Insert copy of document into same document for versioning

[John Menke]

We have a requirement for versioning that expects prior versions of a document to be stored in a version array within the document. Is it possible to both update fields in a document and save a copy of the document itself in a single operation?

All I want to do is append to the version array i don't want to have to copy down to client and update.

[Allan Bazinet]

It sounds as if the requirement here is that the document must contain, within the document itself, an array that contains all previous versions of the document, which would include the array.

While I can't think of any way to do this without reading the document, I think the key thing here is that you're looking at exponential growth there, which does get out of hand quite quickly.  For example, consider a relatively small, 1K document; even with zero growth, at 14 revisions, you're at the document maximum size limit.

In cases where we've needed something like that, we've used a separate collection to store the versions, with documents containing two fields, a 'link' field, with the oid of the originating document, and a 'data' field, with the original contents, so as to handle the unbounded requirement without needing to worry about hitting the maximum document size limit.  With an index on the link field, it's straightforward to use.  Some of the drivers, such as mongoose, have a 'populate' function that makes getting the current version of the document from the link field easy.

[Rhys Campbell]

Maximum document size is 16MB https://docs.mongodb.org/manual/refere nce/limits/

[John Menke]

looking at the update operators.  even though i can append to an array i am not sure i can get a reference to the current document inside an update.  I don't see an operator that give this reference.  Is there an operator that gives reference to current document in update?

Update Operators

Fields

Name	Description
$inc	Increments the value of the field by the specified amount.
$mul	Multiplies the value of the field by the specified amount.
$rename	Renames a field.
$setOnInsert	Sets the value of a field if an update results in an insert of a document. Has no effect on update operations that modify existing documents.
$set	Sets the value of a field in a document.
$unset	Removes the specified field from a document.
$min	Only updates the field if the specified value is less than the existing field value.
$max	Only updates the field if the specified value is greater than the existing field value.
$currentDate	Sets the value of a field to current date, either as a Date or a Timestamp.

Array

Operators

Name	Description
$	Acts as a placeholder to update the first element that matches the query condition in an update.
$addToSet	Adds elements to an array only if they do not already exist in the set.
$pop	Removes the first or last item of an array.
$pullAll	Removes all matching values from an array.
$pull	Removes all array elements that match a specified query.
$pushAll	Deprecated. Adds several items to an array.
$push	Adds an item to an array.

Modifiers

Name	Description
$each	Modifies the $push and $addToSet operators to append multiple items for array updates.
$slice	Modifies the $push operator to limit the size of updated arrays.
$sort	Modifies the $push operator to reorder documents stored in an array.
$position	Modifies the $push operator to specify the position in the array to add elements.