Shulou(Shulou.com)06/02 Report--

In this issue, the editor will bring you about how to use the array in MongoDB. The article is rich in content and analyzes and narrates it from a professional point of view. I hope you can get something after reading this article.

01 array usage scenario

The inclusion structure of 0101 1Rom N uses an array

0102 single document size limit

02 multiple array operation modes

0201 append array elements with $push

0202 detach array elements using $unwind aggregation

Array is the data structure that best embodies the idea of MongoDB nesting design in MongoDB.

Starting with a PPT of MongoDb community activities, in what scenarios is it appropriate to use arrays?

The inclusion structure of 1Rom N uses an array

For example, if the group in the organizational structure and the inclusion structure of the group member 1veN, you can use the array.

Add: ISODate ("2017-08-23T17:15:56.173+08:00")

"agid": 10, group number

"order":

"user": [

{

"name":

"uid": 1240

"email":

"status": 1

Edit: ISODate ("2017-08-16T00:00:18.685+08:00")

"scope": 1

"desc": "Service staff"

}

{

"name":

"uid": 1442

"email":

"status": 1

Edit: ISODate ("2017-08-16T00:00:18.685+08:00")

"scope": 1

"desc": "Service staff"

}

]

In the above designs, each group is a row in MongoDB, and as the number of members increases, the size of each row increases, so the upper limit of an array element in PPT is small. As long as it is no more than 16m. On the contrary, if we choose this set structure in development, then there should be a pre-judgment about the size of the entire data set and the size of a single collection, or the total amount is controllable and not too large.

A controllable list of article comments, or a work order update reply log, can be saved using an array.

Multiple array operation modes

Manipulating arrays in MongoDb is not as neat and convenient as a relational database, but don't worry, there are ways to do it.

Imagine such a usage scenario, a list of article comments, or a work order update reply log using an array to save, how to add elements to the array?

The following example appends 89 to the scores array:

Db.students.update ({_ id:1}, {$push: {scores:89}})

Use $push with the$each modifier to append multiple values to the array field.

The following example appends each element of [90,92,85] tothescoresarray for the document where thenamefieldequalsjoe:

Db.students.update ({name: "joe"}, {$push: {scores: {$each: [90pence 92jue 85]})

With more flexibility in the use of MongoDb, you can view official documents for more use cases with the help of operator commands

How to query after the element array is complete?

Suppose the following is our document structure

{

"_ id": ObjectId ("591be87de28db61328007ca4")

"name": "Hospital complex"

"status": 1

Create_time: ISODate ("2017-05-17T14:06:53.000+08:00")

Update_time: ISODate ("2017-05-17T14:23:11.000+08:00")

"strategies": [

{

"strategyid": 1495101761

"topic": "cloud"

}

{

"strategyid": 1456101761

"topic": "db"

}

]

}

If we want to query the following specific array elements through the topic condition

{

"strategyid": 1495101761

"topic": "cloud"

}

We need pipeline aggregations and the $unwind operator. The array node of a document is split into individual documents through the $unwind operator, and specific array elements are queried in conjunction with $match.

$mongo=Mongodb::getInstance ()

$ops= [

[

'$unwind'= >' $strategies']

[

'$match'= > [

'strategies.topic'= > $topic

]

[

'$group'= > [

'_ id'= >

['strategies'= >' $strategies.topic']

'strategyid'= > [' $push'= >'$strategies.strategyid']

]]

]

$collection=$mongo- > db- > collection

$data=$collection- > aggregate ($ops)

Return$data ['result']

This is how the array is used in the MongoDB shared by the editor. If you happen to have similar doubts, please refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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