Class: HQ::GraphQL::PaginatedAssociationLoader

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

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(model, association_name, internal_association: false, limit: nil, offset: nil, scope: 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 19

def initialize(model, association_name, internal_association: false, limit: nil, offset: nil, scope: nil, sort_by: nil, sort_order: nil)
  super()
  @model                = model
  @association_name     = association_name
  @internal_association = internal_association
  @limit                = [0, limit].max if limit
  @offset               = [0, offset].max if offset
  @scope                = scope
  @sort_by              = sort_by || :created_at
  @sort_order           = normalize_sort_order(sort_order)

  validate!
end

Class Method Details

.for(*args, scope: nil, **kwargs) ⇒ Object 



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# File 'lib/hq/graphql/paginated_association_loader.rb', line 8

def self.for(*args, scope: nil, **kwargs)
  if scope
    raise TypeError, "scope must be an ActiveRecord::Relation" unless scope.is_a?(::ActiveRecord::Relation)
    executor = ::GraphQL::Batch::Executor.current
    loader_key = loader_key_for(*args, **kwargs, scope: scope.to_sql)
    executor.loader(loader_key) { new(*args, **kwargs, scope: scope) }
  else
    super
  end
end

Instance Method Details

#cache_key(record) ⇒ Object 



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# File 'lib/hq/graphql/paginated_association_loader.rb', line 38

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 33

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 42

def perform(records)
  values = records.map { |r| source_value(r) }
  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
      lateral_join_table = through_reflection? ? through_association.klass.arel_table : inner_table
      from_table         = lateral_join_table.alias("outer")

      inside_scope = default_scope.
        select(inner_table[::Arel.star]).
        where(lateral_join_table[target_join_key].eq(from_table[target_join_key])).
        reorder(arel_order(inner_table)).
        limit(@limit).
        offset(@offset)

      if through_reflection?
        # expose the through_reflection key
        inside_scope = inside_scope.select(lateral_join_table[target_join_key])
      end

      lateral_table = ::Arel::Table.new("top")
      association_class.
        select(lateral_table[::Arel.star]).distinct.
        from(from_table).
        where(from_table[target_join_key].in(values)).
        joins("INNER JOIN LATERAL (#{inside_scope.to_sql}) #{lateral_table.name} ON TRUE").
        reorder(arel_order(lateral_table))
    else
      scope = default_scope.reorder(arel_order(association_class.arel_table))

      if through_reflection?
        scope.where(through_association.name => { target_join_key => values }).
          # expose the through_reflection key
          select(association_class.arel_table[::Arel.star], through_association.klass.arel_table[target_join_key])
      else
        scope.where(target_join_key => values)
      end
    end

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