Major - P3 The current PartialValueStrategy creates full documents which are then used in the ReplaceOneBusinessKeyStrategy. This is fine if the document are an exact match, but if there are extra fields in a document then there won't be a match, which can lead to duplicate key errors.
MongoDB Enterprise > db.test.insert({"a": {"a1": 1}, b: {b1: 1, b2: 1}})
MongoDB Enterprise > db.test.insert({"a": {"a1": 1}, b: {b1: 1, b2: 1, c1: 1}})
// Document notation matches one record
MongoDB Enterprise > db.test.find({a: {a1: 1}, b: {b1: 1, b2: 1}})
{ "_id" : ObjectId("5f5740a32d2c3b0aec9e0e49"), "a" : { "a1" : 1 }, "b" : { "b1" : 1, "b2" : 1 } }
// Dot notation matches all records.
MongoDB Enterprise > db.test.find({"a.a1": 1, "b.b1": 1, "b.b2": 1})
{ "_id" : ObjectId("5f5740a32d2c3b0aec9e0e49"), "a" : { "a1" : 1 }, "b" : { "b1" : 1, "b2" : 1 } }
{ "_id" : ObjectId("5f5740a92d2c3b0aec9e0e4a"), "a" : { "a1" : 1 }, "b" : { "b1" : 1, "b2" : 1, "c1" : 1 } }