Lets say I have a collection "employees" in mongodb.now i want to get the
Schema of that collection using "mongoose".Can I do that? I want to have the
schema object from the collection name.
import mongoose from 'mongoose';
public getMappers(collectionName): Schema {
let schema = mongoose.model(collectionName).schema;
return schema ;
}
is there any way to do this?
Short answer: No.
Let me explain why? NoSQL DBs are known for the flexibility of the unknown data fields. One document can have a different set of fields from another sibling document. Due to this, a tool can not determine all the fields in your schema (and ponder that fields can be added later as well). However, You can get a superset of fields by looking at all the documents in your collections and creating a schema out of it.
Mongo compass has a schema tab where you can analyze and use the collection menu to export schema JSON. See below:
You will still need to do a lot of manipulation to create schema out of this JSON, and this JSON isn't meant for creating schema but to understand the kind of data your collection has. e.g. How many docs have this particular field? How many unique values are there for a particular field(cardinality) etc?
Edit 1: I found that the analyzer runs on a subset of docs only not the full collection. We might miss some fields due to that. Read more here
This question already has an answer here:
Why does mongoose use schema when mongodb's benefit is supposed to be that it's schema-less?
(1 answer)
Closed 5 years ago.
I am a beginner with MongoDB and trying to learn MEAN Stack. So I am using Mongoose as the ORM
I read that MongoDB is a NoSQL database, but while using Mongoose as ORM, I am asked to create a schema first. Why is it so? There shouldn't be a schema ideally as MongoDB is a NoSQL database.
Thanks in advance.
Mongoose is an orm on top of mongodb , if you are using core mongodb you need not create any schema , you can just dump any data you want , but in mongoose you have a schema so that you can i have some basic key value pair for advanced searching and filtering and you can anytime update the schema. Or If you want to go schemaless and dump whatever the response is you can use a schema type like this var someSchema = {data:Object} and drop all your data in this data key and then you can easily extract whatever JSON data is inside your id field.
var mongoose = require('mongoose');
module.exports = mongoose.model('twitter', {
created_at:{
type:Date
},
dump:{
type:Object
}
});
In the above example dump is used to save whatever JSON I get as a response from twitter api and created_at contains only the creating date of tweet , so I have the entire data , but if i want to search tweets of a particular date I can search it using a find query on created_at and this query will be lot faster and here I have a fixed structure and a knowledge about what to expect of a find query each time a run one, So this is one of the benefit of using the mongoose orm i.e I don't lose data but I can maximise my searching ability by creating appropriate keys.
So basically mongoose is an ORM db , it offers you relational db features like creating foreign keys , not strictly foreign keys but you can create something like an id reference to another schema and later populate the field by the id associated parameters when you fetch data using your find query , also a relational schema is easy to manage , what mongoose does is it gives a JSON/BSON based db the power of relational db and you get best of both the world i.e you can easily maintain new keys or you don't need to worry about extracting each and every data from your operation and placing it properly/inserting it , you just need to see that your keys and values match , as well as you have flexibility in update operations while having a schema or table structure.
I'm trying to build routes in my Meteor app. Routing works perfectly fine but getting information from db with route path just doesn't work. I create my page specific routes with this:
FlowRouter.route('/level/:id'...
This route takes me to related template without a problem. Then I want to get some data from database that belong to that page. In my template helpers I get my page's id with this:
var id = FlowRouter.getParam('id');
This gets the ObjectID() but in string format. So I try to find that ObjectID() document in the collection with this:
Levels.findOne({_id: id});
But of course documents doesn't have ObjectIDs in string format (otherwise we wouldn't call it "object"id). Hence, it brings an undefined error. I don't want to deal with creating my own _ids so is there anything I can do about this?
PS: Mongo used to create _ids with plain text. Someting like I would get with _id._str now but all of a sudden, it generates ObjectID(). I don't know why, any ideas?
MongoDB used ObjectIds as _ids by default and Meteor explicitly sets GUID strings by default.
Perhaps you inserted using a meteor shell session in the past and now used a mongo shell/GUI or a meteor mongo prompt to do so, which resulted in ObjectIds being created.
If this happens in a development environment, you could generate the data again.
Otherwise, you could try to generate new _ids for your data using Meteor.uuid().
If you want to use ObjectId as the default for a certain collection, you can specify the idGeneration option to its constructor as 'MONGO'.
If you have the string content of an ObjectId and want to convert it, you can issue
let _id = new Mongo.ObjectID(my23HexCharString);
I have a question on best practises or ideal way how I should store the data in the database. As an example I have a Site that has a Country assigned.
Table Countries: id|name|alpha2
Table Sites: id|countryId|name
Each Site has a reference to the country ID.
I would like to create a new website using Meteor and its mongodb and was wondering how I should store the objects. Do I create a colleciton "countries" and "sites" and use the country _id to as a reference? Then resolve the references using transform?
Looking at SimpleSchema I came up with the following:
Schemas.Country = new SimpleSchema ({
name: {
type: String
},
alpha2: {
type: String,
max: 2
}
});
Schemas.Site = new SimpleSchema({
name: {
type: String,
label: "Site Name"
},
country: {
type: Schemas.Country
}
});
Countries = new Meteor.Collection("countries");
Countries.attachSchema(Schemas.Country);
Sites = new Meteor.Collection("sites");
Sites.attachSchema(Schemas.Site);
I was just wondering how this is then stored in the db. As I have 2 collections but inside the sites collection I do have defined country objects as well. What if a country changes its alpha2 code (very unlikely)?
Also this would continue where I have a collection called "conditions". Each condition will have a Site defined. I could now define the whole Site object into the condition object. What if the Sitename changes? Would I need to manually change it in all condition objects?
This confuses me a bit. I am very thankful for all your thoughts.
The challenge with Meteor is that its tightly bound to Mongo, which is not good to built OLTP app that require normalized DB design. Mongo is good for OLAP kind of apps which fall in WORM (Write Once Read Many) category. I would like to see Meteor supporting OrientDB as they do Mongo.
There can be two approaches:
Normalize the DB as we do in RDBMS and then retrieve data by hitting
data multiple times. Here is a good article explaining this approach - reactive joins in meteor.
Joins in
Meteor
are suggested in future. You can also try Meteor packages - publish
composite or
publish with
relations
Keep data de-normalized at least partially (for 1-N relation you can
embed things in document, for N-N relation you may having separate
collection). For instance, 'Student' can be embedded in 'Class' as
student will never be in more than 1 class, but to relate 'Student'
and 'Subject', they can be in different collections (N-N relation -
student will have more than one subject and each subject will be
taken by more than one student). For fetching N-N relation again you
can use the same approach that is mentioned point above.
I am not able to give you exact code example, but I hope it helps.
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())