relation.rb

# -*- coding: utf-8 -*-
require 'active_support/core_ext/object/blank'
require 'active_support/deprecation'

module ActiveRecord
  # = Active Record Relation
  class Relation
    JoinOperation = Struct.new(:relation, :join_class, :on)

    MULTI_VALUE_METHODS  = [:includes, :eager_load, :preload, :select, :group,
                            :order, :joins, :where, :having, :bind, :references,
                            :extending]

    SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :from, :reordering,
                            :reverse_order, :uniq, :create_with]

    VALUE_METHODS = MULTI_VALUE_METHODS + SINGLE_VALUE_METHODS

    include FinderMethods, Calculations, SpawnMethods, QueryMethods, Batches, Explain, Delegation

    attr_reader :table, :klass, :loaded
    attr_accessor :default_scoped
    alias :loaded? :loaded
    alias :default_scoped? :default_scoped

    def initialize(klass, table, values = {})
      @klass             = klass
      @table             = table
      @values            = values
      @implicit_readonly = nil
      @loaded            = false
      @default_scoped    = false
    end

    def insert(values)
      primary_key_value = nil

      if primary_key && Hash === values
        primary_key_value = values[values.keys.find { |k|
          k.name == primary_key
        }]

        if !primary_key_value && connection.prefetch_primary_key?(klass.table_name)
          primary_key_value = connection.next_sequence_value(klass.sequence_name)
          values[klass.arel_table[klass.primary_key]] = primary_key_value
        end
      end

      im = arel.create_insert
      im.into @table

      conn = @klass.connection

      substitutes = values.sort_by { |arel_attr,_| arel_attr.name }
      binds       = substitutes.map do |arel_attr, value|
        [@klass.columns_hash[arel_attr.name], value]
      end

      substitutes.each_with_index do |tuple, i|
        tuple[1] = conn.substitute_at(binds[i][0], i)
      end

      if values.empty? # empty insert
        im.values = Arel.sql(connection.empty_insert_statement_value)
      else
        im.insert substitutes
      end

      conn.insert(
        im,
        'SQL',
        primary_key,
        primary_key_value,
        nil,
        binds)
    end

    # Initializes new record from relation while maintaining the current
    # scope.
    #
    # Expects arguments in the same format as +Base.new+.
    #
    #   users = User.where(name: 'DHH')
    #   user = users.new # => #<User id: nil, name: "DHH", created_at: nil, updated_at: nil>
    #
    # You can also pass a block to new with the new record as argument:
    #
    #   user = users.new { |user| user.name = 'Oscar' }
    #   user.name # => Oscar
    def new(*args, &block)
      scoping { @klass.new(*args, &block) }
    end

    def initialize_copy(other)
      @values        = @values.dup
      @values[:bind] = @values[:bind].dup if @values[:bind]
      reset
    end

    alias build new

    # Tries to create a new record with the same scoped attributes
    # defined in the relation. Returns the initialized object if validation fails.
    #
    # Expects arguments in the same format as +Base.create+.
    #
    # ==== Examples
    #   users = User.where(name: 'Oscar')
    #   users.create # #<User id: 3, name: "oscar", ...>
    #
    #   users.create(name: 'fxn')
    #   users.create # #<User id: 4, name: "fxn", ...>
    #
    #   users.create { |user| user.name = 'tenderlove' }
    #   # #<User id: 5, name: "tenderlove", ...>
    #
    #   users.create(name: nil) # validation on name
    #   # #<User id: nil, name: nil, ...>
    def create(*args, &block)
      scoping { @klass.create(*args, &block) }
    end

    # Similar to #create, but calls +create!+ on the base class. Raises
    # an exception if a validation error occurs.
    #
    # Expects arguments in the same format as <tt>Base.create!</tt>.
    def create!(*args, &block)
      scoping { @klass.create!(*args, &block) }
    end

    # Tries to load the first record; if it fails, then <tt>create</tt> is called with the same arguments as this method.
    #
    # Expects arguments in the same format as +Base.create+.
    #
    # ==== Examples
    #   # Find the first user named Penélope or create a new one.
    #   User.where(:first_name => 'Penélope').first_or_create
    #   # => <User id: 1, first_name: 'Penélope', last_name: nil>
    #
    #   # Find the first user named Penélope or create a new one.
    #   # We already have one so the existing record will be returned.
    #   User.where(:first_name => 'Penélope').first_or_create
    #   # => <User id: 1, first_name: 'Penélope', last_name: nil>
    #
    #   # Find the first user named Scarlett or create a new one with a particular last name.
    #   User.where(:first_name => 'Scarlett').first_or_create(:last_name => 'Johansson')
    #   # => <User id: 2, first_name: 'Scarlett', last_name: 'Johansson'>
    #
    #   # Find the first user named Scarlett or create a new one with a different last name.
    #   # We already have one so the existing record will be returned.
    #   User.where(:first_name => 'Scarlett').first_or_create do |user|
    #     user.last_name = "O'Hara"
    #   end
    #   # => <User id: 2, first_name: 'Scarlett', last_name: 'Johansson'>
    def first_or_create(attributes = nil, options = {}, &block)
      first || create(attributes, options, &block)
    end

    # Like <tt>first_or_create</tt> but calls <tt>create!</tt> so an exception is raised if the created record is invalid.
    #
    # Expects arguments in the same format as <tt>Base.create!</tt>.
    def first_or_create!(attributes = nil, options = {}, &block)
      first || create!(attributes, options, &block)
    end

    # Like <tt>first_or_create</tt> but calls <tt>new</tt> instead of <tt>create</tt>.
    #
    # Expects arguments in the same format as <tt>Base.new</tt>.
    def first_or_initialize(attributes = nil, options = {}, &block)
      first || new(attributes, options, &block)
    end

    # Runs EXPLAIN on the query or queries triggered by this relation and
    # returns the result as a string. The string is formatted imitating the
    # ones printed by the database shell.
    #
    # Note that this method actually runs the queries, since the results of some
    # are needed by the next ones when eager loading is going on.
    #
    # Please see further details in the
    # {Active Record Query Interface guide}[http://guides.rubyonrails.org/active_record_querying.html#running-explain].
    def explain
      _, queries = collecting_queries_for_explain { exec_queries }
      exec_explain(queries)
    end

    # Converts relation objects to Array.
    def to_a
      # We monitor here the entire execution rather than individual SELECTs
      # because from the point of view of the user fetching the records of a
      # relation is a single unit of work. You want to know if this call takes
      # too long, not if the individual queries take too long.
      #
      # It could be the case that none of the queries involved surpass the
      # threshold, and at the same time the sum of them all does. The user
      # should get a query plan logged in that case.
      logging_query_plan do
        exec_queries
      end
    end

    def exec_queries
      return @records if loaded?

      default_scoped = with_default_scope

      if default_scoped.equal?(self)
        @records = eager_loading? ? find_with_associations : @klass.find_by_sql(arel, bind_values)

        preload = preload_values
        preload +=  includes_values unless eager_loading?
        preload.each do |associations|
          ActiveRecord::Associations::Preloader.new(@records, associations).run
        end

        # @readonly_value is true only if set explicitly. @implicit_readonly is true if there
        # are JOINS and no explicit SELECT.
        readonly = readonly_value.nil? ? @implicit_readonly : readonly_value
        @records.each { |record| record.readonly! } if readonly
      else
        @records = default_scoped.to_a
      end

      @loaded = true
      @records
    end
    private :exec_queries

    def as_json(options = nil) #:nodoc:
      to_a.as_json(options)
    end

    # Returns size of the records.
    def size
      loaded? ? @records.length : count
    end

    # Returns true if there are no records.
    def empty?
      return @records.empty? if loaded?

      c = count
      c.respond_to?(:zero?) ? c.zero? : c.empty?
    end

    # Returns true if there are any records.
    def any?
      if block_given?
        to_a.any? { |*block_args| yield(*block_args) }
      else
        !empty?
      end
    end

    # Returns true if there is more than one record.
    def many?
      if block_given?
        to_a.many? { |*block_args| yield(*block_args) }
      else
        limit_value ? to_a.many? : size > 1
      end
    end

    # Scope all queries to the current scope.
    #
    #   Comment.where(:post_id => 1).scoping do
    #     Comment.first # SELECT * FROM comments WHERE post_id = 1
    #   end
    #
    # Please check unscoped if you want to remove all previous scopes (including
    # the default_scope) during the execution of a block.
    def scoping
      previous, klass.current_scope = klass.current_scope, self
      yield
    ensure
      klass.current_scope = previous
    end

    # Updates all records with details given if they match a set of conditions supplied, limits and order can
    # also be supplied. This method constructs a single SQL UPDATE statement and sends it straight to the
    # database. It does not instantiate the involved models and it does not trigger Active Record callbacks
    # or validations.
    #
    # ==== Parameters
    #
    # * +updates+ - A string, array, or hash representing the SET part of an SQL statement.
    #
    # ==== Examples
    #
    #   # Update all customers with the given attributes
    #   Customer.update_all wants_email: true
    #
    #   # Update all books with 'Rails' in their title
    #   Book.where('title LIKE ?', '%Rails%').update_all(author: 'David')
    #
    #   # Update all books that match conditions, but limit it to 5 ordered by date
    #   Book.where('title LIKE ?', '%Rails%').order(:created_at).limit(5).update_all(:author => 'David')
    def update_all(updates)
      raise ArgumentError, "Empty list of attributes to change" if updates.blank?

      stmt = Arel::UpdateManager.new(arel.engine)

      stmt.set Arel.sql(@klass.send(:sanitize_sql_for_assignment, updates))
      stmt.table(table)
      stmt.key = table[primary_key]

      if joins_values.any?
        @klass.connection.join_to_update(stmt, arel)
      else
        stmt.take(arel.limit)
        stmt.order(*arel.orders)
        stmt.wheres = arel.constraints
      end

      @klass.connection.update stmt, 'SQL', bind_values
    end

    # Updates an object (or multiple objects) and saves it to the database, if validations pass.
    # The resulting object is returned whether the object was saved successfully to the database or not.
    #
    # ==== Parameters
    #
    # * +id+ - This should be the id or an array of ids to be updated.
    # * +attributes+ - This should be a hash of attributes or an array of hashes.
    #
    # ==== Examples
    #
    #   # Updates one record
    #   Person.update(15, user_name: 'Samuel', group: 'expert')
    #
    #   # Updates multiple records
    #   people = { 1 => { "first_name" => "David" }, 2 => { "first_name" => "Jeremy" } }
    #   Person.update(people.keys, people.values)
    def update(id, attributes)
      if id.is_a?(Array)
        id.map.with_index { |one_id, idx| update(one_id, attributes[idx]) }
      else
        object = find(id)
        object.update_attributes(attributes)
        object
      end
    end

    # Destroys the records matching +conditions+ by instantiating each
    # record and calling its +destroy+ method. Each object's callbacks are
    # executed (including <tt>:dependent</tt> association options and
    # +before_destroy+/+after_destroy+ Observer methods). Returns the
    # collection of objects that were destroyed; each will be frozen, to
    # reflect that no changes should be made (since they can't be
    # persisted).
    #
    # Note: Instantiation, callback execution, and deletion of each
    # record can be time consuming when you're removing many records at
    # once. It generates at least one SQL +DELETE+ query per record (or
    # possibly more, to enforce your callbacks). If you want to delete many
    # rows quickly, without concern for their associations or callbacks, use
    # +delete_all+ instead.
    #
    # ==== Parameters
    #
    # * +conditions+ - A string, array, or hash that specifies which records
    #   to destroy. If omitted, all records are destroyed. See the
    #   Conditions section in the introduction to ActiveRecord::Base for
    #   more information.
    #
    # ==== Examples
    #
    #   Person.destroy_all("last_login < '2004-04-04'")
    #   Person.destroy_all(status: "inactive")
    #   Person.where(:age => 0..18).destroy_all
    def destroy_all(conditions = nil)
      if conditions
        where(conditions).destroy_all
      else
        to_a.each {|object| object.destroy }.tap { reset }
      end
    end

    # Destroy an object (or multiple objects) that has the given id. The object is instantiated first,
    # therefore all callbacks and filters are fired off before the object is deleted. This method is
    # less efficient than ActiveRecord#delete but allows cleanup methods and other actions to be run.
    #
    # This essentially finds the object (or multiple objects) with the given id, creates a new object
    # from the attributes, and then calls destroy on it.
    #
    # ==== Parameters
    #
    # * +id+ - Can be either an Integer or an Array of Integers.
    #
    # ==== Examples
    #
    #   # Destroy a single object
    #   Todo.destroy(1)
    #
    #   # Destroy multiple objects
    #   todos = [1,2,3]
    #   Todo.destroy(todos)
    def destroy(id)
      if id.is_a?(Array)
        id.map { |one_id| destroy(one_id) }
      else
        find(id).destroy
      end
    end

    # Deletes the records matching +conditions+ without instantiating the records
    # first, and hence not calling the +destroy+ method nor invoking callbacks. This
    # is a single SQL DELETE statement that goes straight to the database, much more
    # efficient than +destroy_all+. Be careful with relations though, in particular
    # <tt>:dependent</tt> rules defined on associations are not honored. Returns the
    # number of rows affected.
    #
    #   Post.delete_all("person_id = 5 AND (category = 'Something' OR category = 'Else')")
    #   Post.delete_all(["person_id = ? AND (category = ? OR category = ?)", 5, 'Something', 'Else'])
    #   Post.where(:person_id => 5).where(:category => ['Something', 'Else']).delete_all
    #
    # Both calls delete the affected posts all at once with a single DELETE statement.
    # If you need to destroy dependent associations or call your <tt>before_*</tt> or
    # +after_destroy+ callbacks, use the +destroy_all+ method instead.
    #
    # If a limit scope is supplied, +delete_all+ raises an ActiveRecord error:
    #
    #   Post.limit(100).delete_all
    #   # => ActiveRecord::ActiveRecordError: delete_all doesn't support limit scope
    def delete_all(conditions = nil)
      raise ActiveRecordError.new("delete_all doesn't support limit scope") if self.limit_value

      if conditions
        where(conditions).delete_all
      else
        stmt = Arel::DeleteManager.new(arel.engine)
        stmt.from(table)

        if joins_values.any?
          @klass.connection.join_to_delete(stmt, arel, table[primary_key])
        else
          stmt.wheres = arel.constraints
        end

        affected = @klass.connection.delete(stmt, 'SQL', bind_values)

        reset
        affected
      end
    end

    # Deletes the row with a primary key matching the +id+ argument, using a
    # SQL +DELETE+ statement, and returns the number of rows deleted. Active
    # Record objects are not instantiated, so the object's callbacks are not
    # executed, including any <tt>:dependent</tt> association options or
    # Observer methods.
    #
    # You can delete multiple rows at once by passing an Array of <tt>id</tt>s.
    #
    # Note: Although it is often much faster than the alternative,
    # <tt>#destroy</tt>, skipping callbacks might bypass business logic in
    # your application that ensures referential integrity or performs other
    # essential jobs.
    #
    # ==== Examples
    #
    #   # Delete a single row
    #   Todo.delete(1)
    #
    #   # Delete multiple rows
    #   Todo.delete([2,3,4])
    def delete(id_or_array)
      where(primary_key => id_or_array).delete_all
    end

    # Forces reloading of relation.
    def reload
      reset
      to_a # force reload
      self
    end

    def reset
      @first = @last = @to_sql = @order_clause = @scope_for_create = @arel = @loaded = nil
      @should_eager_load = @join_dependency = nil
      @records = []
      self
    end

    # Returns sql statement for the relation.
    #
    #   Users.where(name: 'Oscar').to_sql
    #   # => SELECT "users".* FROM "users"  WHERE "users"."name" = 'Oscar'
    def to_sql
      @to_sql ||= klass.connection.to_sql(arel, bind_values.dup)
    end

    # Returns a hash of where conditions
    #
    #   Users.where(name: 'Oscar').where_values_hash
    #   # => {:name=>"oscar"}
    def where_values_hash
      equalities = with_default_scope.where_values.grep(Arel::Nodes::Equality).find_all { |node|
        node.left.relation.name == table_name
      }

      binds = Hash[bind_values.find_all(&:first).map { |column, v| [column.name, v] }]

      Hash[equalities.map { |where|
        name = where.left.name
        [name, binds.fetch(name.to_s) { where.right }]
      }]
    end

    def scope_for_create
      @scope_for_create ||= where_values_hash.merge(create_with_value)
    end

    # Returns true if relation needs eager loading.
    def eager_loading?
      @should_eager_load ||=
        eager_load_values.any? ||
        includes_values.any? && (joined_includes_values.any? || references_eager_loaded_tables?)
    end

    # Joins that are also marked for preloading. In which case we should just eager load them.
    # Note that this is a naive implementation because we could have strings and symbols which
    # represent the same association, but that aren't matched by this. Also, we could have
    # nested hashes which partially match, e.g. { :a => :b } & { :a => [:b, :c] }
    def joined_includes_values
      includes_values & joins_values
    end

    # Compares two relations for equality.
    def ==(other)
      case other
      when Relation
        other.to_sql == to_sql
      when Array
        to_a == other
      end
    end

    def pretty_print(q)
      q.pp(self.to_a)
    end

    def with_default_scope #:nodoc:
      if default_scoped? && default_scope = klass.send(:build_default_scope)
        default_scope = default_scope.merge(self)
        default_scope.default_scoped = false
        default_scope
      else
        self
      end
    end

    # Returns true if relation is blank.
    def blank?
      to_a.blank?
    end

    def values
      @values.dup
    end

    def inspect
      entries = to_a.take([limit_value, 11].compact.min).map!(&:inspect)
      entries[10] = '...' if entries.size == 11

      "#<#{self.class.name} [#{entries.join(', ')}]>"
    end

    private

    def references_eager_loaded_tables?
      joined_tables = arel.join_sources.map do |join|
        if join.is_a?(Arel::Nodes::StringJoin)
          tables_in_string(join.left)
        else
          [join.left.table_name, join.left.table_alias]
        end
      end

      joined_tables += [table.name, table.table_alias]

      # always convert table names to downcase as in Oracle quoted table names are in uppercase
      joined_tables = joined_tables.flatten.compact.map { |t| t.downcase }.uniq
      string_tables = tables_in_string(to_sql)

      if (references_values - joined_tables).any?
        true
      elsif (string_tables - joined_tables).any?
        ActiveSupport::Deprecation.warn(
          "It looks like you are eager loading table(s) (one of: #{string_tables.join(', ')}) " \
          "that are referenced in a string SQL snippet. For example: \n" \
          "\n" \
          "    Post.includes(:comments).where(\"comments.title = 'foo'\")\n" \
          "\n" \
          "Currently, Active Record recognises the table in the string, and knows to JOIN the " \
          "comments table to the query, rather than loading comments in a separate query. " \
          "However, doing this without writing a full-blown SQL parser is inherently flawed. " \
          "Since we don't want to write an SQL parser, we are removing this functionality. " \
          "From now on, you must explicitly tell Active Record when you are referencing a table " \
          "from a string:\n" \
          "\n" \
          "    Post.includes(:comments).where(\"comments.title = 'foo'\").references(:comments)\n\n"
        )
        true
      else
        false
      end
    end

    def tables_in_string(string)
      return [] if string.blank?
      # always convert table names to downcase as in Oracle quoted table names are in uppercase
      # ignore raw_sql_ that is used by Oracle adapter as alias for limit/offset subqueries
      string.scan(/([a-zA-Z_][.\w]+).?\./).flatten.map{ |s| s.downcase }.uniq - ['raw_sql_']
    end
  end
end