My mongodb-Basic notes

A summary of MongoDB knowledge points

1.ObjectId 12 bit 4 time stamp +3 machine identification +2 process id+3 random number

Gettimestamp ()

STR ()

2.Map Reduce performs a large amount of work decomposition and then merges the results into the final result.

3.MongoDB Full-Text Search

CREATE INDEX: Db.posts.ensureIndex ({post_text: "text"})

Use full-Text search: Db.posts.find ({$text: {$search: "Runoob"}})

To delete a full-text index:

Db.posts.getIndexes ()

Db.posts.dropIndex ("Post_text_text")

4. You can use the regular

There are three ways to use regular queries:

Db.posts.find ({post_text:{$regex: "Runoob"}})

Db.posts.find ({post_text:/runoob/})

Title:eval ("/" +title+ "/I")//equal to title:{$regex: title, $Option: "$i"}

5. Fixed-size collections

Features:1> insertion speed very fast 2> query output in order of insertion very fast 3> can eliminate the earliest data when inserting the latest data

Usage:1> store log information 2> cache a small number of documents

Created: Db.createcollection ("Cappedlogcollection", {capped:true,size:10000,max:1000}) fixed size fixed number of documents

Judgment: db.cappedLogCollection.isCapped ()

Conversion: Db.runcommand ({"converttocapped": "Posts", size:10000})

Query: Db.cappedLogCollection.find (). Sort ({$natural:-1})

6. Self-increment

MongoDB is not implemented and can be turned into this function

This function realizes the self-increment of the key

function Getnextsequencevalue (sequencename) {

var sequencedocument = db.counters.findAndModify (

{

Query:{_id:sequencename},

Update: {$inc: {sequence_value:1}},

"New": True

});

return sequencedocument.sequence_value;

}

7.GridFS

Store files that exceed 16M

Information description for Files file

Chunk file Splitter 256k/

8.MongoDb relationship 1:1 1:n n:1 n

1-to-many: introduction-Relational embedded relationships

9. References to databases

{

$ref: Collection Name

$ID: The ID of the reference

$DB: Database name, optional parameters

}

Use:

>var user = Db.users.findOne ({"Name": "Tom Benzamin"})

>var Dbref = user.address

>db[dbref. $ref].findone ({"_id":(dbref. $id)})

10. Use of the overlay index

Db.users.ensureIndex ({gender:1,user_name:1})

Db.users.find ({gender: "M"},{user_name:1,_id:0}) is correct

Db.users.find ({gender: "M"},{user_name:1}). Error

11. Query Analysis

Hint () and explain ()

12.MongoDB Atomic operation

Does not support things, but supports operations of some atoms

。。。 For example, $set $unset $inc $push $pushAll $pull $addToSet of $rename $bit

Use of 13.MonogoDB indexes

CREATE INDEX: Db.users.ensureIndex ({"Tags": 1})

Use index: Db.users.find ({tags: "cricket"})

Verify using: Db.users.find ({tags: "cricket"}). Explain ()

Indexed sub-document fields:

Index created: Db.users.ensureIndex ({"address.city": 1, "address.state": 1, "Address.pincode": 1})

Index use: Db.users.find ({"address.city": "Los Angeles"})

Index purpose: Easy to read, disadvantage additional memory overhead, 2.6 increases the length limit for indexed field values.

14. Basic

MongoDB installation and connection slightly

Create DATABASE: Use Runoob

View all databases: Show DBS

Insert data: Db.runoob.insert ({"Name": "Rookie Tutorial"})

Delete Current database: Db.dropdatabase ()

Delete collection: Db.collection.drop ()

Create collection: Db.cretecollection (name,{capped:true, Autoindexid:true, size:6142800, max:10000})

Capped: Whether fixed

AUTOINDEXID: Whether to create an index with _id

Size: Collection Maximum value

Max: Contains the maximum number of documents in the collection

Inserting documents: Db.col.insert (document)

To update a document:

Db.collection.update (

<query>,

<update>,

{

Upsert: <boolean>

Multi: <boolean>

Writeconcern: <document>

}

)

To delete a document:

Db.collection.remove (

<query>,

<justOne>

)

Query document: Db.col.find (). Pretty ()

Operator Description:

Conditional operator: ><>=<= ...

$type: Data type and number correspondence

Limit and Skip $GT optimizations

Sort ()

Aggregate aggregation operations ...

Pipe: The output of the current command as a parameter to the next command

MongoDB replication: Replicas take over the primary node as the primary node without any downtime

Sharding....

Use in MongoDB Java and node. js ....

My mongodb-Basic notes