count

• Class methods (1)
• included (
• Instance methods (35)
• aggregate_column
• all_attributes?(>= v6.1.3.1)
• async_average (>= v7.1.3.2)
• async_count (>= v7.1.3.2)
• async_ids (>= v7.1.3.2)
• async_maximum (>= v7.1.3.2)
• async_minimum (>= v7.1.3.2)
• async_pick (>= v7.1.3.2)
• async_pluck (>= v7.1.3.2)
• async_sum (>= v7.1.3.2)
• average
• build_count_subquery
• calculate
• column_alias_for
• column_for(
• count
• distinct_select?
• execute_grouped_calculation
• execute_simple_calculation
• has_include?
• ids
• lookup_cast_type_from_join_.(>= v6.1.3.1)
• maximum
• minimum
• operation_over_aggregate_co.
• perform_calculation
• pick (>= v6.0.0)
• pluck
• select_for_count
• sum
• type_cast (
• type_cast_calculated_value
• type_cast_pluck_values(>= v6.1.3.1)
• type_cast_using_column(
• type_for

= private
= protected

Count the records.

Person.count # => the total count of all people Person.count(:age) # => returns the total count of all people whose age is present in database Person.count(:all) # => performs a COUNT(*) (:all is an alias for '*') Person.distinct.count(:age) # => counts the number of different age values 

If #count is used with [rdoc-ref:QueryMethods#group], it returns a Hash whose keys represent the aggregated column, and the values are the respective amounts:

Person.group(:city).count # => < 'Rome' =>5, 'Paris' => 3 > 

If #count is used with [rdoc-ref:QueryMethods#group] for multiple columns, it returns a Hash whose keys are an array containing the individual values of each column and the value of each key would be the #count.

Article.group(:status, :category).count # => <["draft", "business"]=>10, ["draft", "technology"]=>4, ["published", "business"]=>0, ["published", "technology"]=>2> 

Person.select(:age).count # => counts the number of different age values 

Note: not all valid [rdoc-ref:QueryMethods#select] expressions are valid #count expressions. The specifics differ between databases. In invalid cases, an error from the database is thrown.

# File activerecord/lib/active_record/relation/calculations.rb, line 41 def count(column_name = nil) if block_given? unless column_name.nil? ActiveSupport::Deprecation.warn "When `count' is called with a block, it ignores other arguments. " "This behavior is now deprecated and will result in an ArgumentError in Rails 6.0." end return super() end calculate(:count, column_name) end

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