MongoDB Study Notes

Find Method

DB. collection_name.find ();

 

Query all results:

Select * from users;

DB. Users. Find ();

Specify the columns (KEYS) returned ):

Select name, skills from users;

DB. Users. Find ({},{ 'name': 1, 'skills': 1 });

Note: The first {} puts the where condition and the second {} specifies the columns to display and not to display (0 indicates not to display 1 indicates to display)

Where condition:

1. Simple equals:

Select name, age, skills from users where name = 'hurry ';

DB. Users. Find ({'name': 'hurry'}, {'name': 1, 'age': 1, 'skills': 1 });

2. Use and

Select name, age, skills from users where name = 'hurry' and age = 18;

DB. users. find ({'name': 'hurry', 'age': 18}, {'name': 1, 'age': 1, 'skills': 1 });

3. Use or

Select name, age, skills from users where name = 'hurry' or age = 18;

DB. users. find ({'$ or': [{'name': 'hurry'}, {'age': 18}]}, {'name': 1, 'age ': 1, 'skills': 1 });

4. <, <=,>,> =($ Lt, $ LTE, $ GT, $ GTE)

Select * from users where age> = 20 and age <= 30;

DB. Users. Find ({'age': {'$ gte': 20,' $ LTE ': 30 }});

5. Use in, not in ($ in, $ Nin)

Select * from users where age in (10, 22, 26 );

DB. Users. Find ({'age': {'$ in': [10, 22, 26]});

6. Match null

Select * from users where age is null;

DB. Users. Find ({'age': NULL );

7. Like (MongoDB supports regular expressions)

Select * from users where name like "% HURRY % ";

DB. Users. Find ({Name:/Hurry /});

Select * from users where name like "Hurry % ";

DB. Users. Find ({Name:/^ hurry /});

8. Use distinct

Select distinct (name) from users;

DB. Users. Distinct ('name ');

9. Use count

Select count (*) from users;

DB. Users. Count ();

 

10. array query (MongoDB exclusive)

If skills is ['java', 'python']

DB. Users. Find ({'skills': 'java'}); this statement can be matched successfully.

$ All

DB. Users. Find ({'skills': {'$ all': ['java', 'python']}) skills must contain both Java and Python

$ Size

DB. Users. Find ({'skills': {'$ size': 2}) Unfortunately, $ size cannot be combined with $ lt.

$ Slice

DB. Users. Find ({'skills': {'$ slice: [1, 1]})

The two parameters are offset and return quantity respectively.

11. query embedded documents

12. Powerful $ where Query

DB. Foo. Find ();
{"_ Id": objectid ("4e17ce0ac39f1afe0ba78ce4"), "A": 1, "B": 3, "C": 10}
{"_ Id": objectid ("4e17ce13c39f1afe0ba78ce5"), "A": 1, "B": 6, "C": 6}

What if I want to query the document B = C?

> DB. Foo. Find ({"$ where": function (){

For (VAR current in this ){
For (VAR other in this ){
If (current! = Other & this [current] = This [other]) {
Return true;
}
}
}
Return false;

}});

 

{"_ Id": objectid ("4e17ce13c39f1afe0ba78ce5"), "A": 1, "B": 6, "C": 6}