MongoDB query on multiple array of objects

Question

Say I have a mongoSchema of user with the following field

googleId: String,
name: String,
Language : [{}],

User can initially specify an array of language-set [up to 5] on their profile page.

For example, user can have 2 language set as below:

Language :

[main: {name: English, code: ko}, secondary: [{name:Japanese, code: jp}, {name:Chinese, code: en}]], 

[main: {name: Korean, code: ko}, secondary: [{name:Japanese, code: jp}, {name:English, code: en}]

From this information, I want to render out only the post that matches the following preference.

For example post with English to Japanese, English to Chinese (from first language set)

as well as post with Korean to Japanese, Korean to English (from second language set)

My post schema has

    postName: String
    original: {},
    target: {},

For example,

postName: 'Korean to Japanese Post'
original: {name: Korean, code: ko}
target: {name: Japanese, code jp}

What should I put inside the curly brackets to fetch the posts with specified language set

const prefLang = req.user.Language
const post = await Post.find({ some query using prefLang to check over matching original and target })
res.send(translations)

(1.) Is the actual schema of the field Language defined as in your code? because main: [Object] would mean array of objects and [Array] would mean array of arrays. (2.) Also, your in your example, secondary should have multiple objects right? currently you have a single objects with duplicate keys. (3.) your post schema has original and target, but your did not mention about user.original and user.target so what is req.user.original and req.user.target? Isn't it supposed to be user.Language? — thammada.ts
– thammada.ts, Commented Jul 12, 2020 at 8:21
1. Sorry I printed the console.log. In schema it is defined as Language: [{}] 2. Yes it should be multiple [{name: Japanese, code:jp}, {name:Chinese, code: ch}] 3) I should just have const prefLanguage = req.user.Language. Sorry I'll edit this info — Min
– Min, Commented Jul 12, 2020 at 8:47

thammada.ts · Accepted Answer · 2020-07-12 09:28:37Z

The query object should look like this for your example

{
  $or: [
    {
      original: { name: "English", code: "en" },
      target: {
        $in: [{ name: "Japanese", code: "jp" }, { name: "Chinese", code: "cn" }]
      }
    },
    {
      original: { name: "Korean", code: "ko" },
      target: {
        $in: [{ name: "Japanese", code: "jp" }, { name: "English", code: "en" }]
      }
    }
  ]
}

So you will have to construct the condition from prefLang like this

const query = {
  $or: perfLang.map(lang => ({
    original: lang.main,
    target: { $in: lang.secondary }
  }))
}

const post = await Post.find(query)

Tip:

If the language objects have a strict schema, you can define them like this

const LanguageSchema = new mongoose.Schema({
  name: String,
  code: String
}, {
  _id: false
})

const UserSchema = new mongoose.Schema({
  //...
  googleId: String,
  name: String,
  Language: [{ main: LanguageSchema, secondary: [LanguageSchema] }]
})

Tom Slabbaert · Accepted Answer · 2020-07-12 09:18:18Z

1

Sounds like the usage of basic boolean logic would suffice:

const prefLang = req.user.Language;

let conditions = [];

prefLang.forEach((langObj) => {
    let tragetLangs = langObj.secondary.map(lang => lang.code);
    conditions.push({
        $and: [
            {
                "original.code": langObj.main.code,
            },
            {
                "target.code": {$in: tragetLangs}
            }
        ]
    })
})

// you should check conditions !== empty array.
const post = await Post.find({$or: conditions})

edited Jul 12, 2020 at 9:18

answered Jul 12, 2020 at 9:01

Tom Slabbaert

22.5k10 gold badges35 silver badges45 bronze badges

8 Comments

Min Over a year ago

Wouldn't this only list out the post that matches the first set? I could have up to 5 language set. I want to go over all of them.

Tom Slabbaert Over a year ago

Then I misunderstood the data structure, is prefLange a list of those objects as i specified in the comment?

Min Over a year ago

yes it's a list of the language set object. Sorry i didn't make this clear

Tom Slabbaert Over a year ago

I edited my answer to support an array, the logic is still the similar but we do an $or over the conditions built as there can be multiple.

Tom Slabbaert Over a year ago

You can't add a custom sort like that using find, even if you use aggregate you'll still have to manually add a place holder field like kr_sort: 1, jp_sort: 2 and only then you'll be able to sort on that, i'm going to add a simple aggregation that starts with the user to show it.

|

Collectives™ on Stack Overflow

MongoDB query on multiple array of objects

2 Answers 2

Comments

8 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

8 Comments

Your Answer

Sign up or log in

Post as a guest

Related