DOC: explain bson dependency to avoid confusion

conda-recipe/meta.yaml

@@ -33,6 +33,7 @@ requirements:
   run-constrained:
   - psdm_qs_cli >=0.3.1
   - pymongo >=4.0.2
+  # - bson  # bson is vendored by pymongo, and should not be installed separately
 
 test:
   commands:

dev-requirements.txt

@@ -4,6 +4,8 @@ ipython
 matplotlib >=3.2.0
 ophyd >=1.5.0
 pymongo
+# bson is vendored by pymongo, and should not be installed separately
+# bson
 pcdsutils
 pcdsdevices
 mongomock >=3.22.0

docs/source/upcoming_release_notes/333-doc_bson_not_req.rst

@@ -0,0 +1,23 @@
+333 doc_bson_not_req
+####################
+
+API Changes
+-----------
+- N/A
+
+Features
+--------
+- N/A
+
+Bugfixes
+--------
+- N/A
+
+Maintenance
+-----------
+- Documents bson dependency.  Bson is vendored by pymongo, which instructs
+  users to not install bson from pypi (`pymongo readme <https://github.com/mongodb/mongo-python-driver/tree/master#installation>`)
+
+Contributors
+------------
+- tangkong

happi/backends/mongo_db.py

@@ -5,13 +5,18 @@
 import re
 from typing import Any, Optional, Union
 
-import bson.regex
 from pymongo import MongoClient
 from pymongo.errors import OperationFailure, ServerSelectionTimeoutError
 
 from ..errors import DatabaseError, DuplicateError, SearchError
 from .core import ItemMeta, ItemMetaGen, _Backend
 
+try:
+    import bson.regex
+except ImportError:
+    raise ImportError('Optional dependency mongodb not found; mongodb backend'
+                      'is not available.  (bson not found)')
+
 logger = logging.getLogger(__name__)