{"record":{"id":"3c0ecf8bb2e36854","repo":"mongodb/node-mongodb-native","slug":"loadbalanced-option-not-supported-when-directconne","errorCode":null,"errorMessage":"loadBalanced option not supported when directConnection is provided","messagePattern":"loadBalanced option not supported when directConnection is provided","errorType":"exception","errorClass":"MongoParseError","httpStatus":null,"severity":"error","filePath":"src/connection_string.ts","lineNumber":577,"sourceCode":" * - directConnection is set\n * - if srvMaxHosts is used when an srv connection string is passed in\n *\n * @throws MongoParseError\n */\nfunction validateLoadBalancedOptions(\n  hosts: HostAddress[] | string[],\n  mongoOptions: MongoOptions,\n  isSrv: boolean\n): void {\n  if (mongoOptions.loadBalanced) {\n    if (hosts.length > 1) {\n      throw new MongoParseError(LB_SINGLE_HOST_ERROR);\n    }\n    if (mongoOptions.replicaSet) {\n      throw new MongoParseError(LB_REPLICA_SET_ERROR);\n    }\n    if (mongoOptions.directConnection) {\n      throw new MongoParseError(LB_DIRECT_CONNECTION_ERROR);\n    }\n\n    if (isSrv && mongoOptions.srvMaxHosts > 0) {\n      throw new MongoParseError('Cannot limit srv hosts with loadBalanced enabled');\n    }\n  }\n  return;\n}\n\nfunction setOption(\n  mongoOptions: any,\n  key: string,\n  descriptor: OptionDescriptor,\n  values: unknown[]\n) {\n  const { target, type, transform } = descriptor;\n  const name = target ?? key;\n","sourceCodeStart":559,"sourceCodeEnd":595,"githubUrl":"https://github.com/mongodb/node-mongodb-native/blob/dce7939f86fb283e167ad709955abedb7bf23124/src/connection_string.ts#L559-L595","documentation":"Thrown by MongoParseError (constant LB_DIRECT_CONNECTION_ERROR) at src/connection_string.ts:577 when both `loadBalanced=true` and `directConnection=true` are set. The two are incompatible topologies: directConnection bypasses SDAM against one server, while loadBalanced expects a single SDAM-managed endpoint behind a LB.","triggerScenarios":"URI `...?loadBalanced=true&directConnection=true` or options `{ loadBalanced: true, directConnection: true }`.","commonSituations":"Combining flags while experimenting; copying both options from docs/Stack Overflow examples into the same URI.","solutions":["Use only `loadBalanced=true` (remove directConnection) for an LB fronted deployment.","Use only `directConnection=true` (remove loadBalanced) to pin a single server without SDAM."],"exampleFix":"// before\nnew MongoClient('mongodb://host:27017/?loadBalanced=true&directConnection=true')\n\n// after\nnew MongoClient('mongodb://host:27017/?loadBalanced=true')","handlingStrategy":"validation","validationCode":"function assertNoLbPlusDirect(options = {}, uri = '') {\n  const lb = options.loadBalanced ?? /loadBalanced=true/i.test(uri);\n  const dc = options.directConnection ?? /directConnection=true/i.test(uri);\n  if (lb && dc) throw new Error('loadBalanced and directConnection cannot both be set.');\n}","typeGuard":null,"tryCatchPattern":"try { new MongoClient(uri, options); } catch (e) { if (e instanceof MongoParseError && /loadBalanced option not supported when directConnection/.test(e.message)) { delete options.directConnection; } else throw e; }","preventionTips":["Maintain an allow-list of option combinations; reject conflicting topology flags at config-load time.","Document which topology each flag belongs to so operators do not stack them."],"tags":["connection-string","load-balanced","direct-connection","topology"],"backgroundTag":null,"analyzedSha":"dce7939f86fb283e167ad709955abedb7bf23124","analyzedAt":"2026-08-11T04:54:53.215Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}