How to sort data in Mongo in a custom order

Question

How I can sort this data, using Mongo functionality:

Input

{ "_id" : 1, "domainName" : "test1.com", "hosting" : "hostgator.com" }
{ "_id" : 2, "domainName" : "test2.com", "hosting" : "aws.amazon.com"}
{ "_id" : 3, "domainName" : "test3.com", "hosting" : "aws.amazon.com" }
{ "_id" : 4, "domainName" : "test4.com", "hosting" : "hostgator.com" }
{ "_id" : 5, "domainName" : "test5.com", "hosting" : "aws.amazon.com" }
{ "_id" : 6, "domainName" : "test6.com", "hosting" : "cloud.google.com" }
{ "_id" : 7, "domainName" : "test7.com", "hosting" : "aws.amazon.com" }
{ "_id" : 8, "domainName" : "test8.com", "hosting" : "hostgator.com" }
{ "_id" : 9, "domainName" : "test9.com", "hosting" : "cloud.google.com" }
{ "_id" : 10, "domainName" : "test10.com", "hosting" : "godaddy.com" }

In order by hosting field, to get result, for example in this order:

1) First - all godaddy;

2) Second - all AWS;

3) and next, everything else.

Output

{
    "result" : [
            {

                    "_id" : 10, 
                    "domainName" : "test10.com",
                    "hosting" : "godaddy.com"
            },
            {
                    "_id" : 2, 
                    "domainName" : "test2.com",
                    "hosting" : "aws.amazon.com"
            },
            {
                    "_id" : 3, 
                    "domainName" : "test3.com",
                    "hosting" : "aws.amazon.com"
            },
            {
                    "_id" : 5, 
                    "domainName" : "test5.com",
                    "hosting" : "aws.amazon.com"
            },
            {
                    "_id" : 7, 
                    "domainName" : "test7.com",
                    "hosting" : "aws.amazon.com"
            },
            {
                    "_id" : 1, 
                    "domainName" : "test1.com",
                    "hosting" : "hostgator.com"
            },
            {
                    "_id" : 4, 
                    "domainName" : "test4.com",
                    "hosting" : "hostgator.com"
            },
            {
                    "_id" : 6, 
                    "domainName" : "test6.com",
                    "hosting" : "cloud.google.com"
            },
            {
                    "_id" : 8, 
                    "domainName" : "test8.com",
                    "hosting" : "hostgator.com"
            },
            {
                    "_id" : 9, 
                    "domainName" : "test9.com",
                    "hosting" : "cloud.google.com"
            },
    ]
    }

With this example i want to return results in more relevant way for user. And in origanl task I want to sort this using few another collections, which serve additional information.

But will be good enough if you helps me with previous task?

UPD: About second part of question.

One more task is how to return sortable data from one collection in dependence of another.

Example:

first collection the same which was given before:

 { "_id" : 1, "domainName" : "test1.com", "hosting" : "hostgator.com" }
 ...

second collection, provide some additional info about hosting:

{ '_id': 123, 'quality':'best', 'hostings': ["hostgator.com",  "aws.amazon.com"]},
{ '_id': 321, 'quality':'good', 'hostings': ["cloud.google.com"]},
{ '_id': 345, 'quality':'bad', 'hostings': ["godaddy.com"]},

And in result, I need to return from first collection data in this order:

1) First all good hostings 2) second all good 3) third all bad

Output:

{
"result" : [
        //Best:
        {
                "_id" : 1, 
                "domainName" : "test1.com",
                "hosting" : "hostgator.com"
        },
        {
                "_id" : 4, 
                "domainName" : "test4.com",
                "hosting" : "hostgator.com"
        },
        {
                "_id" : 8, 
                "domainName" : "test8.com",
                "hosting" : "hostgator.com"
        },
        {
                "_id" : 2, 
                "domainName" : "test2.com",
                "hosting" : "aws.amazon.com"
        },
        {
                "_id" : 3, 
                "domainName" : "test3.com",
                "hosting" : "aws.amazon.com"
        },
        {
                "_id" : 5, 
                "domainName" : "test5.com",
                "hosting" : "aws.amazon.com"
        },
        {
                "_id" : 7, 
                "domainName" : "test7.com",
                "hosting" : "aws.amazon.com"
        },

       // Good:
        {
                "_id" : 9, 
                "domainName" : "test9.com",
                "hosting" : "cloud.google.com"
        },
        {
                "_id" : 6, 
                "domainName" : "test6.com",
                "hosting" : "cloud.google.com"
        },

       //Bad
        {
                "_id" : 10, 
                "domainName" : "test10.com",
                "hosting" : "godaddy.com"
        }
]
}

UPDATE 2

I get good answer and example on previous example. Thank you so much! But I stack with another example.

I need to compare IDs of 3 collections to sort in order - first: friend, second: 'requests', and: other users.

Input

db.friends.find({userId: currentUser});
    // {"_id" : "PgC7LrtaZtQsShtzT", "userId" : "tHuxnWxFLHvcpRgHb", "friendId" : "jZagPF7bd4aW8agXb",}
db.requests.find({userId: currentUser});
   // looks like friend but with 'requesterId'

And now I need to aggregate 'users' collection, define the score which matches with previous two collections (friends, requests).

Using provided answer, I managed result but only with one collection. How can I make this with 3 or multiple?

Answer 1

You can project each of the hosting into separate type denoted by integers, and finally sort on these integers. Illustrated in the aggregation pipeline below

[
{$lookup: {
    from: 'secondCollectionStoringQuality',
    localField: 'hosting',
    foreignField: 'hostings',
    as: 'nw'
    }},
{$unwind: '$nw'},
{$project: {
        domainName: 1,
        hosting: 1,
        type: {
            $cond: [
                {$eq: ['$nw.quality', 'best']},
                0,
                {$cond: [
                    {$eq: ['$nw.quality', 'good']},
                    1,
                    2
                    ]}
            ]
        }
    }},
    {$sort: {type: 1}}
]