I'm using mongodb v4.0.3, and this happens both with the shell and in compass.
This only happens with a certain collection. It previously had overriden ids (instead of the default mongodb id, there was a string. I dropped the collection and I recreated it without that).
I have the following structure ("mystructure"), for example:
{
"_id":ObjectId("5bd44eb528d61e3374b5e6ea"),
"custom_field":"data",
}
When I query it without a filter it returns all the docs:
db.mystructure.find({});
When I search for its objectid, it returns properly
db.mystructure.find( {"_id": ObjectId("5bd44eb528d61e3374b5e6ea")} );
But when I try to filter with any field, it doesn't return anything
db.mystructure.find( {"custom_field": "data"} );
At first I thought it would be solved recreating the collection with the automatically generated ids from mongodb but the problem persists. There are no "hidden" spaces in the string or anything like that. The same query in compass isn't working either. Other collections do work. It's on the same db, with the same user.
Why can this be?
Thank you very much.
you should write below code where 62c01e5a763d106152a2e53f is your _id
{_id:ObjectId('62c01e5a763d106152a2e53f')}
I am using PyMongo to insert data (title, description, phone_number ...) into MongoDB. However, when I use mongo client to view the data, it displays the properties in a strange order. Specifically, phone_number property is displayed first, followed by title and then comes description. Is there some way I can force a particular order?
The above question and answer are quite old. Anyhow, if somebody visits this I feel like I should add:
This answer is completely wrong. Actually in Mongo Documents ARE ordered key-value pairs. However when using pymongo it will use python dicts for documents which indeed are not ordered (as of cpython 3.6 python dicts retain order, however this is considered an implementation detail). But this is a limitation of the pymongo driver.
Be aware, that this limitation actually impacts the usability. If you query the db for a subdocument it will only match if the order of the key-values pairs is correct.
Just try the following code yourself:
from pymongo import MongoClient
db = MongoClient().testdb
col = db.testcol
subdoc = {
'field1': 1,
'field2': 2,
'filed3': 3
}
document = {
'subdoc': subdoc
}
col.insert_one(document)
print(col.find({'subdoc': subdoc}).count())
Each time this code gets executed the 'same' document is added to the collection. Thus, each time we run this code snippet the printed value 'should' increase by one. It does not because find only maches subdocuemnts with the correct ordering but python dicts just insert the subdoc in arbitrary order.
see the following answer how to use ordered dict to overcome this: https://stackoverflow.com/a/30787769/4273834
Original answer (2013):
MongoDB documents are BSON objects, unordered dictionaries of key-value pairs. So, you can't rely on or set a specific fields order. The only thing you can operate is which fields to display and which not to, see docs on find's projection argument.
Also see related questions on SO:
MongoDB field order and document position change after update
Can MongoDB and its drivers preserve the ordering of document elements
Ordering fields from find query with projection
Hope that helps.
I have a user collection ,I want to see schema for this collection with data type and other detail,which I want to use in mongoosJs while making Schema.
I found a way on internet ,but it is not providing me full detail of collections-below is code for same
var users= db.users.findOne();
for (var key in users) { print (key) ; }
Is there any way to find it.
You can modify your code as per lines below:-
var col_list = db.users.findOne();
for (var col in col_list) {print (typeof col) }
There is no such thing as a schema in mongo. Documents can differ greatly from each other.
So there can be one document where field username is String and another document where field username is Integer.
You could extract the 'schema' from collection by iterating over all documents and collecting schematic information from all of them and then merging that information. But as far as I know there is no direct way in mongo itself.
Edit: a little googling landed me at variety.js, which seems to do what you need.
From the looks of the syntax for handling mongodb related things in meteor it seems that you always need to know the collection's name to update, insert, remove or anything to the document.
What I am wondering is if it's possible to get the collection's name from the _id field of a document in meteor.
Meaning if you have a document with the _id equal to TNTco3bHzoSFMXKJT. Now knowing the _id of the document you want to find which collection the document is located in. Is this possible through meteor's implementation of mongodb or vanilla mongodb?
As taken from the official docs:
idGeneration String
The method of generating the _id fields of new documents in this collection. Possible values:
'STRING': random strings
'MONGO': random Meteor.Collection.ObjectID values
The default id generation technique is 'STRING'.
Your best option would be to insert records within a pseudo transaction where the second step is to take the id and collection name to feed it into a reference collection. Then, you can do your lookups from that.
It would be pretty costly, though to construct your find's but might be a pattern worthwhile exploring if you are building an app where your users will be creating arbitrary data patterns.
You could accomplish this by doing a findOne on all of the collections:
var collectionById = function(id) {
return _.find(_.keys(this), function(name) {
if (this[name] instanceof Meteor.Collection) {
if (this[name].findOne(id)) {
return true;
}
}
});
};
I tested this on both the client and the server and it seemed to work when run in the global context.
So this is Day 3 of learning Mongo Db. I'm coming from the MySql universe...
A lot of times when I need to write a query for a MySql table I'm unfamiliar with, I would use the "desc" command - basically telling me what fields I should include in my query.
How would I do that for a Mongo db? I know, I know...I'm searching for a schema in a schema-less database. =) But how else would users know what fields to use in their queries?
Am I going at this the wrong way? Obviously I'm trying to use a MySql way of doing things in a Mongo db. What's the Mongo way?
Type the below query in editor / mongoshell
var col_list= db.emp.findOne();
for (var col in col_list) { print (col) ; }
output will give you name of columns in collection :
_id
name
salary
There is no good answer here. Because there is no schema, you can't 'describe' the collection. In many (most?) MongoDb applications, however, the schema is defined by the structure of the object hierarchy used in the writing application (java or c# or whatever), so you may be able to reflect over the object library to get that information. Otherwise there is a bit of trial and error.
This is my day 30 or something like that of playing around with MongoDB. Unfortunately, we have switched back to MySQL after working with MongoDB because of my company's current infrastructure issues. But having implemented the same model on both MongoDB and MySQL, I can clearly see the difference now.
Of course, there is a schema involved when dealing with schema-less databases like MongoDB, but the schema is dictated by the application, not the database. The database will shove in whatever it is given. As long as you know that admins are not secretly logging into Mongo and making changes, and all access to the database is controller through some wrapper, the only place you should look at for the schema is your model classes. For instance, in our Rails application, these are two of the models we have in Mongo,
class Consumer
include MongoMapper::Document
key :name, String
key :phone_number, String
one :address
end
class Address
include MongoMapper::EmbeddedDocument
key :street, String
key :city, String
key :state, String
key :zip, String
key :state, String
key :country, String
end
Now after switching to MySQL, our classes look like this,
class Consumer < ActiveRecord::Base
has_one :address
end
class Address < ActiveRecord::Base
belongs_to :consumer
end
Don't get fooled by the brevity of the classes. In the latter version with MySQL, the fields are being pulled from the database directly. In the former example, the fields are right there in front of our eyes.
With MongoDB, if we had to change a particular model, we simply add, remove, or modify the fields in the class itself and it works right off the bat. We don't have to worry about keeping the database tables/columns in-sync with the class structure. So if you're looking for the schema in MongoDB, look towards your application for answers and not the database.
Essentially I am saying the exactly same thing as #Chris Shain :)
While factually correct, you're all making this too complex. I think the OP just wants to know what his/her data looks like. If that's the case, you can just
db.collectionName.findOne()
This will show one document (aka. record) in the database in a pretty format.
I had this need too, Cavachon. So I created an open source tool called Variety which does exactly this: link
Hopefully you'll find it to be useful. Let me know if you have questions, or any issues using it.
Good luck!
AFAIK, there isn't a way and it is logical for it to be so.
MongoDB being schema-less allows a single collection to have a documents with different fields. So there can't really be a description of a collection, like the description of a table in the relational databases.
Though this is the case, most applications do maintain a schema for their collections and as said by Chris this is enforced by your application.
As such you wouldn't have to worry about first fetching the available keys to make a query. You can just ask MongoDB for any set of keys (i.e the projection part of the query) or query on any set of keys. In both cases if the keys specified exist on a document they are used, otherwise they aren't. You will not get any error.
For instance (On the mongo shell) :
If this is a sample document in your people collection and all documents follow the same schema:
{
name : "My Name"
place : "My Place"
city : "My City"
}
The following are perfectly valid queries :
These two will return the above document :
db.people.find({name : "My Name"})
db.people.find({name : "My Name"}, {name : 1, place :1})
This will not return anything, but will not raise an error either :
db.people.find({first_name : "My Name"})
This will match the above document, but you will have only the default "_id" property on the returned document.
db.people.find({name : "My Name"}, {first_name : 1, location :1})
print('\n--->', Object.getOwnPropertyNames(db.users.findOne())
.toString()
.replace(/,/g, '\n---> ') + '\n');
---> _id
---> firstName
---> lastName
---> email
---> password
---> terms
---> confirmed
---> userAgent
---> createdAt
This is an incomplete solution because it doesn't give you the exact types, but useful for a quick view.
const doc = db.collectionName.findOne();
for (x in doc) {
print(`${x}: ${typeof doc[x]}`)
};
If you're OK with running a Map / Reduce, you can gather all of the possible document fields.
Start with this post.
The only problem here is that you're running a Map / Reduce on which can be resource intensive. Instead, as others have suggested, you'll want to look at the code that writes the actual data.
Just because the database doesn't have a schema doesn't mean that there is no schema. Generally speaking the schema information will be in the code.
I wrote a small mongo shell script that may help you.
https://gist.github.com/hkasera/9386709
Let me know if it helps.
You can use a UI tool mongo compass for mongoDb. This shows all the fields in that collection and also shows the variation of data in it.
If you are using NodeJS and want to get the all the field names using the API request, this code works for me-
let arrayResult = [];
db.findOne().exec(function (err, docs)){
if(err)
//show error
const JSONobj = JSON.parse(JSON.stringify(docs));
for(let key in JSONobj) {
arrayResult.push(key);
}
return callback(null, arrayResult);
}
The arrayResult will give you entire field/ column names
Output-
[
"_id",
"emp_id",
"emp_type",
"emp_status",
"emp_payment"
]
Hope this works for you!
Consider you have collection called people and you want to find the fields and it's data-types. you can use below query
function printSchema(obj) {
for (var key in obj) {
print( key, typeof obj[key]) ;
}
};
var obj = db.people.findOne();
printSchema(obj)
The result of this query will be like below,
you can use Object.keys like in JavaScript
Object.keys(db.movies.findOne())