import type { Knex } from 'knex';
import type { ModelCastType } from '../types';
export type ExpressionRelationConfig = {
    relation: string;
    fn: 'count' | 'sum' | 'avg' | 'min' | 'max';
    column?: string | Knex.Raw;
    cast?: ModelCastType;
    callback?: (q: any) => void;
};
export type ExpressionCallback = (db: any, parentTable: string) => any;
export declare function Expression(config: ExpressionRelationConfig | ExpressionCallback, castOption?: ModelCastType): (target: any, key: string) => void;