MongoDB Basics

MongoDB Basics.md

Welcome to MongoDB Basics by Roberto Jacobo

Importing and Exporting Data

As we know MongoDB handle the data in JSON and BSON (Binary JSON) but, first we need to decide how we are going to handle de data.

JSON

mongoimport
mongoexport

BSON

mongorestore
mongodump

To connect to your Atlas cluster. URI: Uniform Resourse Identifier mongodb+srv://user:password@clusterURI.mongodb.net/database srv - establishes a secure connection

Export data

mongodump --uri "<Atlas Cluster URI>"

Exports data in BSON

mongoexport --uri "< Atlas Cluster URI >"
		    --collection=<collection name>
			--out=<filename>.json  

Exports data in JSON

Import data

mongorestore --uri "< Atlas Cluster URI >"
		     --drop dump

Imports data in BSON dump

mongoimport --uri "<Atlas Cluster URI>"
            --drop=<filename>.json

Imports data in JSON

Find()

with the mongo shell we are using this command and string to connect and find the DB information.

mongo "mongodb+srv://sandbox.kgcwj.mongodb.net/myFirstDatabase" 

you can add the username at the end like:

"mongodb+srv://sandbox.kgcwj.mongodb.net/myFirstDatabase"  --username m001-student

to see the databases available

show dbs

And you'll see something like in the command line:

admin               0.000GB
local               4.032GB
sample_airbnb       0.051GB
sample_analytics    0.009GB
sample_geospatial   0.001GB
sample_mflix        0.041GB
sample_restaurants  0.006GB
sample_supplies     0.001GB
sample_training     0.042GB
sample_weatherdata  0.002GB

example from the mongo's database

command	action
show dbs	Show all the db's in the project
use < database name >	Get into the db
show collections	Show all the collectionts in the database
db.< db >.find({"< field >":"< value >"})	Find all documents that match the indicated field and value

If there are too much collectiont in return of .find() we can tap it to get more collections in the command prompt

Inserting New Documents

must know

"_id" unique identifier for a document in a collection "_id" is required in every MongoDB Document ObjectId() is the default value for the "_id" field unless otherwise specified if we try to insert a document that already exist in the collection with the same _id then we get a duplicate key error

db.inspections.findOne()

finds a random document in a collection

we can insert documents with the followind command example

db.collection.insert({<doc:1>})

and we can insert many collections like this:

db.collection.insert([{<doc:1>}.{<doc:2>}])

using an array

The behavior of .insert() is to insert the documents following the order indicated in the array but we can insert unordered using {"ordered": false} like this:

db.collection.insert([{<doc:1>}.{<doc:2>}], {"ordered": false})

if we try to insert many documents in a collection and there is an _id field that repeats mongo insert all the documents indicated before that error. If it's located in the second document indicated there only will be one document inserted.

db.collection.insert([{ "_id": 1, "pet": "cat" }, { "_id": 1, "pet": "dog" }, { "_id": 3, "pet": "snake" }], {"ordered": true})

Here only be the first document inserted and if ordered is setted to false only one of the documents that has "_id": 1 and "_id": 3 would be inserted.