how to find all if the array is empty, mongodb

Question

i am trying to do some queries to my db... but i am new in mongodb and i dont know what operator i have to use, or maybe i just do not know how to do it.

i have a collection like this.

const userSchema= new Schema({
    user: { type: String },
    object: { type: String }
})

then i receive in my server a query like this

{
users: ['John', 'Michael', 'Peter'],
objects: ['Object1','Object2','Object3','Object4', 'Object5']
}

so.. in my controller i do this to find...

userModel.find({ user: { $in: req.body.users}, object: { $in: req.body.objects})
        .then((users)=>{
          res.json(users)
        })

Ok, this is working... but, in the case that one of the arrays Users or Objects is empty, it doesn't find nothing... so, how i can handle it? there is any operator that can find all if the array is empty or something?

for example.. if the query comes like this.

{
users: ['John', 'Michael', 'Peter'],
objects: []
}

i would like to find the users in my Users array even if i dont receive any object.

Any help? thank you in advance

with the $or operator i dont get the result that i expect, because it finds all users and all objects in the model and i just want to find the users that has those objects... damn sorry maybe i am not explaining it well — Sergio Cano
– Sergio Cano, Commented Mar 17, 2019 at 14:15

Ashh · Accepted Answer · 2019-03-17 15:07:25Z

2

You have to create custom match criteria

const query = {
  fieldName: { $gte: ..., $lte: ... }
}
if (req.body.users.length > 0) {
  query.users = req.body.users
}
if (req.body.objects.length > 0) {
  query.objects = req.body.objects
}

userModel.find(query).then((users) => {
  console.log(users)
})

edited Mar 17, 2019 at 15:07

answered Mar 17, 2019 at 14:21

Ashh

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6 Comments

Sergio Cano Over a year ago

but.. if req.body.users and objects is an array??

Ashh Over a year ago

So what? Please try it and then ask a question.

Sergio Cano Over a year ago

thank you, it works! but i have other question... in case that i want to filter in a date range... i am using { $gte : date: req.body.dateFrom, $lt: date: req.body.dateTo } ... How can i add it to this query object?

Ashh Over a year ago

Add that criteria in the first part inside query const query = { ... }

Sergio Cano Over a year ago

mmm it is not finding well.. i think something is wrong with my sintax... where should i add the operators $gte and $lt?

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