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This article mainly introduces what the Query operations commonly used in MongoDB are, which are very detailed and have a certain reference value. Friends who are interested must finish reading them!

The content of this article is about the introduction of common Query operations of MongoDB (with code), there is a certain reference value, friends in need can refer to, hope to help you.

The visualization tool used is Studio 3T, official website-- > https://studio3t.com/

Version number: MongoDB shell version v3.4.2

How to use: https://blog.csdn.net/weixin_...

What to watch: focus on the operator.

How to find: press ctrl+F to enter keywords to find on this page

1. Commonly used Query

For ease of operation, delete all documents before inserting the original data (please be careful in the project! ):

Db.getCollection ("inventory") .deleteMany ({})

0. View all documents

Db.getCollection ("inventory") .find ({})

1. Object lookup

1.1. Original data

Db.inventory.insertMany ([{item: "journal", qty: 25, size: {h: 14, w: 21, uom: "cm"}, status: "A"}, {item: "notebook", qty: 50, size: {h: 8.5, w: 11, uom: "in"}, status: "A"}, {item: "paper", qty: 100, size: {h: 8.5, w: 11 Uom: "in"}, status: "D"}, {item: "planner", qty: 75, size: {h: 22.85, w: 30, uom: "cm"}, status: "D"}, {item: "postcard", qty: 45, size: {h: 10, w: 15.25, uom: "cm"}, status: "A"}])

1.2.Look up documents where size.h equals 14pr size.w equals 21m cm.

Db.inventory.find ({size: {h: 14, w: 21, uom: "cm"}})

1.3.Lookup documents whose size.uom equals in

Db.inventory.find ({"size.uom": "in"})

Note: be sure to put quotation marks when looking for a single object attribute!

1.4. Find and return the specified field in the object

Db.inventory.find ({status: "A"}, {item: 1, status: 1, "size.uom": 1})

1.5. Find and filter the specified fields in the object

Db.inventory.find ({status: "A"}, {"size.uom": 0})

2. Array lookup

2.1. Original data

Db.inventory.insertMany ([{item: "journal", qty: 25, tags: ["blank", "red"], dim_cm: [14,21]}, {item: "notebook", qty: 50, tags: ["red", "blank"], dim_cm: [14,21]}, {item: "paper", qty: 100, tags: ["red", "blank", "plain"], dim_cm: [14 21]}, {item: "planner", qty: 75, tags: ["blank", "red"], dim_cm: [22.85,30]}, {item: "postcard", qty: 45, tags: ["blue"], dim_cm: [10,15.25]}])

2.2.Lookup the tags= ["red", "blank"] documentation

Db.inventory.find ({tags: ["red", "blank"]})

Note: tags: ["red", "blank", "plain"] is not included

2.3.Lookup tags documents that contain red

Db.inventory.find ({tags: "red"})

Note: you cannot write db.inventory.find ({tags: ["red"]}) in this way, which means to find a document where tags is red.

3. Lookup of objects contained in the array

3.1. Original data

Db.inventory.insertMany ([{item: "journal", instock: [{warehouse: "A", qty: 5}, {warehouse: "C", qty: 15})}, {item: "notebook", instock: [{warehouse: "C", qty: 5}]}, {item: "paper", instock: [{warehouse: "A", qty: 60}, {warehouse: "B", qty: 15}]}} {item: "planner", instock: [{warehouse: "A", qty: 40}, {warehouse: "B", qty: 5}]}, {item: "postcard", instock: [{warehouse: "B", qty: 15}, {warehouse: "C", qty: 35}]}])

3.2. Find an object in the array that meets the condition (not included). As long as one object in the array meets the condition, the entire array is returned.

Db.inventory.find ({"instock": {warehouse: "A", qty: 5}})

Strictly follow the order of the fields. If you change the order of the fields, you will not find them, as follows:

Db.inventory.find ({"instock": {qty: 5, warehouse: "A"}})

Find the element object in the array, with the qty=5 of an element object, or the warehouse=An of that object (or other element objects)

Db.inventory.find ({"instock.qty": 5, "instock.warehouse": "A"})

3.4. Find the object in the array and return a property of the object

Db.inventory.find ({status: "A"}, {item: 1, status: 1, "instock.qty": 1})

4. General search

4.1. Original data

Db.inventory.insertMany ([{item: "journal", status: "A", size: {h: 14, w: 21, uom: "cm"}, instock: [{warehouse: "A", qty: 5}]}, {item: "notebook", status: "A", size: {h: 8.5,w: 11, uom: "in"}, instock: [{warehouse: "C", qty: 5}]}} {item: "paper", status: "D", size: {h: 8.5,11, uom: "in"}, instock: [{warehouse: "A", qty: 60}]}, {item: "planner", status: "D", size: {h: 22.85,w: 30, uom: "cm"}, instock: [{warehouse: "A", qty: 40}]}, {item: "postcard" Status: "A", size: {h: 10, w: 15.25, uom: "cm"}, instock: [{warehouse: "B", qty: 15}, {warehouse: "C", qty: 35}]])

4.2. Query and return the specified field

Under the condition of status=A, return the _ id,item,status field

Db.inventory.find ({status: "A"}, {item: 1, status: 1})

Results:

{"_ id": ObjectId ("5c91cd53e98d5972748780e1"), "item": "journal", "status": "A"} /-{"_ id": ObjectId ("5c91cd53e98d5972748780e2"), "item": "notebook" "status": "A"} / /-{"_ id": ObjectId ("5c91cd53e98d5972748780e5"), "item": "postcard", "status": "A"}

4.3. as can be seen from 4.2, _ id is carried automatically and can be removed, as follows

Query without (removing) id:

Db.inventory.find ({status: "A"}, {item: 1, status: 1, _ id: 0})

Note: except that id can filter out and retain other fields, other fields cannot write 1 at the same time.

Such as:

Db.inventory.find ({status: "A"}, {item: 1, status: 0})

Will report an error.

4.4. Exclude specific fields and return to other fields

Db.inventory.find ({status: "A"}, {status: 0, instock: 0})

5. Find null or keys that do not exist

5.1. Original data

Db.inventory.insertMany ([{_ id: 1, item: null}, {_ id: 2}])

5.2. find documents whose item is null, or documents that do not contain item

Db.inventory.find ({item: null})

II. Operators

1. $lt less than is less than

1.1. Original data

Db.inventory.insertMany ([{item: "journal", qty: 25, size: {h: 14, w: 21, uom: "cm"}, status: "A"}, {item: "notebook", qty: 50, size: {h: 8.5, w: 11, uom: "in"}, status: "A"}, {item: "paper", qty: 100, size: {h: 8.5, w: 11 Uom: "in"}, status: "D"}, {item: "planner", qty: 75, size: {h: 22.85, w: 30, uom: "cm"}, status: "D"}, {item: "postcard", qty: 45, size: {h: 10, w: 15.25, uom: "cm"}, status: "A"}])

1.2.Lookup the collection of documents with "size.h" less than 15

Db.inventory.find ({"size.h": {$lt: 15}})

1.3.The lt is used in conjunction with AND

Find documents where size.h is less than 15 and size.uom is in and status is D.

Db.inventory.find ({"size.h": {$lt: 15}, "size.uom": "in", status: "D"})

2. $lte less than equal is less than or equal to

2.1. Original data

Db.inventory.insertMany ([{item: "journal", instock: [{warehouse: "A", qty: 5}, {warehouse: "C", qty: 15})}, {item: "notebook", instock: [{warehouse: "C", qty: 5}]}, {item: "paper", instock: [{warehouse: "A", qty: 60}, {warehouse: "B", qty: 15}]}} {item: "planner", instock: [{warehouse: "A", qty: 40}, {warehouse: "B", qty: 5}]}, {item: "postcard", instock: [{warehouse: "B", qty: 15}, {warehouse: "C", qty: 35}]}])

2.2.Lookup documents whose instock.qty is less than or equal to 20, and return the entire array as long as one object in the array meets the criteria

Db.inventory.find ({'instock.qty': {$lte: 20}})

3. $gt greater than is greater than

3.1. Original data

Db.inventory.insertMany ([{item: "journal", qty: 25, tags: ["blank", "red"], dim_cm: [14,21]}, {item: "notebook", qty: 50, tags: ["red", "blank"], dim_cm: [14,21]}, {item: "paper", qty: 100, tags: ["red", "blank", "plain"], dim_cm: [14 21]}, {item: "planner", qty: 75, tags: ["blank", "red"], dim_cm: [22.85,30]}, {item: "postcard", qty: 45, tags: ["blue"], dim_cm: [10,15.25]}])

3.2.Lookup documents with dim_cm greater than 25

Db.inventory.find ({dim_cm: {$gt: 25}})

Note: as long as an array containing elements greater than 25 is eligible

Find documents whose dim_cm is greater than 15, or less than 20, or both greater than 15 and less than 20

Db.inventory.find ({dim_cm: {$gt: 15, $lt: 20}})

3.4. find documents whose dim_cm is both greater than 22 and less than 30 (to determine whether an element of the array is greater than 22 and less than 30, rather than all the elements of the array)

Db.inventory.find ({dim_cm: {$elemMatch: {$gt: 22, $lt: 30})

3.5. Find based on array location

Find documents whose second element of dim_cm is greater than 25

Db.inventory.find ({"dim_cm.1": {$gt: 25}})

4. $size looks up according to the array length

Find a document with a tags length of 3

Db.inventory.find ({"tags": {$size: 3}})

5. $gte is greater than or equal to

5.1. Original data

Db.inventory.insertMany ([{item: "journal", instock: [{warehouse: "A", qty: 5}, {warehouse: "C", qty: 15})}, {item: "notebook", instock: [{warehouse: "C", qty: 5}]}, {item: "paper", instock: [{warehouse: "A", qty: 60}, {warehouse: "B", qty: 15}]}} {item: "planner", instock: [{warehouse: "A", qty: 40}, {warehouse: "B", qty: 5}]}, {item: "postcard", instock: [{warehouse: "B", qty: 15}, {warehouse: "C", qty: 35}]}])

5.2.Lookup a collection of documents whose qty of the first element (object) of the array is greater than or equal to 20

Db.inventory.find ({'instock.0.qty': {$gte: 20}})

6. The properties of the $elemMatch object match

Find an object in the array that conforms to qty=5, warehouse= "A", and return the document collection

Db.inventory.find ({"instock": {$elemMatch: {qty: 5, warehouse: "A"})

6.2. find a collection of documents in the array whose qty is greater than 10 and less than or equal to 20

Db.inventory.find ({"instock": {$elemMatch: {qty: {$gt: 10, $lte: 20})

If you do not use $elemMatch, it means that the qty is greater than 10 or less than or equal to 20. The official document means that instead of looking for a qty that satisfies both condition An and condition B in an element of the array, it looks for a qty that satisfies both condition An and condition B on all elements of the array.

Db.inventory.find ({"instock.qty": {$gt: 10, $lte: 20}})

7. $slice returns elements at a specific location in the array

7.1. Original data

Db.inventory.insertMany ([{item: "journal", qty: 25, tags: ["blank", "red"], dim_cm: [14,21]}, {item: "notebook", qty: 50, tags: ["red", "blank"], dim_cm: [14,21]}, {item: "paper", qty: 100, tags: ["red", "blank", "plain"], dim_cm: [14 21]}, {item: "planner", qty: 75, tags: ["blank", "red"], dim_cm: [22.85,30]}, {item: "postcard", qty: 45, tags: ["blue"], dim_cm: [10,15.25]}])

Find and return the last element of the tags array

Db.inventory.find ({item: "journal"}, {item: 1, qty: 0, tags: {$slice:-1}})

Results:

{"_ id": ObjectId ("5c91dce5e98d5972748780e6"), "item": "journal", "tags": ["red"]}

8. $type returns elements of the specified type

8.1. Original data

Db.inventory.insertMany ([{_ id: 1, item: null}, {_ id: 2}])

8.2. Return data of type null

Db.inventory.find ({item: {$type: 10}})

The types are as follows:

For more information, please see https://docs.mongodb.com/manu....

9. $exists returns keys that exist / do not exist

Find data that does not have an item key

Db.inventory.find ({item: {$exists: false}})

10. $all contains

10.1. Original data

Db.inventory.insertMany ([{item: "journal", qty: 25, tags: ["blank", "red"], dim_cm: [14,21]}, {item: "notebook", qty: 50, tags: ["red", "blank"], dim_cm: [14,21]}, {item: "paper", qty: 100, tags: ["red", "blank", "plain"], dim_cm: [14 21]}, {item: "planner", qty: 75, tags: ["blank", "red"], dim_cm: [22.85,30]}, {item: "postcard", qty: 45, tags: ["blue"], dim_cm: [10,15.25]}])

10.2. Find documents that contain ["red", "blank"] in the tags array

Db.inventory.find ({tags: {$all: ["red", "blank"]}})

To sum up:

Array: $all, $size, $slice

Object: $elemMatch

The above is all the contents of the article "what are the Query operations commonly used in MongoDB". Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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