Given a MongoDB router like the BigsRouter in JavaScript below explain what that router is doing, what it needs, and it$$s data access pattern.

import $\{$ Router $\}$ from "express";

import $\{$ ObjectId $\}$ from "mongoallData";

import SmallsRouter from $"./$smalls$.$js$"$;

const BigsRouter $=$ Router$()$;

BigsRouter.use$("/$:bigId$/$smalls$",$ SmallsRouter$)$;

BigsRouter.get$("/",$ async $($req$,$ res$)=>\{$

const smalls $=$ await allData.collection$("$bigs$").$find$().$toArray$()$;

const allData $=$ req.app.get$("$allData$")$;

return res.json$($smalls$)$;

$\})$;

BigsRouter.get$("/$:id$",$ async $($req$,$ res$)=>\{$

const allData $=$ req.app.get$("$allData$")$;

const small $=$ await allData.collection$("$bigs$").$findOne$(\{\_$id: new ObjectId$($req$.$params.id$)\})$;

return res.json$($small$)$;

$\})$;

BigsRouter.post$("/",$ async $($req$,$ res$)=>\{$

const allData $=$ req.app.get$("$allData$")$;

$\})$;

BigsRouter.put$("/$:id$",$ async $($req$,$ res$)=>\{$

req.body.$\_$id $=$ new ObjectId$($req$.$params.id$)$;

const allData $=$ req.app.get$("$allData$")$

return res.status$(201).$end$()$;

$\})$;

BigsRouter.delete$("/$:id$",$ async $($req$,$ res$)=>\{$

const allData $=$ req.app.get$("$allData$")$;

return res.status$(201).$end$()$;

$\})$;

export default BigsRouter;