MongoDB

MongoDB is Warden’s second engine. Requests are command documents, not strings, and every guarantee is the same vocabulary PostgreSQL uses.


Versions	MongoDB 6.0+ (standalone or replica set)
Certification	Strict in CI against a single-node replica set — `wardencert -engine mongodb -strict` — plus live integration tests
Driver	`mongo-driver v2`

What it provides, and who provides it

Guarantee	Level	How
Record scoping	`enforced`	Lease bindings are conjoined into the document filter before it reaches the server
Field masking	`enforced`	Result-path masking before rows leave the gateway
Statement timeout	`native`	Context deadline derived from `statement_timeout_ms`; the server cancels on close
Attribution	`native`	Sanitised `comment` on every operation, visible in `currentOp`
Row limits	`enforced`	Limit injected into finds, re-capped in the gateway with honest truncation
Dry run	`enforced`	Count from the server plus sampled before/after images, at `estimated` fidelity; DDL reports `static`
Cost estimate	`advisory`	Counts only
Fence	`enforced`	Content hash over the targeted documents; on a replica set the staleness check and the write commit in one transaction, on standalone they run back-to-back
Per-agent identity	`enforced`	Gateway-side identity; no engine principal exists
Lease revocation	`enforced`	Sessions under a revoked lease are refused on next use
Transactional DDL	`unavailable`	MongoDB DDL is not transactional

Replica-set versus standalone is probed at connect time and recorded in the capability note. Standalone has no multi-document transactions, so fences and previews are content hashes rather than transactional guarantees.

Command grammar

{
  "verb": "find | insert | update | delete | create | drop | eval",
  "resource": "orders",
  "filter": {"id": "ord_1", "status": {"in": ["paid", "pending"]}},
  "set": {"status": "refunded"},
  "unset": ["note"],
  "fields": ["id", "status"],
  "documents": [{"id": "ord_1", "status": "paid"}],
  "from": "customers"
}

A value of the form "$N" references params[N]. Everything else is a literal. A key the verb does not use is refused, not ignored, so a find carrying set fails rather than passing review as a harmless read. Unknown filter operators become unparsed_construct and deny. A parameter holding a document or a list is refused as a filter value rather than executed: in that position the driver would read it as an operator.

Writes carry the scope too

Reads and deletes are restricted by conjoining the lease’s bindings into the filter. Writes are restricted by what they write: an insert must set every scoped field explicitly to the lease’s value, and an update may neither assign a scoped field a different value nor remove it. Anything else is refused rather than corrected, so the operation that executes is the one a reviewer approved.

Setting it up

connections:
  - name: shop
    engine: mongodb
    dsn: mongodb://warden_gateway:secret@mongo.internal:27017
    policy: ./policies/shop.yaml
    options:
      database: shop
      collections: orders,customers
      statement_timeout_ms: "5000"
      max_pool_size: "10"
      application_name: warden

Set database. It may also come from the DSN path, but an empty value is refused rather than inferred silently. Set collections on any non-trivial database; without it the catalog includes every collection.

Known gaps

Native per-lease principals. MongoDB users and roles exist, but this connector reports gateway-enforced identity honestly rather than minting database users per lease.
Relationship scoping is not supported.

How Warden works

Engines

What it provides, and who provides it

Command grammar

Writes carry the scope too

Setting it up

Known gaps

​What it provides, and who provides it

​Command grammar

​Writes carry the scope too

​Setting it up

​Known gaps

What it provides, and who provides it

Command grammar

Writes carry the scope too

Setting it up

Known gaps