Class: GraphQL::Pagination::Connection

Inherits:
Object
  • Object
show all
Defined in:
lib/graphql/pagination/connection.rb

Overview

A Connection wraps a list of items and provides cursor-based pagination over it.

Connections were introduced by Facebook's Relay front-end framework, but proved to be generally useful for GraphQL APIs. When in doubt, use connections to serve lists (like Arrays, ActiveRecord::Relations) via GraphQL.

Unlike the previous connection implementation, these default to bidirectional pagination.

Pagination arguments and context may be provided at initialization or assigned later (see Schema::Field::ConnectionExtension).

Direct Known Subclasses

ArrayConnection, RelationConnection

Defined Under Namespace

Classes: Edge, PaginationImplementationMissingError

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(items, parent: nil, field: nil, context: nil, first: nil, after: nil, max_page_size: :not_given, last: nil, before: nil, edge_class: nil, arguments: nil) ⇒ Connection

Returns a new instance of Connection.

Parameters:

  • items (Object)

    some unpaginated collection item, like an Array or ActiveRecord::Relation

  • context (Query::Context) (defaults to: nil)
  • parent (Object) (defaults to: nil)

    The object this collection belongs to

  • first (Integer, nil) (defaults to: nil)

    The limit parameter from the client, if it provided one

  • after (String, nil) (defaults to: nil)

    A cursor for pagination, if the client provided one

  • last (Integer, nil) (defaults to: nil)

    Limit parameter from the client, if provided

  • before (String, nil) (defaults to: nil)

    A cursor for pagination, if the client provided one.

  • arguments (Hash) (defaults to: nil)

    The arguments to the field that returned the collection wrapped by this connection

  • max_page_size (Integer, nil) (defaults to: :not_given)

    A configured value to cap the result size. Applied as first if neither first or last are given.


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# File 'lib/graphql/pagination/connection.rb', line 60

def initialize(items, parent: nil, field: nil, context: nil, first: nil, after: nil, max_page_size: :not_given, last: nil, before: nil, edge_class: nil, arguments: nil)
  @items = items
  @parent = parent
  @context = context
  @field = field
  @first_value = first
  @after_value = after
  @last_value = last
  @before_value = before
  @arguments = arguments
  @edge_class = edge_class || self.class::Edge
  # This is only true if the object was _initialized_ with an override
  # or if one is assigned later.
  @has_max_page_size_override = max_page_size != :not_given
  @max_page_size = if max_page_size == :not_given
    nil
  else
    max_page_size
  end
end

Instance Attribute Details

#after_valueObject

Raw access to client-provided values. (max_page_size not applied to first or last.)


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# File 'lib/graphql/pagination/connection.rb', line 28

def after_value
  @after_value
end

#argumentsHash<Symbol => Object>

Returns The field arguments from the field that returned this connection.

Returns:

  • (Hash<Symbol => Object>)

    The field arguments from the field that returned this connection


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# File 'lib/graphql/pagination/connection.rb', line 49

def arguments
  @arguments
end

#before_valueObject

Raw access to client-provided values. (max_page_size not applied to first or last.)


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# File 'lib/graphql/pagination/connection.rb', line 28

def before_value
  @before_value
end

#contextGraphQL::Query::Context


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# File 'lib/graphql/pagination/connection.rb', line 22

def context
  @context
end

#edge_classClass

Returns A wrapper class for edges of this connection.

Returns:

  • (Class)

    A wrapper class for edges of this connection


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# File 'lib/graphql/pagination/connection.rb', line 134

def edge_class
  @edge_class
end

#fieldGraphQL::Schema::Field

Returns The field this connection was returned by.

Returns:


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# File 'lib/graphql/pagination/connection.rb', line 137

def field
  @field
end

#firstInteger?

Returns A clamped first value. (The underlying instance variable doesn't have limits on it.) If neither first nor last is given, but max_page_size is present, max_page_size is used for first.

Returns:

  • (Integer, nil)

    A clamped first value. (The underlying instance variable doesn't have limits on it.) If neither first nor last is given, but max_page_size is present, max_page_size is used for first.


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# File 'lib/graphql/pagination/connection.rb', line 103

def first
  @first ||= begin
    capped = limit_pagination_argument(@first_value, max_page_size)
    if capped.nil? && last.nil?
      capped = max_page_size
    end
    capped
  end
end

#first_valueObject

Raw access to client-provided values. (max_page_size not applied to first or last.)


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# File 'lib/graphql/pagination/connection.rb', line 28

def first_value
  @first_value
end

#itemsObject (readonly)

Returns A list object, from the application. This is the unpaginated value passed into the connection.

Returns:

  • (Object)

    A list object, from the application. This is the unpaginated value passed into the connection.


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# File 'lib/graphql/pagination/connection.rb', line 19

def items
  @items
end

#lastInteger?

Returns A clamped last value. (The underlying instance variable doesn't have limits on it).

Returns:

  • (Integer, nil)

    A clamped last value. (The underlying instance variable doesn't have limits on it)


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# File 'lib/graphql/pagination/connection.rb', line 124

def last
  @last ||= limit_pagination_argument(@last_value, max_page_size)
end

#last_valueObject

Raw access to client-provided values. (max_page_size not applied to first or last.)


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# File 'lib/graphql/pagination/connection.rb', line 28

def last_value
  @last_value
end

#parentObject

Returns the object this collection belongs to.

Returns:

  • (Object)

    the object this collection belongs to


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# File 'lib/graphql/pagination/connection.rb', line 25

def parent
  @parent
end

Instance Method Details

#afterString?

Returns the client-provided cursor. "" is treated as nil.

Returns:

  • (String, nil)

    the client-provided cursor. "" is treated as nil.


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# File 'lib/graphql/pagination/connection.rb', line 40

def after
  if defined?(@after)
    @after
  else
    @after = @after_value == "" ? nil : @after_value
  end
end

#beforeString?

Returns the client-provided cursor. "" is treated as nil.

Returns:

  • (String, nil)

    the client-provided cursor. "" is treated as nil.


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# File 'lib/graphql/pagination/connection.rb', line 31

def before
  if defined?(@before)
    @before
  else
    @before = @before_value == "" ? nil : @before_value
  end
end

#cursor_for(item) ⇒ String

Return a cursor for this item.

Parameters:

  • item (Object)

    one of the passed in #items, taken from #nodes

Returns:

  • (String)

Raises:


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# File 'lib/graphql/pagination/connection.rb', line 178

def cursor_for(item)
  raise PaginationImplementationMissingError, "Implement #{self.class}#cursor_for(item) to return the cursor for #{item.inspect}"
end

#edge_nodesObject

Deprecated.

use #nodes instead

A dynamic alias for compatibility with Relay::BaseConnection.


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# File 'lib/graphql/pagination/connection.rb', line 146

def edge_nodes
  nodes
end

#edgesArray<Edge>

Returns #nodes, but wrapped with Edge instances.

Returns:

  • (Array<Edge>)

    #nodes, but wrapped with Edge instances


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# File 'lib/graphql/pagination/connection.rb', line 129

def edges
  @edges ||= nodes.map { |n| @edge_class.new(n, self) }
end

#end_cursorString

Returns The cursor of the last item in #nodes.

Returns:

  • (String)

    The cursor of the last item in #nodes


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# File 'lib/graphql/pagination/connection.rb', line 171

def end_cursor
  nodes.last && cursor_for(nodes.last)
end

#has_max_page_size_override?Boolean

Returns:

  • (Boolean)

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# File 'lib/graphql/pagination/connection.rb', line 94

def has_max_page_size_override?
  @has_max_page_size_override
end

#has_next_pageBoolean

Returns True if there are more items after this page.

Returns:

  • (Boolean)

    True if there are more items after this page

Raises:


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# File 'lib/graphql/pagination/connection.rb', line 156

def has_next_page
  raise PaginationImplementationMissingError, "Implement #{self.class}#has_next_page to return the next-page check"
end

#has_previous_pageBoolean

Returns True if there were items before these items.

Returns:

  • (Boolean)

    True if there were items before these items

Raises:


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# File 'lib/graphql/pagination/connection.rb', line 161

def has_previous_page
  raise PaginationImplementationMissingError, "Implement #{self.class}#has_previous_page to return the previous-page check"
end

#max_page_sizeObject


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# File 'lib/graphql/pagination/connection.rb', line 86

def max_page_size
  if @has_max_page_size_override
    @max_page_size
  else
    context.schema.default_max_page_size
  end
end

#max_page_size=(new_value) ⇒ Object


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# File 'lib/graphql/pagination/connection.rb', line 81

def max_page_size=(new_value)
  @has_max_page_size_override = true
  @max_page_size = new_value
end

#nodesArray<Object>

Returns A slice of #items, constrained by @first_value/@after_value/@last_value/@before_value.

Returns:

  • (Array<Object>)

    A slice of #items, constrained by @first_value/@after_value/@last_value/@before_value

Raises:


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# File 'lib/graphql/pagination/connection.rb', line 140

def nodes
  raise PaginationImplementationMissingError, "Implement #{self.class}#nodes to paginate `@items`"
end

#page_infoObject

The connection object itself implements PageInfo fields


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# File 'lib/graphql/pagination/connection.rb', line 151

def page_info
  self
end

#range_add_edge(item) ⇒ Edge

This is called by Relay::RangeAdd -- it can be overridden when item needs some modifications based on this connection's state.

Parameters:

  • item (Object)

    An item newly added to items

Returns:


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# File 'lib/graphql/pagination/connection.rb', line 118

def range_add_edge(item)
  edge_class.new(item, self)
end

#start_cursorString

Returns The cursor of the first item in #nodes.

Returns:

  • (String)

    The cursor of the first item in #nodes


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# File 'lib/graphql/pagination/connection.rb', line 166

def start_cursor
  nodes.first && cursor_for(nodes.first)
end