needed).
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# The records will be returned read-only since they will have attributes that do not correspond to the table's columns.
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# * <tt>:order</tt>: An SQL fragment like "created_at DESC, name" (really only used with GROUP BY calculations).
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# * <tt>:group</tt>: An attribute name by which the result should be grouped. Uses the GROUP BY SQL-clause.
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# * <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
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# include the joined columns.
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# * <tt>:distinct</tt>: Set this to true to make this a distinct calculation, such as SELECT COUNT(DISTINCT posts.id) ...
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#
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# Examples:
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# Person.calculate(:count, :all) # The same as Person.count
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# Person.average(:age) # SELECT AVG(age) FROM people...
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# Person.minimum(:age, :conditions => ['last_name != ?', 'Drake']) # Selects the minimum age for everyone with a last name other than 'Drake'
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# Person.minimum(:age, :having => 'min(age) > 17', :group => :last_name) # Selects the minimum age for any family without any minors
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def calculate(operation, column_name, options = {})
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validate_calculation_options(operation, options)
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column_name = options[:select] if options[:select]
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column_name = '*' if column_name == :all
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column = column_for column_name
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aggregate = select_aggregate(operation, column_name, options)
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aggregate_alias = column_alias_for(operation, column_name)
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if options[:group]
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execute_grouped_calculation(operation, column_name, column, aggregate, aggregate_alias, options)
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else
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execute_simple_calculation(operation, column_name, column, aggregate, aggregate_alias, options)
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end
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end
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protected
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def construct_calculation_sql(aggregate, aggregate_alias, options) #:nodoc:
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scope = scope(:find)
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sql = "SELECT #{aggregate} AS #{aggregate_alias}"
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sql << ", #{options[:group_field]} AS #{options[:group_alias]}" if options[:group]
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sql << " FROM #{table_name} "
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add_joins!(sql, options, scope)
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add_conditions!(sql, options[:conditions], scope)
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sql << " GROUP BY #{options[:group_field]}" if options[:group]
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sql << " HAVING #{options[:having]}" if options[:group] && options[:having]
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sql << " ORDER BY #{options[:order]}" if options[:order]
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add_limit!(sql, options)
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sql
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end
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def execute_simple_calculation(operation, column_name, column, aggregate, aggregate_alias, options) #:nodoc:
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value = connection.select_value(construct_calculation_sql(aggregate, aggregate_alias, options))
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type_cast_calculated_value(value, column, operation)
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end
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def execute_grouped_calculation(operation, column_name, column, aggregate, aggregate_alias, options) #:nodoc:
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group_attr = options[:group].to_s
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association = reflect_on_association(group_attr.to_sym)
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associated = association && association.macro == :belongs_to # only count belongs_to associations
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group_field = (associated ? "#{options[:group]}_id" : options[:group]).to_s
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group_alias = column_alias_for(group_field)
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group_column = column_for group_field
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sql = construct_calculation_sql(aggregate, aggregate_alias, options.merge(:group_field => group_field, :group_alias => group_alias))
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calculated_data = connection.select_all(sql)
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if association
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key_ids = calculated_data.collect { |row| row[group_alias] }
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key_records = association.klass.base_class.find(key_ids)
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key_records = key_records.inject({}) { |hsh, r| hsh.merge(r.id => r) }
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end
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calculated_data.inject(OrderedHash.new) do |all, row|
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key = associated ? key_records[row[group_alias].to_i] : type_cast_calculated_value(row[group_alias], group_column)
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value = row[aggregate_alias]
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all << [key, type_cast_calculated_value(value, column, operation)]
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end
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end
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private
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def validate_calculation_options(operation, options = {})
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if operation.to_s == 'count'
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options.assert_valid_keys(CALCULATIONS_OPTIONS + [:include])
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else
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options.assert_valid_keys(CALCULATIONS_OPTIONS)
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end
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end
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def select_aggregate(operation, column_name, options)
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"#{operation}(#{'DISTINCT ' if options[:distinct]}#{column_name})"
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end
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# converts a given key to the value that the database adapter returns as
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#
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# users.id #=> users_id
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# sum(id) #=> sum_id
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# count(distinct users.id) #=> count_distinct_users_id
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# count(*) #=> count_all
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def column_alias_for(*keys)
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keys.join(' ').downcase.gsub(/\*/, 'all').gsub(/\W+/, ' ').strip.gsub(/ +/, '_')
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end
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def column_for(field)
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field_name = field.to_s.split('.').last
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columns.detect { |c| c.name.to_s == field_name }
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end
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def type_cast_calculated_value(value, column, operation = nil)
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operation = operation.to_s.downcase
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case operation
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when 'count' then value.to_i
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when 'avg' then value.to_f
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else column ? column.type_cast(value) : value
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end
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end
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end
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end
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end
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