adilfaiz001 / learning-hub Goto Github PK

14th Dec, 2020

constructor
If this is part of parent and parent loads then irrespective of a child being routed or not, constructor loaded.

onInit
Function loaded on create a view as if parent loaded or not, it doesn't effect child.

MONGODB UNIVERSITY - M121

REFERENCE
https://stackoverflow.com/questions/29634150/updating-nested-array-inside-array-mongodb, https://www.nodechef.com/docs/cloud-search/updates-documents-nested-in-arrays

PROBLEM
Updating value of key in a object which is part if nested array, e.g.

Updating value of status inside double nested array

SOLUTION

When one schema is using reference to other schema and other schema is using nested level of reference, -

QUERY EXPLANATION
In above query, KEY company is being populated and KEY company_details is selected and further populated, from which KEY followers is selected, which is array of REF OBJECTID to another schema of users, therefore, its being populated as followers.user

company: {
   company_details: {
      followers: {
            user: [{ref: OBJECTID}]
      }
    }
}

USE CASE

New comment to be added to the comments document in an array, so using findByIdAndUpdate with query function $push to add element in the array. This successfully added the comment in the document and return whole comments document with array of comment objects

ISSUE

There is no reference to the comment in an array which comment is added(as of now, its push method on an array, so it is last element) but thinking of issue like in future when multiple user comment on same post, will this query return updated array, example : user_1 commented and query adding and returning it while user_2 at same commented on this and user_1 query return a new updated array, will this array last element be user_1 or user_2 ?

SOLUTION

1. Using saving id at the time of updating to refer on the event of returning new set on query findAndUpdate
2. NEED TO FIND : Does findAndUpdate returns the only updating array of anything at the time of querying it, example user_1 update it, so this query returns only upto this user, whats happening to this doc at other user end, wont affect at user_1 end.

19th Nov, 2020

Selecting all documents of a collection and grouping them by a key and pushing all document of that particular key into a array, against that key_

RESULT:

[
  {
    company: "ABC",
    product: [
        {product_1},
        {product_2}
    ]
  }
]

NOTE: Use $$ROOT for pushing complete document into array in parallel with a key which is aggregate by group

1. Sending Array in HTTP Request

DOING
Sending Array in POST Request and server receives this as string, parsing array using middlewares/parsers and then using it.

STANDARD