t8y2/dbx · error · java.lang.IllegalArgumentException

MongoDB createUser user document contains reserved command…

Error message

MongoDB createUser user document contains reserved command fields

What it means

The agent assembles the createUser command itself, so the user_json document must not contain the command fields "createUser" or "writeConcern" — including them would either duplicate the command name or conflict with the write concern the agent attaches. buildCreateUserCommand rejects such documents with IllegalArgumentException.

Solutions

1. Remove the "createUser" field from user_json — the agent adds it from the "user" value.
2. Remove "writeConcern" from user_json and pass it via the write_concern_json parameter instead.
3. Keep user_json to user attributes only: pwd, roles, customData, mechanisms, etc.

Example fix

// before
{"user_json": {"createUser": "bob", "pwd": "x", "writeConcern": {"w": 1}}}
// after
{"user_json": {"user": "bob", "pwd": "x"}, "write_concern_json": {"w": 1}}

const reserved = ["createUser", "writeConcern"];
for (const k of reserved) {
  if (params.user_json && k in params.user_json) {
    throw new Error("Remove reserved field '" + k + "' from user_json");
  }
}

function hasNoReservedFields(userJson) {
  return userJson == null || (!("createUser" in userJson) && !("writeConcern" in userJson));
}

try {
  await agent.createUser({ database, user_json: doc });
} catch (e) {
  if (String(e.message).includes("reserved command fields")) {
    const { createUser, writeConcern, ...clean } = doc;
    await agent.createUser({ database, user_json: clean, write_concern_json: writeConcern });
  } else throw e;
}

When it happens

Trigger: Passing a full server-style command document as user_json, e.g. {"createUser": "bob", "pwd": "...", "roles": [...]}, or including a "writeConcern" key inside user_json.

Common situations: Copying a mongosh/db.createUser command document verbatim into user_json; migrating scripts that previously sent raw runCommand payloads; supplying writeConcern in the wrong place (it belongs in the top-level write_concern_json parameter).

Related errors

• MongoDB createUser requires a non-empty user name
• agentSessionId is required
• arrayFilters must be an array
• Bulk update requires update operators such as $set
• dropIndex does not accept "*"; use dropIndexes() or…

AI-assisted analysis of t8y2/dbx@c0390bff16 (2026-09-05). Data as JSON: /api/errors/c608f5bd7c017db0. Report an issue: GitHub.

Appendix: source

Thrown at agents/drivers/mongodb/src/main/java/com/dbx/agent/mongodb/MongoAgent.java:1048

        );
        return Collections.singletonMap("name", name);
    }

    private static Object createUser(JsonObject params) {
        MongoClient client = requireClient();
        String database = params.get("database").getAsString();
        client.getDatabase(database).runCommand(buildCreateUserCommand(params));
        return Collections.singletonMap("affected_rows", 1);
    }

    static Document buildCreateUserCommand(JsonObject params) {
        Document user = requiredDocument(params, "user_json", "User document");
        Object username = user.remove("user");
        if (!(username instanceof String) || ((String) username).isBlank()) {
            throw new IllegalArgumentException("MongoDB createUser requires a non-empty user name");
        }
        if (user.containsKey("createUser") || user.containsKey("writeConcern")) {
            throw new IllegalArgumentException("MongoDB createUser user document contains reserved command fields");
        }

        Document command = new Document("createUser", username);
        command.putAll(user);
        Document writeConcern = documentOrNull(params, "write_concern_json");
        if (writeConcern != null) {
            command.put("writeConcern", writeConcern);
        }
        return command;
    }

    private static Document requiredDocument(JsonObject params, String key, String label) {
        Document document = documentOrNull(params, key);
        if (document == null) {
            throw new IllegalArgumentException(label + " are required");
        }
        return document;
    }

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