MongoDB Learning notes < four >

Today continue to learn about MongoDB's knowledge, mainly including the following for example:

--find Specific explanations

--Pagination and sorting

-Cursors and other knowledge

1. Specify the key to return

Db.person.find ({},{"_id": 0, "name": 1, "Country": 1}) This simply queries the name key and the country key, noting that the other assumptions do not appear by default, but assume that the _id hypothesis is not written and is displayed by default.

2. Query criteria

Db.person.find ({"Age": {$gte: +, $lte: 27}},{"_id": 0, "name": 1, "Country": 1}) Check the name and country of the student aged 25-27.

Db.person.find ({"Country": {$ne: "Korea"}},{"_id": 0, "math": 1}) query all not the math scores of Korean students

3. Include or not include

$in or $nin

Db.person.find ({"Country": {$in: ["USA", "China"]}},{"_id": 0, "math": 1}) Query nationality is an American or Chinese student's math score

Db.person.find ({"Country": {$nin: ["USA", "China"]}},{"_id": 0, "math": 1}) Query nationality is not an American or Chinese student's math score

4.or Query

$or

Db.person.find ({$or: [{"Chinese": {$gt: 85}},{"中文版": {$gt: 90}}]},{"_id": 0, "name": 1, "Chinese": 1, "中文版": 1}) Query for student information with a language score greater than 85 or English bar with a score greater than 90

5. Regular queries

Db.person.find ({name:/li/i},{"_id": 0, "name": 1}) The name of the student whose name contains "Li"

6. Use of $not

Db.person.find ({name:{$not:/li/i}},{"_id": 0, "name": 1}) name of the student whose name does not contain "Li"

Note: The difference between $not and $nin is that $not can be used wherever, and $nin can only be used on the set

7. Array query $all and index applications

Query the students who like to look at the two books MongoDB and JS

Db.person.find ({books:{$all: ["MongoDB", "JS"]}},{"_id": 0, "name": 1})

Query the second book is the student information of Java

Db.person.find ({"Books.1": "JAVA"})

8. Querying the specified length array size

Db.person.find ({"Books": {$size: 4}})

9. Find out the number of Jim's books

var Jim =  db.person.find ("name": "Jim") while (Jim.hasnext ()) {   obj = Jim.next ();   Print (Obj.books.length)}

The $slice operator returns the internal value of the specified array in the document.

Find out the 第2-4 book in Jim's Bookshelf

Db.person.find ({"Name": "Jim"},{books:{$slice: [1,3]}})

Check out the last book

Db.person.find ({"Name": "Jim"},{books:{$slice:-1}})

This time first, go ahead, cursor and sort.

MongoDB Learning notes < four >