update(mergeObj) {
        const { session, modelName: table } = this.modelClass;

        session.applyUpdate({
            action: UPDATE,
            query: {
                table,
                clauses: this.clauses,
            },
            payload: mergeObj,
        });

        this._evaluated = false;
    }
Records an update specified with `mergeObj` to all the objects
in the {@link QuerySet} instance.

@param  {Object} mergeObj - an object to merge with all the objects in this
                            queryset.
@return {undefined}