Questions[mongodb]

I have a problem with this query:

db.estudiantes.find({materias:{$gt:"3.0"}}) 

The intention of this is to find students who have failed at least one subject (the minimum passing grade is 3.0)

The data has this structure:

db.estudiantes.insert({
  id:"1000",
  nombre:"Diego Agreda",
  edad:"15",
  programa:"informatica",
  materias:[{programacion:"5.0",leyes:"2.1",ingles:"4.1"}]
})

When launching the query

 db.estudiantes.find({materias:{$gt:"3.0"}})

It doesn't give me any results. Why does that happen? How can I solve that?

I am starting in Mongodb, and as you know this does not have relaciones, there is no joins tablasetc.

I'm trying to pass a relational diagram to NOSQL. I have the following tables.

users

id

name

messages

idUserFrom

idUserTo

messages

As you can see, the table messageshas as foreign the id of users, how can I create it although there is not in mongo pksand fkshow can I carry out this step.

So far I have created the database and one collectionwith the insertion of the table users.

> use mongodb
switched to db mongodb
> db
mongodb
> db.users.insert({id:"1",name:"Jorge"})
WriteResult({ "nInserted" : 1 })
> show collections
users
> db.users.find().pretty();
{
        "_id" : ObjectId("5c9bbc275a56aa679bb06155"),
        "id" : "1",
        "name" : "Jorge"
}

collectionsHow can I make it look like this messages: This table contains the id of some user, which can be the idFromoridTo

db.messages.find().pretty();



  {
            "_id" : ObjectId("5c9bbc275a56aa679bb06155"),
            "idFrom" : "xxxxxxxxxx",
            "idTo"   : "xxxxxxxxxx",
            "message" : "Hola"
    }

I have in a collection documents like the following:

{
  id: ObjectId(13796844978),
  n_empleado:1,
  geometry:{
     coordinates:[0,1]
  }
}

I'm trying to update the coordinates array and I can't find a way. I am trying, for example, with the following query to add the value 8 to the array:

db.collection.update({n_empleado:1},{$push:{geometry.coordinates:8}})

But an error pops up. The error that the Mongo console gives me is:

E QUERY    [thread1] SyntaxError: missing : after property id @(shell):1:50

I'm also looking for a way to replace the array with another:

db.collection.update({n_empleado:1},{$set:{geometry.coordinates:[4,5]}})

and it also gives an error. The error in this case is:

E QUERY    [thread1] SyntaxError: missing : after property id @(shell):1:49

Any ideas how I can get it?

I'm having a problem getting MongoDB to run on my pc. I have Windows 7 32 bit. I already installed a hotfix that said the page I needed to install and it still won't let me start the service. I attach a screenshot of the windows console with what I get.

Is there a difference between creating an index using the command ensureIndex()and the createIndex()MongoDB command?