Kuidas MongoDB-ga alustada 10 minutiga

MongoDB on rikkalik dokumendile orienteeritud NoSQL-i andmebaas.

Kui olete NoSQL-i täielik algaja, soovitan teil kiiresti vaadata minu varem avaldatud NoSQL-i artiklit.

Täna tahtsin jagada mõningaid põhilisi asju MongoDB käskude kohta, näiteks päringute esitamine, andmete filtreerimine, kustutamine, värskendamine ja nii edasi.

Okei, piisavalt juttu, asume tööle!

Konfiguratsioon?

MongoDB-ga töötamiseks peate kõigepealt installima MongoDB oma arvutisse. Selleks külastage ametlikku allalaadimiskeskust ja laadige alla oma operatsioonisüsteemi versioon. Siin olen kasutanud Windowsi.

Pärast MongoDB kogukonnaserveri seadistuste allalaadimist läbite installimisprotsessi "järgmine pärast järgmist". Kui olete valmis, minge C-draivi juurde, kuhu olete MongoDB installinud. Minge programmifailide juurde ja valige kataloog MongoDB.

C: -> Program Files -> MongoDB -> Server -> 4.0(version) -> bin

Prügikasti kataloogist leiate huvitava paari käivitatavaid faile.

  • mongood
  • mongo

Räägime neist kahest failist.

mongod tähistab “Mongo Daemon”. mongood on taustprotsess, mida kasutab MongoDB. Mongodi peamine eesmärk on kõigi MongoDB serveri ülesannete haldamine. Näiteks päringute vastuvõtmine, kliendile vastamine ja mäluhaldus.

mongo on käsurea kest, mis saab suhelda kliendiga (näiteks süsteemiadministraatorite ja arendajatega).

Vaatame nüüd, kuidas saaksime selle serveri tööle panna. Selleks Windowsis peate kõigepealt oma C-draivi looma paar kataloogi. Avage oma C-draivi käsuviip ja tehke järgmist:

C:\> mkdir data/dbC:\> cd dataC:\> mkdir db

Nende kataloogide eesmärk on, et MongoDB nõuab kõigi andmete salvestamiseks kausta. MongoDB vaikekataloogide /data/dbasukoht on kettal. Seetõttu on vaja, et pakuksime selliseid katalooge.

Kui käivitate MongoDB serveri ilma nende kataloogideta, näete tõenäoliselt järgmist viga:

Pärast nende kahe faili loomist minge uuesti mongodbi kataloogis olevasse prügikasti ja avage oma kest selle sees. Käivitage järgmine käsk:

mongod

Voilà! Nüüd on meie MongoDB server töökorras! ?

Selle serveriga töötamiseks vajame vahendajat. Niisiis avage sidumiskaustas veel üks käsuaken ja käivitage järgmine käsk:

mongo

Pärast selle käsu käivitamist navigeerige shellini, mille käskisime mongodi (mis on meie server). Lõpus näete teadet „ühendus on vastu võetud”. See tähendab, et meie installimine ja seadistamine on edukas!

Lihtsalt jookse mongo kest:

db

Keskkonnamuutujate seadistamine

Aja kokkuhoiuks saate seadistada keskkonnamuutujad. Windowsis tehakse seda järgmiste menüüde järgi:

Advanced System Settings -> Environment Variables -> Path(Under System Variables) -> Edit

Kopeerige lihtsalt meie prügikasti tee ja vajutage OK! Minu puhul on see niiC:\Program Files\MongoDB\Server\4.0\bin

Nüüd on kõik valmis!

Töö MongoDB-ga

MongoDB serveriga nagu MongoDB Compass, Studio 3T ja nii edasi töötamiseks on hulk GUI-sid (graafiline kasutajaliides).

Need pakuvad graafilist liidest, nii et saate hõlpsalt töötada oma andmebaasiga ja täita päringuid, selle asemel, et kasutada shellit ja sisestada päringuid käsitsi.

Kuid selles artiklis kasutame oma töö tegemiseks käsuviiba.

Nüüd on meil aeg sukelduda MongoDB käskudesse, mis aitavad teil oma tulevastes projektides kasutada.

  1. Avage käsuviip ja tippige mongodMongoDB serveri käivitamiseks.

2. Avage teine ​​kest ja tippige mongoühenduse loomiseks MongoDB andmebaasiserveriga.

1. Praeguse andmebaasi leidmine, kus olete

db

See käsk näitab praegust andmebaasi, milles olete. See teston vaikimisi algne andmebaas.

2. Andmebaaside loetlemine

show databases

Praegu on mul neli andmebaasi. Need on: CrudDB, admin, configja local.

3. Minge kindlasse andmebaasi

use 

Here I’ve moved to the local database. You can check this if you try the command dbto print out the current database name.

4. Creating a Database

With RDBMS (Relational Database Management Systems) we have Databases, Tables, Rows and Columns.

But in NoSQL databases, such as MongoDB, data is stored in BSON format (a binary version of JSON). They are stored in structures called “collections”.

In SQL databases, these are similar to Tables.

Alright, let’s talk about how we create a database in the mongo shell.

use 

Wait, we had this command before! Why am I using it again?!

In MongoDB server, if your database is present already, using that command will navigate into your database.

But if the database is not present already, then MongoDB server is going to create the database for you. Then, it will navigate into it.

After creating a new database, running the show database command will not show your newly created database. This is because, until it has any data (documents) in it, it is not going to show in your db list.

5. Creating a Collection

Navigate into your newly created database with the usecommand.

Actually, there are two ways to create a collection. Let’s see both.

One way is to insert data into the collection:

db.myCollection.insert({"name": "john", "age" : 22, "location": "colombo"})

This is going to create your collection myCollectioneven if the collection does not exist. Then it will insert a document with nameand age. These are non-capped collections.

The second way is shown below:

2.1 Creating a Non-Capped Collection

db.createCollection("myCollection")

2.2 Creating a Capped Collection

db.createCollection("mySecondCollection", {capped : true, size : 2, max : 2})

In this way, you’re going to create a collection without inserting data.

A “capped collection” has a maximum document count that prevents overflowing documents.

In this example, I have enabled capping, by setting its value to true.

The size : 2 means a limit of two megabytes, and max: 2 sets the maximum number of documents to two.

Now if you try to insert more than two documents to mySecondCollection and use the find command (which we will talk about soon), you’ll only see the most recently inserted documents. Keep in mind this doesn’t mean that the very first document has been deleted — it is just not showing.

6. Inserting Data

We can insert data to a new collection, or to a collection that has been created before.

There are three methods of inserting data.

  1. insertOne() is used to insert a single document only.
  2. insertMany() is used to insert more than one document.
  3. insert() is used to insert documents as many as you want.

Below are some examples:

  • insertOne()
db.myCollection.insertOne( { "name": "navindu", "age": 22 } )
  • insertMany()
db.myCollection.insertMany([ { "name": "navindu", "age": 22 }, { "name": "kavindu", "age": 20 }, { "name": "john doe", "age": 25, "location": "colombo" } ])

The insert() method is similar to the insertMany() method.

Also, notice we have inserted a new property called locationon the document for John Doe. So if youusefind, then you’ll see only forjohn doe the locationproperty is attached.

This can be an advantage when it comes to NoSQL databases such as MongoDB. It allows for scalability.

7. Querying Data

Here’s how you can query all data from a collection:

db.myCollection.find()

If you want to see this data in a cleaner, way just add .pretty()to the end of it. This will display document in pretty-printed JSON format.

db.myCollection.find().pretty()

Wait...In these examples did you just notice something like _id? How did that get there?

Well, whenever you insert a document, MongoDB automatically adds an _id field which uniquely identifies each document. If you do not want it to display, just simply run the following command

db.myCollection.find({}, _id: 0).pretty()

Next, we’ll look at filtering data.

If you want to display some specific document, you could specify a single detail of the document which you want to be displayed.

db.myCollection.find( { name: "john" } )

Let’s say you want only to display people whose age is less than 25. You can use $lt to filter for this.

db.myCollection.find( { age : {$lt : 25} } )

Similarly, $gt stands for greater than, $lte is “less than or equal to”, $gte is “greater than or equal to” and $ne is “not equal”.

8. Updating documents

Let’s say you want to update someone’s address or age, how you could do it? Well, see the next example:

db.myCollection.update({age : 20}, {$set: {age: 23}})

The first argument is the field of which document you want to update. Here, I specify age for the simplicity. In production environment, you could use something like the _id field.

It is always better to use something like _id to update a unique row. This is because multiple fields can have same age and name. Therefore, if you update a single row, it will affect all rows which have same name and age.

If you update a document this way with a new property, let’s say location for example, the document will be updated with the new attribute. And if you do a find, then the result will be:

If you need to remove a property from a single document, you could do something like this (let’s say you want ageto be gone):

db.myCollection.update({name: "navindu"}, {$unset: age});

9. Removing a document

As I have mentioned earlier, when you update or delete a document, you just need specify the _id not just name, age, location.

db.myCollection.remove({name: "navindu"});

10. Removing a collection

db.myCollection.remove({});

Note, this is not equal to the drop() method. The difference is drop() is used to remove all the documents inside a collection, but the remove() method is used to delete all the documents along with the collection itself.

Logical Operators

MongoDB provides logical operators. The picture below summarizes the different types of logical operators.

Let’s say you want to display people whose age is less than 25, and also whose location is Colombo. What we could do?

We can use the $andoperator!

db.myCollection.find({$and:[{age : {$lt : 25}}, {location: "colombo"}]});

Last but not least, let’s talk aboutaggregation.

Aggregation

A quick reminder on what we learned about aggregation functions in SQL databases:

Lihtsamalt öeldes grupeerib liitmine mitme dokumendi väärtused ja võtab need mingil viisil kokku.

Kujutage ette, kui meil oleks recordBookkollektsioonis mees- ja naisüliõpilasi ning me sooviksime, et igaüks neist kokku arvestaks. Meeste ja naiste summa saamiseks võiksime kasutada $groupkoondfunktsiooni.

db.recordBook.aggregate([ { $group : {_id : "$gender", result: {$sum: 1}} } ]);

Pakkimine

Niisiis, oleme arutanud MongoDB põhitõdesid, mida teil võib rakenduse loomiseks tulevikus vaja minna. Loodan, et teile meeldis see artikkel - aitäh lugemast!

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Link minu eelmisele artiklile: NoSQL