_executeInTransaction (accessMode, work, transactionConfig) {
    const wrapper = txc => new RxManagedTransaction({
      run: txc.run.bind(txc)
    })
    return this._runTransaction(accessMode, work, transactionConfig, wrapper)
  }
@private
@param {function(txc: RxManagedTransaction): Observable} work
@param {TransactionConfig} transactionConfig
@returns {Observable}