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DOCS-1411: Clarifications on BSON field ordering #1220

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DOCS-1411: Clarifications on BSON field ordering #1220

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12 changes: 11 additions & 1 deletion source/core/document.txt
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Expand Up @@ -108,12 +108,22 @@ existing user document.
Document Limitations
--------------------

Record documents have the following attributes:
Documents have the following attributes:

- .. include:: /includes/fact-document-max-size.rst

- .. include:: /includes/fact-document-field-name-restrictions.rst

- MongoDB does not make guarantees regarding the order of fields in
a BSON document. Drivers and MongoDB will reorder the fields of a
documents upon insertion and following updates.

Most programming languages represent BSON documents with some form
of :term:`mapping type <mapping types>`. Comparisons between mapping typed objects
depend on order. As a result, the only way to ensure that two
documents have the same set of field and value pairs is to compare
each field and value individually.

The ``_id`` Field
-----------------

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8 changes: 8 additions & 0 deletions source/reference/glossary.txt
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Expand Up @@ -383,6 +383,14 @@ Glossary
management. For information on LVM and MongoDB, see
:ref:`lvm-backup-and-restore`.

mapping types
Structures in programming languages that associate keys with
values, where keys may nest other pairs of keys and values
(e.g. dictionaries, hashes, maps, and associative arrays).
The properties of these structures depend on the language
specification and implementation. But generally these structures
are not strictly ordered.

map-reduce
A data processing and aggregation paradigm consisting of a "map"
phase that selects data and a "reduce" phase that transforms the
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