mongoose breaking changes

9.7.2

1 breaking change, first published June 22, 2026.

• Behavior changed
  Schema type lookups now ignore inherited properties, and setting schema paths under special property names is disallowed. Code that relied on either behavior should be checked. github.com

9.7.0

5 breaking changes, first published June 9, 2026.

• Behavior changed
  Assigning over an array that was selected with $slice now throws instead of proceeding silently. Code that overwrites such arrays must be changed. github.com
• Behavior changed
  Primitive values inside union types are now cast when documents are created, which can change stored values for existing code. github.com
• Behavior changed validateSync
  validateSync() no longer uses the union fallback, so union-typed fields may now fail validation where they previously passed. github.com
• Signature changed 'mongoose'.ApplyBasicCreateCasting
  Was type ApplyBasicCreateCasting<T> = {[K in keyof T]: NonNullable<T[K]> extends Map<infer KeyType extends string, infer ValueType> ? (Record<KeyType, ValueType> | Array<[KeyType, ValueType]> | T[K]) : NonNullable<T[K]> extends... npmjs.com
• Signature changed 'mongoose'.Document.validateSync
  Was validateSync(options: ValidateOptions & {[k: string]: any}): Error.ValidationError | null validateSync(pathsToValidate?: pathsToValidate, options?: Omit<ValidateOptions, 'pathsToSkip'> & AnyObject): Error.ValidationError | null... npmjs.com

Check your code

These are the changes. To see which of them reach your code, scan a public repository, or have your coding agent call check_code with your manifest or lockfile over MCP. The API reads every change in every version, not only the newest. On Team and up, a fix pull request opens for the changes that reach a connected repository. Nothing merges or deploys.