Class: HQ::GraphQL::PaginatedAssociationLoader

Inherits:
GraphQL::Batch::Loader
  • Object
show all
Defined in:
lib/hq/graphql/paginated_association_loader.rb

Instance Method Summary collapse

Constructor Details

#initialize(model, association_name, limit: nil, offset: nil, sort_by: nil, sort_order: nil) ⇒ PaginatedAssociationLoader

Returns a new instance of PaginatedAssociationLoader.



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# File 'lib/hq/graphql/paginated_association_loader.rb', line 6

def initialize(model, association_name, limit: nil, offset: nil, sort_by: nil, sort_order: nil)
  @model            = model
  @association_name = association_name
  @limit            = [0, limit].max if limit
  @offset           = [0, offset].max if offset
  @sort_by          = sort_by || :updated_at
  @sort_order       = normalize_sort_order(sort_order)

  validate!
end

Instance Method Details

#cache_key(record) ⇒ Object 



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# File 'lib/hq/graphql/paginated_association_loader.rb', line 22

def cache_key(record)
  record.send(primary_key)
end

#load(record) ⇒ Object

Raises:

  • (TypeError) 


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# File 'lib/hq/graphql/paginated_association_loader.rb', line 17

def load(record)
  raise TypeError, "#{@model} loader can't load association for #{record.class}" unless record.is_a?(@model)
  super
end

#perform(records) ⇒ Object 



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# File 'lib/hq/graphql/paginated_association_loader.rb', line 26

def perform(records)
  scope =
    if @limit || @offset
      # If a limit or offset is added, then we need to transform the query
      # into a lateral join so that we can limit on groups of data.
      #
      # > SELECT * FROM addresses WHERE addresses.user_id IN ($1, $2, ..., $N) ORDER BY addresses.created_at DESC;
      # ...becomes
      # > SELECT DISTINCT a_top.*
      # > FROM addresses
      # > INNER JOIN LATERAL (
      # >   SELECT inner.*
      # >   FROM addresses inner
      # >   WHERE inner.user_id = addresses.user_id
      # >   ORDER BY inner.created_at DESC
      # >   LIMIT 1
      # > ) a_top ON TRUE
      # > WHERE addresses.user_id IN ($1, $2, ..., $N)
      # > ORDER BY a_top.created_at DESC
      inner_table       = association_class.arel_table
      association_table = inner_table.alias("outer")

      inside_scope = default_scope.
        select(inner_table[::Arel.star]).
        from(inner_table).
        where(inner_table[association_key].eq(association_table[association_key])).
        reorder(arel_order(inner_table)).
        limit(@limit).
        offset(@offset)

      outside_table = ::Arel::Table.new("top")
      association_class.
        select(outside_table[::Arel.star]).distinct.
        from(association_table).
        joins("INNER JOIN LATERAL (#{inside_scope.to_sql}) #{outside_table.name} ON TRUE").
        where(association_table[association_key].in(records.map { |r| join_value(r) })).
        reorder(arel_order(outside_table))
    else
      default_scope.
        reorder(arel_order(association_class.arel_table)).
        where(association_key => records.map { |r| join_value(r) })
    end

  results = scope.to_a
  records.each do |record|
    fulfill(record, association_value(record, results)) unless fulfilled?(record)
  end
end