subtract-query-filter

Use case

You need to fetch a lot of data from a remote server (with a filter that is defined on client-side and executed on server-side).

You want to fetch additional data of the same type, but you do not want to load documents a second time.

You could now include something like { _id: { $nin: [ ... a lot of ids ] } } to your filter.

This package offers a different approach: You just have to subtract the previously used filter from your new one.

Example

You implemented a calender with a day- and a month-view. There are a lot of events each there (therefore its expensive to exclude already fetched ids from new queries).

The user navigates through the app:

Time span fetched	Internal query	Query to server
02.01.	{date: {$in: [02.01.]}	{date: {$in: [02.01.]}
01.01. - 07.01.	{date: {$gte: '01.01.', $lte: '07.01.'	{date: {$gte: '01.01.', $lte: '07.01.', $nin: [02.01.]
04.01. - 10.01.	{date: {$gte: '04.01.', $lte: '10.01.'	{date: {$gt: '07.01.', $lte: '10.01.'}

When to use

All of this does only make since if you need to fetch a lot of data or really must reduce the transferred data to a minimum.

If you don't, you might want to just fetch that data a second time.

Requirements / Interface

export type FilterConstraint = {
    $in?: any[];
    $nin?: any[];
    $lt?: any;
    $gt?: any;
    $lte?: any;
    $gte?: any;
}
 
export interface Filter {
    [key: string]: FilterConstraint;
}

The operations are restricted to the above.

{ $eq: VAL } must be expressed as { $in: [ VAL ] }.

{ $ne: VAL } must be expressed as { $nin: [ VAL ] }.

So far, it is not possible to use query operators like $and, $or, $all etc...

How to use