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Why does mongoose use schema when mongodb's benefit is supposed to be that it's schema-less?
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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.
Related
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
I have a case where I need to change the default referencing of primary key name id with _id for all the models in a given project I am working.
There is an express.js + mongoose setup which is in production. The data present in the database is directly referred by our users using mobile application. And the code of mobile application is very much aware of reading _id as the key in all the documents it receives in JSON.
Since sails uses waterline which has default key name as id and it maps to _id for mongodb, the underlying database will be used as it is, however on the middleware we are always reading it as id.
I have searched through the web and tried to have default id name as _id in the config/models.js, but the schema creation outputs an error stating _id, _id is used twice.
Production database, Waterline ... I recommend against actually changing your primary keys. Heck, I'd recommend against that kind of monkey-wrench if you were using a much more mature ORM.
Instead, I say, transform the key names in your action. e.g. in an action2, where you just return template variables at the end of a function:
r = await Model.findOne(where);
return {
_id: r.id, // <---- this bit <----
etc: r.etc
}
And then make a JSON structure as your view template.
The save() method seems to replace an entire document/record in my database. If I know the primary key of a document in my database, what is the best way in Grails for me to update a single field on that document without first querying the database using get()?
For instance, I don't like the following code because it executes two queries when all I want to do is to update myField.
def key = "foo"
def doc = MyDomain.get(key) // This is the query I want to eliminate
doc.myField = "bar"
doc.save()
In situations where I know the primary key, I want to simply update a single field, similarly to how Ruby on Rails leverages the ActionModel.update_attribute() method.
Even though my specific database is MongoDB, I think the question is applicable to any database, SQL or NoSQL. If the database supports the ability to update just a single field on one record via one query, using Grails can I avoid the extra get() query to retrieve a full record from the database?
I am a newbie to mongo, I have a collection in my mongodb, To test a feature in my project I need to update database with some random data.I need a script to do that. by identifying the datatype of the field script should fill up the data automatically.
suppose I have the fields in the collection:
id, name, first_name, last_name, current_date, user_income etc.
Since the my questions are as follows:
1. Can we get all field names of a collection with their data types?
2. Can we generate a random value of that data type in mongo shell?
3. how to set the values dynamically to store random data.
I am frequently putting manually to do this.
1. Can we get all field names of a collection with their data types?
mongodb collections are schema-less, which means each document (row in relation database) can have different fields. When you find a document from a collection, you could get its fields names and data types.
2. Can we generate a random value of that data type in mongo shell?
3. how to set the values dynamically to store random data.
mongo shell use JavaScript, you may write a js script and run it with mongo the_js_file.js. So you could generate a random value in the js script.
It's useful to have a look at the mongo JavaScript API documentation and the mongo shell JavaScript Method Reference.
Other script language such as Python can also do that. mongodb has their APIs too.
I am new to mongo db
using i have to delete data from a table like
select from table where id=12 and browser =GC
But I dont know how to perform this in mongo db?
Use remove
db.collectionName.remove({'_id':12,'browser':"GC"})
Can provide more accurate answer if you show your collection and documents .