Introduction and practice of MongoDB

This is the 26th day of my participation in Gwen Challenge

preface

What is MongoDB?

MongoDB is an open source database system based on distributed file storage written in C++ language. MongoDB stores data as a document. The data structure consists of key=>value pairs. Belong to no.

What is NoSQL?

NoSQL refers to a non-relational database. Sometimes called Not Only SQL, NoSQL is used for storing very large amounts of data.

MongoDB has a lot of characteristics, here are the main points:

1. First, the programming languages it supports: RUBY, PYTHON, JAVA, C++, PHP, C#, etc.

2. You can set the index of any property

3. Mongo supports rich query expressions

4. Map/ Reduce in Mongodb is mainly used for batch processing and aggregation of data.

Download and install

www.mongodb.com/download-ce…

Management tool

RockMongo is recommended — lightweight and supports multiple languages.

1. Basic Concepts

There are many concepts in mongoDB that are very different from relational databases and need to be understood first.

Database: Multiple databases can be created. The default database is DB.

Collections: Just like tables in a relational database, collections are a combination of documents that can be inserted into different formats and types of data.

For example, insert the following documents into a collection. When a document is inserted, the collection is created.

{"title":"cat"}
{"age":5."name":"miaomiao"} 
{"age":6."name":"haha"."color":"white"}
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Document: a set of key-value data in key-value pair format. Such as:

{"age":5."name":"miaomiao"}
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Fields: Metadata, which can be thought of as data in a document.

Comparison with relational databases:

Second, MongoDB practical operation

Creating a database

use DATABASE_NAME
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If there is a database, it will be switched over, and if there is no database, it will be created automatically.

Viewing all databases

> show dbs
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Create a collection

db.createCollection(name, options)
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• Name: Name of the collection to be created
• Options: Optional parameters that specify memory size and index options

> use test 
switched to db test 
> db.createCollection("animal") 
{ "ok" : 1 }
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Inserted into the document

Db. COLLECTION_NAME. Insert (document) or the COLLECTION_NAME. Save (document)Copy the code

You can create a collection by inserting the document. The collection name is COLLECTION_NAME.

Db.collection.insertone (), which inserts a new document.

>db.col.insert({ "title" : "dog", "age" : 5, "color" : "white", "name" : "wanwan" })
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Important: Key/value pairs in the document are ordered, type – and case-sensitive, and cannot have duplicate keys.

Query the document

The find () method.

db.collection.find(query, projection)
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Projection is a key that needs to be returned. Projection is a key that needs to be returned. Projection is a key that needs to be returned. Some of mongoDB’s operators are needed here.

Correlation operator

Operator used for comparison

$gt – greater than

$lt – less than

$gte– is greater than or equal to

$LTE — less than or equal to

Conditional operator

And (and)

>db.col.find({key1:value1, key2:value2}).pretty()

And (or)

>db.col.find( { $or: [ {key1: value1}, {key2:value2} ] } ).pretty()

The instance

Now you have this document data.

> db.col.find() { “_id” : ObjectId(“56066542ade2f21f36b0313a”), “title” : “dog”, “age” : 5, “color” : “white”, “name” : “wanwan” }

{ “_id” : ObjectId(“56066542ade2f223420313a”), “title” : “cat”, “age” : 7, “color” : “white”, “name” : “miaomiao” }

{ “_id” : ObjectId(“56242342342f21f36b0313a”), “title” : “pig”, “age” : 2, “color” : “black”, “name” : “hoho” }

Below is the query document statement covering greater than, and or.

>db.col.find({"age": {$gt:5}, $or: [{"color": "white"},{"title": "pig"}]}).pretty() 
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Query result:

{

"_id" : ObjectId("56066542ade2f223420313a"), 

"title" : "cat"."age" : "Seven"."color" : "white"."name" : "miaomiao" 

}
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The sorting

Use the sort() method to specify the sort of parameters, 1 for ascending and -1 for descending.

>db.COLLECTION_NAME.find().sort({KEY:1})
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Descending by age for documents in the above collection.

>db.col.find({},{"title":1,_id:0}).sort({"age":- 1}) 
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Results:

{ "title" : "cat" } 
{ "title" : "dog" } 
{ "title" : "pig" } 
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