04 summary of various query operations and aggregation operations of mongodb

Catalog ： The basic chapter （ Can solve the problem of 80 The problem of ）
01 MongoDB Overview 、 Application scenarios 、 Download mode 、 Connection mode and development history, etc

02 MongoDB data type 、 Key concepts and shell Commonly used instructions

03 MongoDB Various additions to documents 、 to update 、 Delete operation summary

04 MongoDB Various query operations And summary of aggregation operations

05 MongoDB Summarize the various operations of the column

python3 operation MongoDB Various cases of

One . Use find() Method to query documents

Grammar format : db.collection.find(query, projection)

explain : find() Method to display all documents in an unstructured manner , Parameters can be specified ：

query : Optional , Use the query operator to specify the query criteria ;
projection : Optional , Use the projection operator to specify the returned key . Returns all key values in the document when queried , Simply omit the parameter （ The default is omitted ）.

Case study 1: Such as directed set user_demo The query name in is zhangsan Users of :

db.user_demo.find({
    'name':'zhangsan'})

#  amount to sql Medium 
select * from user_demo where name = "zhangsan";

Case study 2： Specifies which keys are returned

db.article.find({
    }, {
    "title": 1, "author": 1})

#  amount to sql Medium 
select title, author from article;

except find() Out of the way , One more findOne() Method , It returns only one document .

Two . AND Query and OR Inquire about

2.1 AND Inquire about

AND Query syntax format : db.col.find({key1:value1, key2:value2})

Case study 1: Such as directed set user_demo The query name in is zhangsan And age by 20 The data of :

db.user_demo.find({
    'name':'zhangsan', 'age': 20})

#  amount to sql Medium 
select * from user_demo where name = "zhangsan" and age = 20;

2.2 OR Inquire about

OR Query syntax format :

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

Case study 2: Such as directed set user_demo The query name in is zhangsan Users or age by 20 The data of :

db.user_demo.find({
    $or:[{
    'name':'zhangsan', 'age': 20}]})

#  amount to sql Medium 
select * from article where name = "zhangsan" or age = 20;

Case study 3: AND and OR Joint use cases , Similar to the conventional SQL Statement for ：

db.col.find({
    "likes": {
    $gt:50}, $or: [{
    "by": "xx course "},{
    "title": "MongoDB  course "}]})

#  amount to sql Medium 
select * from col where likes>50 AND (by = 'xx course ' OR title = 'MongoDB  course ');

3、 ... and . Conditional operators

3.1 Comparison conditions

MongoDB The conditional operators in are ：

(>) Greater than - $gt
(<) Less than - $lt
(>=) Greater than or equal to - $gte
(<= ) Less than or equal to - $lte

Case study 1: obtain “col” Collection “likes” Greater than 100 The data of ：

db.col.find({
    likes : {
    $gt : 100}})

#  amount to sql Medium 
select * from col where likes > 100;

Case study 2: obtain "col" Collection “likes” Greater than or equal to 100 The data of ：

db.col.find({
    likes : {
    $gte : 100}})

#  amount to sql Medium 
select * from col where likes >= 100;

Case study 3: obtain "col" Collection “likes” Less than 150 The data of ：

db.col.find({
    likes : {
    $lt : 150}})

#  amount to sql Medium 
select * from col where likes < 150;

Case study 4: obtain "col" Collection “likes” Less than or equal to 150 The data of ：

db.col.find({
    likes : {
    $lte : 150}})

#  amount to sql Medium 
select * from col where likes <= 150;

Case study 5: obtain "col" Collection “likes” Greater than 100, Less than 200 The data of ：

db.col.find({
    likes : {
    $lt :200, $gt : 100}})

#  amount to sql Medium 
select * from col where likes > 100 and likes < 200;

Case study 6: obtain "col" Collection “likes” It's not equal to 100 The data of ：

db.col.find({
    likes : {
    "$ne": 100}})

#  amount to sql Medium 
select * from col where likes != 100;

3.2 in Conditions

select * from article where author in ("a", "b", "c")

#  amount to sql Medium 
db.article.find({
    "author": {
    "$in": ["a", "b", "c"]}})

3.3 like Conditions of the query

db.article.find({
    "title": /mongodb/})

#  amount to sql Medium 
select * from article where title like "%mongodb%"

Four . limit() Methods and skip() Method

4.1 Control the number of returns limit() Method

Grammar format (limit)：db.COLLECTION_NAME.find().limit(NUMBER)

For example, two records in the query document are displayed ：

db.col.find({
    },{
    "title":1}).limit(2)

Except that it can be used limit() Method to read a specified amount of data , You can also use skip() Method to skip a specified amount of data ,skip Method also accepts a numeric parameter as the number of records to skip .

4.2 Skip the quantity skip() Method

Grammar format ：db.COLLECTION_NAME.find().limit(NUMBER).skip(NUMBER)

The following example shows only the second document data :

db.col.find({
    },{
    "title":1).limit(1).skip(1)

#  The following is the skip before 5 Data , That is from the 6 Start to return to .
db.article.find().skip(5)

notes :skip() The default parameter of the method is 0 .

4.3 limit and skip combination

Can combine limit() and skip() To achieve paging effect ：

db.article.find().skip(10).limit(20) 

#  amount to sql Medium  
select * from article limit 10, 20;

5、 ... and . Sort sort() Method

stay MongoDB Use in sort() Method to sort the data .

sort() Method can be used to specify the sorting field by parameter , And use 1 and -1 To specify how to sort , among 1 Arrange... In ascending order , and -1 It's for descending order .

Grammar format ：db.COLLECTION_NAME.find().sort({KEY:1})

If in col Data in the collection by field likes Descending order of ：

db.col.find({
    },{
    "title":1}).sort({
    "likes":-1})

#  amount to sql Medium 
select * from col where title = 1 order by likes desc;

Be careful ：skip(), limilt(), sort() When the three are put together , The order of execution is first sort(), And then there was skip(), Finally, it shows limit().

6、 ... and . $type The operator

6.1 MongoDB The types that can be used in are shown in the following table ：

• Double 1
• String 2
• Object 3
• Array 4
• Binary data 5
• Undefined 6 obsolete .
• Object id 7
• Boolean 8
• Date 9
• Null 10
• Regular Expression 11
• JavaScript 13
• Symbol 14
• JavaScript (with scope) 15
• 32-bit integer 16
• Timestamp 17
• 64-bit integer 18
• Min key 255 Query with -1.
• Max key 127

Case study : obtain “col” Collection title by String The data of :
db.col.find({"title" : {$type : 2}}) or
db.col.find({"title" : {$type : 'string'}})

6.2 Query of multiple elements

Case study : Only type Arrays exist at the same time mongodb and javascript Will match .

db.article.find({
    "type": {
    "$all": ["mongodb", "javascript"]}})

6.3 Limit array length query

Case study : Only the length of the array is 2 Will match , notes ：type_list It must be an array

db.article.find({
    "type_list": {
    "$size": 2}})

6.4 Returns a specific quantity

When $slice When the parameter of is a , Represents the number of returns ; When it's an array , The first parameter is the offset , The second represents the number of returns ：

Case study ： Returns a specific quantity , notes ：$slice For arrays

db.article.find({
    "type": {
    "$slice": 1}}) //  Back to page 1 individual 

db.article.find({
    "type": {
    "$slice": -1}})  //  Go back to the last 

db.article.find({
    "type": {
    "$slice": [20, 10]}})  //  From 21 Start , return 10 individual , That is to say 21～30

For more types, please refer to ：mongodb $type

7、 ... and . MongoDB Special sentences

7.1 Element match ($elemMatch)

If there is a field in the document whose value is an array , have access to $elemMatch To match elements in an array ：

Case study ： Only a=1 And b>2 Will match .

db.article.find({
    "kown": {
     "$elemMatch": {
    a: 1, b: {
    "$gt": 2}}}})

7.2 modulus （$mod）

For example, we need to match read % 5 == 1：

db.article.find({
    "read": {
    $mod: [5, 1]}})

7.3 Whether there is （$exists)

If we want to judge love Whether the field exists , It can be like this ：

#  If there are fields love, Just go back to 
db.article.find({
    "love": {
    "$exists": true}})

#  We can also judge that it doesn't exist ,  If there are no fields love, Just go back to 
db.article.find({
    "love": {
    "$exists": false}})

7.4 Regular expressions

mongodb regular expression , The usage is the same as regular literal quantity ：

# i Ignore case 
db.article.find({
    "title": /mongodb/i})

7.5 Types of queries

We can return data according to the field type ：

#  Only when comments The type of is array 
db.article.find({
    "comments": {
    "$type": 4}})

7.6 Embedded documents

mongodb Is allowed to embed documents , And it's easy to query embedded documents （ Use point Syntax ）：

{
    
  address: {
     name: "nanji" }
}

db.article.find({
    "address.name": "nanji"})

Arrays can also take point Syntax :

{
    
  comments: [{
    title: "mongodb"}, {
    title: "javascript"}]
}

db.article.find({
    "comments.title": "mongodb"})

7.7 Take the opposite

$not It's a meta statement , It can be applied to any other condition ：

db.article.find({
    "author": {
    "$not": /mongodb/i}})

Just use $not The operator , It means reverse .

7.8 Statistics

Returns the length of the matching data ：

db.article.find().count()

7.9 format

pretty() Method to display all documents in a formatted way ：

db.article.find().pretty()

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