How can I return only the string value of an object from a MongoDB array

Question

valueOf() returns this:

[
   {},
   { toUser: '5ed9d49c7e516616600eb693' },       
   { toUser: '5ed9d49c7e516616600eb693' },       
   { toUser: '5ed9d49c7e516616600eb693' },       
   { toUser: '5ed9d3897e516616600eb692' }        
]

I want to return only the value like "5ed9d3897e516616600eb692" or whatever toUser has. How?

Answer 1

This can be done in a couple of different ways, the best of which is using distinct :

db.collection.distinct("toUser")

Output will be:

[
    '5ed9d49c7e516616600eb693',
    '5ed9d49c7e516616600eb693',
    '5ed9d49c7e516616600eb693',
    '5ed9d3897e516616600eb692'
]

Answer 2

You can use reduce and inside callback check if the object has any key using Object.keys and length. If it has k then push the value using Object.values into the accumulator array

 let data = [{}, { toUser: '5ed9d49c7e516616600eb693' }, { toUser: '5ed9d49c7e516616600eb693' }, { toUser: '5ed9d49c7e516616600eb693' }, { toUser: '5ed9d3897e516616600eb692' } ]; let filterdValue = data.reduce((acc, curr) => { const objKey = Object.keys(curr); if (objKey.length > 0) { acc.push(...Object.values(curr)) } return acc; }, []); console.log(filterdValue)

Answer 3

You can use following query to convert object to string

> db.objectidToStringDemo.aggregate([{$project: {toUser: {$toString: "$toUser"}}}]);