code: function (connection, uid, config) {
          if (!uid) {
              throw new AdapterError(AdapterError.TRANSACTION_ID_NOT_FOUND);
          }
  
          if (!config) {
              throw new AdapterError(AdapterError.TRANSACTION_CONFIG_NOT_FOUND);
          }
  
          if (connection.transactionId && Transaction.connections[connection.transactionId]) {
              throw new AdapterError(AdapterError.TRANSACTION_CONNECTION_OVERLAP);
          }
  
          // save all much needed info with the connection itself. remember to delete during disassociation
          connection.transactionId = uid;
          connection.transactionConfig = config;
  
          Transaction.connections[connection.transactionId] = connection;
      }
docs: Update the internal cache to associate a connection with a particular transaction id
  @private
  
  @param {mysql.Connection} connection
  @param {string} uid
  @param {Object} config