Class: Pageturner

Inherits:
Object
  • Object
show all
Defined in:
lib/pageturner.rb

Defined Under Namespace

Classes: Exception

Constant Summary collapse

ASC = 
"asc"
COMPARATOR_INTERNAL_BUG = 
"sort_direction input has an unexpected value. Contact Pageturner mantainer for support."
DESC = 
"desc"
GREATER_THAN_OPERATOR = 
">"
LESS_THAN_OPERATOR = 
"<"
LOOKAHEAD = 
1

Instance Method Summary collapse

Constructor Details

#initialize(anchor_column:, anchor_value:, ar_relation:, sort_direction:, page_size:, anchor_id:, anchor_column_active_record_identifier: nil, anchor_column_sql_identifier: nil) ⇒ Pageturner

Returns a new instance of Pageturner.

Parameters:

  • anchor_column (String) —

    • Field to paginate on.

  • anchor_value (Anything, nil) —

    • Value of the anchor_column for the record to paginate from.

  • ar_relation (ActiveRecord::Relation) —

    • Resource collection to paginate.

  • sort_direction (String) —

    • Order of the pagination. Valid values: Pageturner::ASC, Pageturner::DESC.

  • anchor_id (Number) —

    • ID of the record to paginate from.

  • anchor_column_active_record_identifier (String, nil) (defaults to: nil) —

    • Method chain that references the anchor column in the model you are paginating.

  • anchor_column_sql_identifier (String, nil) (defaults to: nil) —

    • SQL identifier that references the anchor column in your database schema.



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# File 'lib/pageturner.rb', line 16

def initialize(anchor_column:, anchor_value:, ar_relation:, sort_direction:, page_size:, anchor_id:, anchor_column_active_record_identifier: nil, anchor_column_sql_identifier: nil)
  @anchor_column = anchor_column

  @anchor_column_active_record_identifier = anchor_column_active_record_identifier || @anchor_column
  @anchor_column_sql_identifier = anchor_column_sql_identifier || @anchor_column

  @anchor_value = anchor_value

  @ar_relation = ar_relation

  # Always select id to use it as secondary sort to prevent non-deterministic ordering when primary sort is on a non-unique column.
  unless primary_key_selected?(@ar_relation)
    raise Exception::PrimaryKeyNotSelected, "The provided ActiveRecord::Relation does not have the primary key selected. Cursor pagination requires a primary key to paginate undeterministic columns."
  end

  @sort_direction = sort_direction
  @page_size = page_size
  @anchor_id = anchor_id

  unless [Pageturner::ASC, Pageturner::DESC].include?(@sort_direction)
    raise Exception::InvalidSortDirection, "The provided order is not supported. Supported order values are: '#{ASC}', '#{DESC}'"
  end
end

Instance Method Details

#has_next_page? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/pageturner.rb', line 40

def has_next_page?
  # Load the current page.
  self.resources

  @has_next_page
end

#next_cursor ⇒ Object 



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# File 'lib/pageturner.rb', line 54

def next_cursor
  {
    anchor_column: @anchor_column,
    anchor_id: self.resources.last&.id,
    anchor_value: try_chain(self.resources.last, @anchor_column_active_record_identifier),
    page_size: @page_size,
    sort_direction: @sort_direction
  }
end

#resources ⇒ Object 



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# File 'lib/pageturner.rb', line 47

def resources
  # Memoize expensive querying.
  return @result if defined?(@result)

  @result = calculate_resources
end