mongodb/node-mongodb-native · error · MongoInvalidArgumentError

ClientSession must be from the same MongoClient

Error message

ClientSession must be from the same MongoClient

What it means

executeOperation (src/operations/execute_operation.ts:95) throws a MongoInvalidArgumentError when the ClientSession supplied to an operation was created by a different MongoClient instance (session.client !== client). Sessions are bound to the client that created them because they carry cluster time, server pinning, and transaction state tied to that client's topology.

Source

Thrown at src/operations/execute_operation.ts:95

      : client.topology;

  // The driver sessions spec mandates that we implicitly create sessions for operations
  // that are not explicitly provided with a session.
  let session = operation.session;
  let owner: symbol | undefined;

  if (session == null) {
    owner = Symbol();
    session = client.startSession({ owner, explicit: false });
  } else if (session.hasEnded) {
    throw new MongoExpiredSessionError('Use of expired sessions is not permitted');
  } else if (
    session.snapshotEnabled &&
    maxWireVersion(topology) < MIN_SUPPORTED_SNAPSHOT_READS_WIRE_VERSION
  ) {
    throw new MongoCompatibilityError('Snapshot reads require MongoDB 5.0 or later');
  } else if (session.client !== client) {
    throw new MongoInvalidArgumentError('ClientSession must be from the same MongoClient');
  }

  operation.session ??= session;

  const readPreference = operation.readPreference ?? ReadPreference.primary;
  const inTransaction = !!session?.inTransaction();

  const hasReadAspect = operation.hasAspect(Aspect.READ_OPERATION);

  if (
    inTransaction &&
    !readPreference.equals(ReadPreference.primary) &&
    (hasReadAspect || operation.commandName === 'runCommand')
  ) {
    throw new MongoTransactionError(
      `Read preference in a transaction must be primary, not: ${readPreference.mode}`
    );
  }

View on GitHub (pinned to 3366c21a63)

Solutions

1. Ensure the session is created by the same MongoClient whose collection/db you are calling the operation on.
2. Pass the client explicitly or derive sessions from the client that owns the collection.
3. Audit code where multiple MongoClient instances coexist and verify session provenance.

Example fix

// before
const session = clientA.startSession();
await clientB.db('app').collection('users').insertOne({}, { session }); // throws

// after
const session = clientB.startSession();
await clientB.db('app').collection('users').insertOne({}, { session });

function assertSessionOwner(session: ClientSession, client: MongoClient): void {
  if (session.client !== client) {
    throw new Error('Session was created by a different MongoClient');
  }
}
// usage:
assertSessionOwner(session, client);

const sessionBelongsTo = (session: ClientSession, client: MongoClient): boolean =>
  session.client === client;

When it happens

Trigger: Creating a session with clientA.startSession() and passing it to a collection or operation obtained from clientB (a different MongoClient).

Common situations: Multi-tenant applications with one client per tenant, connection-pool reuse bugs, or refactors that swap MongoClient instances without updating session creation.

Related errors

• Unexpected null session. A cursor creating command should ha
• Unexpected null session. A cursor creating command should ha
• Missing required callback parameter
• Use of expired sessions is not permitted
• Snapshot reads require MongoDB 5.0 or later

AI-assisted analysis of mongodb/node-mongodb-native@3366c21a63 (2026-08-04). Data as JSON: /data/errors/9a4f2ef0efba36d8.json. Report an issue: GitHub.