I have a document that has an id of another document from a different collection embedded in it.
My desired result is to return (I'm using python and pymongo) the all the fields of the first collection, and all of the friends from the document that was embedded.
I understand mongo doesn't do joins and I understand I'll need to make two queries. I also don't want to duplicate my data.
My question is how to piece the two queries together in python/pymongo so I have one results with all the fields from both documents in it.
Here is what my data looks like:
db.employees
{_id: ObjectId("4d85c7039ab0fd70a117d733"), name: 'Joe Smith', title: 'junior',
manager: ObjectId("4d85c7039ab0fd70a117d730") }
db.managers
{_id: ObjectId("ObjectId("4d85c7039ab0fd70a117d730"), name: 'Jane Doe', title: 'senior manager'}
desired result
x = {_id: ObjectId("4d85c7039ab0fd70a117d733"), name: 'Joe Smith', title: 'junior',
manager: 'Jane Doe' }
Your basically doing something that Mongo does not support out of the box and would actually be more painful than using the two records separately.
Basically (in pseudo/JS code since I am not a Python programmer):
var emp = db.employees.find({ name: 'Joe Smith' });
var mang = db.managers.find({ _id: emp._id });
And there you have it you have the two records separately. You cannot chain as #slownage shows and get a merged result, or any result infact since MongoDB, from one qauery, will actually return a dictionary not the value of the field even when you specify only one field to return.
So this is really the only solution, to get the the two separately and then work on them.
Edit
You could use a DBRef here but it is pretty much the same as doing it this way, only difference is that it is a helper to put it into your own model instead of doing it youself.
If it works it should be something like:
db.managers.find({
'_id' => db->employees->find({ ('_id' : 1),
('_id': ObjectId("4d85c7039ab0fd70a117d733") }))
})
updated
Related
I made a python script that reads a file and creates a new mongoDB collection.
The collection is as follows, when I print one document of the collection in python:
{'_id': '5b5b0a55ca902423007413b9',
'employee': 'John Doe',
'schedule': [{'date': '08/11/2018', 'project': 'Drawing'},
...
{'date': '05/06/2018', 'project': 'Teaching'}
]
}
I made a collection in meteor using this code:
Planning = new Meteor.Collection("Planning");
Planning is also the name I gave the collection in python.
Now when I run this code in Meteor (server side):
Meteor.methods({
getFullPlanning: function(){
var one = Planning.find({ employee: 'John Doe'});
console.log(one.employee);
}
});
This piece of code logs undefined, but there is an employee with that name in my collection. What am I doing wrong in Meteor?
But this does work:
Planning.find().count() // = 53 which is correct!
According to the Meteor docs:
find returns a cursor. It does not immediately access the database or return documents. Cursors provide fetch to return all matching documents, map and forEach to iterate over all matching documents, and observe and observeChanges to register callbacks when the set of matching documents changes.
Your variable, one, is a cursor, and not the document. If you're only looking for a single document, you can call Planning.findOne({ employee: 'John Doe' }) which will return a single document, or undefined if no matches were found. You can also call Planning.find({ employee: 'John Doe' }).fetch().
Although I think it is a general question, I could not find a solution that matches my needs.
I have 2 Mongo collections. The 'users' collection and the second one 'dbInfos'.
Now, I have a template called 'Infos' and want the already existing fields in the Mongo collections to be presented to the user in input fields in case there is data in the collection. When no data is provided in the database yet, it should be empty.
So here is my code, which works fine until I want to capture the fields from the second collection.
Template.Infos.onRendered(function() {
$('#txtName').val(Meteor.user().profile.name);
$('#txtEmail').val(Meteor.user().emails[0].address);
});
These 2 work great.
But I don´t know how to query the infos from the collection 'dbInfos', which is not the 'users' collection. Obviously Meteor.user().country does not work, because it is not in the 'users' collection. Maybe a find({}) query? However, I don´t know how to write it.
$('#txtCountry').val( ***query function***);
Regarding the structure of 'dbInfos': Every object has an _id which is equal to the userId plus more fields like country, city etc...
{
"_id": "12345",
"country": "countryX",
"city": "cityY"
}
Additionally, how can I guarantee that nothing is presented, when the field in the collection is empty? Or is this automatic, because it will just return an empty field?
Edit
I now tried this:
dbInfos.find({},{'country': 1, '_id': 0})
I think this is the correct syntax to retrieve the country field and suppress the output of the _id field. But I only get [object Object] as a return.
you're missing the idea of a foreign key. each item in a collection needs a unique key, assigned by mongo (usually). so the key of your country info being the same as the userId is not correct, but you're close. instead, you can reference the userId like this:
{
"_id": "abc123",
"userId": "12345",
"country": "countryX",
"city": "cityY"
}
here, "abc123" is unique to that collection and assigned by mongo, and "12345" is the _id of some record in Meteor.users.
so you can find it like this (this would be on the client, and you would have already subscribed to DBInfos collection):
let userId = Meteor.userId();
let matchingInfos = DBInfos.find({userId: userId});
the first userId is the name of the field in the collection, the second is the local variable that came from the logged in user.
update:
ok, i think i see where you're getting tripped it. there's a difference between find() and findOne().
find() returns a cursor, and that might be where you're getting your [object object]. findOne() returns an actual object.
for both, the first argument is a filter, and the second argument is an options field. e.g.
let cursor = DBInfos.find({
userId: Meteor.userId()
},
{
fields: {
country: 1
}
});
this is going to:
find all records that belong to the logged in user
make only the country and _id fields available
make that data available in the form of a cursor
the cursor allows you to iterate over the results, but it is not a JSON object of your results. a cursor is handy if you want to use "{{#each}}" in the HTML, for example.
if you simply change the find() to a findOne():
let result = DBInfos.findOne({ /** and the rest **/
... now you actually have a JSON result object.
you can also do a combination of find/fetch, which works like a findOne():
let result = DBInfos.find({
userId: Meteor.userId()
},
{
fields: {
country: 1
}
}).fetch();
with that result, you can now get country:
let country = result.country;
btw, you don't need to use the options to get country. i've been assuming all this code is on the client (might be a bad assumption). so this will work to get the country as well:
let result = DBInfos.findOne({userId: Meteor.userId()});
let country = result.country;
what's going on here? it's just like above, but the result JSON might have more fields in it than just country and _id. (it depends on what was published).
i'll typically use the options field when doing a find() on the server, to limit what's being published to the client. on the client, if you just need to grab the country field, you don't really need to specify the options in that way.
in that options, you can also do things like sort the results. that can be handy on the client when you're going to iterate on a cursor and you want the results displayed in a certain order.
does all that make sense? is that what was tripping you up?
I want the latest document in the query. Below I'm getting those documents whose name is coming from the variable 'personalFullName, then sorting them by a field called 'RecordID' (this field has higher numbers as later date entries), then grab the last one. I want the latest (the one with the largest RecordID number) entry in this query:
Programs.find({ FullName: personalFullName }, { sort: { RecordID: 1 }, limit: 1}).fetch().pop();
I'm getting an error that it's exceeding the call stack size.
If you are comfortable using the meteorhacks:aggregate package then you could always publish the item(s) you want using the mongo aggregate pipeline, perhaps something like this (code is coffeescript):
Meteor.publish 'latestPrograms', (personalFullName)->
return unless personalFullName?
check personalFullName, String
pipeline = [
{$match:{'Fullname': personalFullName}}
{$sort: {'RecordID': 1}}
{$group:{'_id':{Fullname: '$Fullname'}, RecordID:{$last:'$RecordID'}}}
{$limit:1}
]
#added 'latestPrograms', Random.id(), item for item in programs.aggregate pipeline
#ready()
You can then grab the data by subscribing to the latestPrograms pseudo collection. Here is an example using a iron router route:
Router.route '/home',
name: 'home'
template:'homepage'
waitOn:->
Meteor.subscribe 'latestPrograms', personalFullName
data:->
{latestPrograms: latestPrograms.find()}
I have a number of associated records such as below.
Parent records
{
_id:234,
title: "title1",
name: "name1",
association:"assoc1"
},
Child record
{
_id:21,
title: "child title",
name: "child name1",
},
I want to store such records into MongoDb. Can anyone help?
Regards.
Even MongoDB doesn't support joins, you can organize data in several different ways:
1) First of all, you can inline(or embed) related documents. This case is useful, if you have some hierarchy of document, e.g. post and comments. In this case you can like so:
{
_id: <post_id>,
title: 'asdf',
text: 'asdf asdf',
comments: [
{<comment #1>},
{<comment #2>},
...
]
}
In this case, all related data will be in the save document. You can fetch it by one query, but pushing new comments to post cause moving this document on disk, frequent updates will increase disk load and space usage.
2) referencing is other technique you can use: in each document, you can put special field that contains _id of parent/related object:
{
_id: 1,
type: 'post',
title: 'asdf',
text: 'asdf asdf'
},
{
_id:2
type: 'comment',
text: 'yep!',
parent_id: 1
}
In this case you store posts and comments in same collection, therefor you have to store additional field type. MongoDB doesn't support constraints or any other way to check data constancy. This means that if you delete post with _id=1, comments with _id=2 store broken link in parent_id.
You can separate posts from comments in different collections or even databases by using database references, see your driver documentation for more details.
Both solutions can store tree-structured date, but in different way.
I'm new with MongoDB. I have a design question, about performance of MongoDB. Lets say I have the class Movies with two properties, Name and Director. Also I want to tag this Movie Class. Is better to add a new propertie of strings[] to this class, or to create a new class MovieTags? I know I will query this tags a lot because I will use an autocomplete on the UI. For this autocomplete function I only need the tags, not the Movie object.
What option is better? add a propertie of strings[] or reference to a collection of MovieTags? Thinking in performance... of course in both cases the indexing will be done.
Should I use a MapReduce? To only select the tags, for the autocomplete function if I use an embebed string[] object? How?
Thanks!
I'd probably go with a schema like this, which stores the tags in a string array field:
db.movies.insert({
name: "The Godfather",
director: "Francis Ford Coppola",
tags: [ "mafia", "wedding", "violence" ]
})
db.movies.insert({
name: "Pulp Fiction",
director: "Quentin Tarantino",
tags: [ "briefcase", "violence", "gangster" ]
})
db.movies.insert({
name: "Inception",
director: "Christopher Nolan",
tags: [ "dream", "thief", "subconscious" ]
})
You wouldn't need map-reduce for this type of query. By embedding the tags inside the the movie document you can take advantage of MongoDB's multikey feature, and find movies with a given tag using single find() query like this:
db.movies.find( { tags: "dream" } )
And like you said, it's also worth adding an index to the multikey array to improve query performance:
db.movies.ensureIndex( { tags: 1 } )
You can always filter the fields that are returned as part of the query result.
The link to the docs that details how to do so is http://docs.mongodb.org/manual/tutorial/query-documents/#Querying-FieldSelection
This will let you filter out parts of the movie object that you re not interested in.