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Query data

All the data that goes into mongodb is stored so that it can be retrieved when it needs to be read.

But instead of reading by a column such as score: read by sort; There will also be I only look at a certain period of time, a certain class of conditional screening; There will also be I want to see the average score of each class aggregate for average…. And so on

These operations can be done with find_one(), find() :

ret2find = collect.find_one()
# {'_id': ObjectId(' 5ea780BF747e3e128470e485 '), 'class_name': 'Student_name ', 'subject':' English ', 'score': 100, 'date': '20200301'}

ret2find = collect.find()
# <pymongo.cursor.Cursor object at 0x0000024BBEBE15C8>
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As you can see from the above results, find_one() query results in a single dictionary; Find () is a generator object that can be fetched by traversing for val in ret2find:

Setting search Conditions

But can take out all the data is not enough, query is generally with conditions, even complex conditions – such as: query out of three (1) class, Zhang SAN or Li Si, score more than 90 subjects, how to do?

ret2find = collect.find({"class_name":"Class 1, Senior 3"."score": {"$gt":90},"$or": [{"student_name":"Zhang"}, {"student_name":"Bill"}]})

for val in ret2find:
    print(val)
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There are two main points:

{“class_name”:” grade “,”score”:{“$gt”:90}}

Grade 3 (1) > 90

In addition to the $gt comparison operator, the table is greater than the meaning.

symbol meaning
$lt Less than
$lte Less than or equal to
$gt Is greater than
$gte Greater than or equal to
$ne Is not equal to
$in Within the scope of
$nin Out of range

{$” or “: [{” student_name” : “* *”}, {” student_name “:” bill “}]}

The student’s name is Zhang SAN or Li Si.

The $or logical operator is used to indicate the relationship between conditions. Other logical operators besides $or include:

symbol meaning
$and Take the intersection conditionally
$not The opposite set of a single condition
$nor The opposite set of conditions
$or A union of conditions

More Query Operations

In addition to the above general operations, we will also use in specific scenarios:

symbol meaning The sample The sample mean
$regex Regular match {“student_name”:{“
r e g e x ” : ” . ∗ three Regex “:”. * 3 “}}		 The student’s name ends in three
$expr Aggregate expressions are allowed in queries {“expr”:{“gt”:[“
s p e n t ” . ” spent”,” budget”]}}		 Query records for overruns that cost more than budgeted
$exists Whether the attribute exists {“date”:{“$exists”: True}} Date attribute exists
$exists Whether the attribute exists {“date”:{“$exists”: True}} Date attribute exists
$type Type judgment {“score”:{“$type”:”int”}} The type of score is int
$mod Modulus operation {‘score’: {‘$mod’: [5, 0]}} The fraction is modulo 5 and 0

More query operators can be found in the official documentation