Module: Mongoid::Slug::Index

Defined in:
lib/mongoid/slug/index.rb

Class Method Summary collapse

Class Method Details

.build_index(scope_key = nil, by_model_type = false) ⇒ Array(Hash, Hash)

Returns the indexable fields and index options.

Parameters:

  • scope_key (String or Symbol) (defaults to: nil) —

    The optional scope key for the index

  • by_model_type (Boolean) (defaults to: false) —

    Whether or not

Returns:

  • (Array(Hash, Hash)) —

    the indexable fields and index options.



8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
 
# File 'lib/mongoid/slug/index.rb', line 8

def self.build_index(scope_key = nil, by_model_type = false)
  # The order of field keys is intentional.
  # See: http://docs.mongodb.org/manual/core/index-compound/
  fields = {}
  fields[:_type] = 1       if by_model_type
  fields[scope_key] = 1 if scope_key
  fields[:_slugs] = 1

  # By design, we use the unique index constraint when possible to enforce slug uniqueness.
  # When migrating legacy data to Mongoid slug, the _slugs field may be null on many records,
  # hence we set the sparse index option to ignore these from the unique index.
  # See: http://docs.mongodb.org/manual/core/index-sparse/
  #
  # There are three edge cases where the index must not be unique:
  #
  # 1) Legacy tables with `scope_key`. The sparse indexes on compound keys (scope + _slugs) are
  #    whenever ANY of the key values are present (e.g. when scope is set and _slugs is unset),
  #    and collisions will occur when multiple records have the same scope but null slugs.
  #
  # 2) Single Table Inheritance (`by_model_type`). MongoDB creates indexes on the parent collection,
  #    irrespective of how STI is defined in Mongoid, i.e. ANY child index will be applied to EVERY child.
  #    This can cause collisions using various combinations of scopes.
  #
  # 3) Paranoid docs rely on sparse indexes to exclude paranoid-deleted records
  #    from the unique index constraint (i.e. when _slugs is unset.) However, when
  #    using compound keys (`by_model_type` or `scope_key`), paranoid-deleted records
  #    can become inadvertently indexed when _slugs is unset, causing duplicates. This
  #    is already covered by #1 and #2 above.
  #
  # In the future, MongoDB may implement partial indexes or improve sparse index behavior.
  # See: https://jira.mongodb.org/browse/SERVER-785
  #      https://jira.mongodb.org/browse/SERVER-13780
  #      https://jira.mongodb.org/browse/SERVER-10403
  options = {}
  unless scope_key || by_model_type
    options[:unique] = true
    options[:sparse] = true
  end

  [fields, options]
end