MongoDB (2): Delete and change the operation

Additional commands:

1. Enter the front-end Operation command

./mongo [IP: Port]

Description: Local is automatically selected by default, Port 27017

2. Show All libraries

> Show DBS; or show databases;

3. Select Library

> Use library name;

4. Display all the collections of the library

> Show Collections; or show tables;

5. Display the currently used library

> db;

I. Operating database, Documentation

1.1. Database operation

1. Create a database: MongoDB does not have a specific statement to create a database, you can use "using" to use a database, if you want to use

Database does not exist, you will create one that will be saved as a file after you actually add a document to the library.

> Use db_test;

2, delete the database, command: Db.dropdatabase (), note first to go to the library to be deleted

> Use db_test;switched to DB db_test> db.dropdatabase (); {"OK": 1}>

1.2. Set operation

1. Create a collection: You do not have to create a collection in MongoDB because there is no fixed structure, directly using the DB. Set name. command to operate on it. If you want to display the Create collection, use: Db.createcollecion ("collection name");

2. Delete collection, command: Dorp

> Db.test1.drop ();

1.3. View the status information for a collection

Db. Collection name. Stats ();

Second, increase the deletion

2.1. Add

Db. Collection name. Insert (data);

> Db.test1.insert ({"username": "Zhangsan", age:2});

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Insert method, you can insert a single document, or you can insert multiple, with "[]". Attention:

1:mongodb automatically adds a "_id" field for each document that does not have a "_id" field

2: Each doc must be less than 16MB

3: Object.bsonsize (document name) can be executed in shell, to see size

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2.2. Delete

Command: Remove, can be removed by condition

Just delete the document, the collection is still there, if you use the Drop command, the collection and index will be deleted

> Db.test1.remove ({age:2});

Note: If you use remove without a condition, all documents in this collection are deleted.

2.3. Update

Db. Collection name. Update (condition, new document);

> db.test1.update ({"userid": "1"},{"userid": "1", "username": "Zhangsan", "Age": 10});

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Problem:

1. If there are multiple documents matching, only the first document will be updated.

2, this modification is the entire document

Solve:

Using modifiers

Update modifier for complex update operations

1: $set: Specifies the value of a field, if the field does not exist, creates a

> db.test1.update ({"UserId": "1"},{"$set": {"username": "Zhangsan"}},0,1);

Description: If the UserID is 1, update its username to Zhangsan

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> db.test1.update ({"UserId": "1"},{$set: {"score.1": 7}});

Description: Update the array score with a value of 1 for index 7, and the index to start at 0.

2: $unset: Remove a field

> db.test1.update ({"UserId": "1"},{"$unset": {"username": 1}},0,1);

3: $inc: Used to increase the value of an existing key, and if the field does not exist, one is created. Can only be used for integers, long integers, or double-precision floating-point values.

> db.test1.update ({"UserId": "1"},{"$inc": {"age": 3}},0,1);

Description: If the UserID is 1, the value of age is increased by 3

4: $push: Add an element to the end of an existing array, or create a new array if not

> db.test1.update ({"UserId": "1"},{"$push": {"score": 1}},0,1);

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5: $each: Manipulate multiple values with one $push

> db.test1.update ({"UserId": "1"},{"$push": {"score": {$each: [4,5,6]}}},0,1];

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6: $slice: The limit array contains only the last n elements, whose value must be a negative integer

> db.test1.update ({"UserId": "1"},{"$push": {"score": {$each: [7,8,9], $slice:-5}});

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7: $sort: Elements in an array, sorts the data according to the specified fields (1 is ascending,-1 is descending), and then it is deleted by slice.

Note: You cannot use only $slice or $sort with $push, and you must use $each

> db.test1.update ({"UserId": "1"},{"$push": {"score": {$each: [], $slice: -5, $sort:-1}});

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8: $ne: Determine if a value is in an array, and if not, add it in

> db.test1.update ({"UserId": "1", "score": {$ne: 4}},{$push: {"Score": 4}});

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9: $addToSet: Use the array as a dataset to ensure that the elements within the array are not duplicated

> db.test1.update ({"UserId": "1"},{$addToSet: {"score": 8}});

: $pop: Delete the element from the end of the array, {$pop: {key:1}}, delete one from the end, 1 remove from the head

> db.test1.update ({"UserId": "1"},{$pop: {score:1}});

All: $pull: Delete all matching elements by condition

> db.test1.update ({"UserId": "1"},{$pull: {score:7}});

12:$: Used to modify the first matching element

> db.test1.update ({"score.0": 5},{$set: {"score.$": 7}});

Description: If the No. 0 index value of score is 5, the No. 0 index value of update score is 7

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MongoDB (2): Delete and change the operation