/** @return undefined if cannot find _id */
export declare function getId(obj: any): string | undefined;
/** Merge filter with correct handling of OR and AND
 * @param {Object} filterA
 * @param {Object} filterB
 * @param {Boolean} assignToFilterA defualt false: if true, it will modify filterA, else it will return merged filters as a new object
 */
export declare function mongoFilterMerger(filterA: any, filterB: any, assignToFilterA?: boolean): any;
export declare function mongoPush(field: string, value: any, fields: {
    [k: string]: any;
}): void;