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[experience sharing] summary of database operations commonly used in Django development

2022-06-28 13:39:00 【Tencent blue whale assistant】

Query class operation

1） Query all results , Quite a sql Medium select * from

list = Test.objects.all()

2） Conditions of the query ,filter relevant sql Medium where, Used to filter query results

Pass multiple parameters ：result = Test.objects.filter(id=1, name=’test’)

If multiple conditions and queries , Directly separated by commas ,filter The arguments in the function are Test Model In the field

3） Get single object ,get Method parameters are generally Model Primary key of , If you can't find it, you will report an error

test_obj = Test.objects.get(id=1)

4） Limit the amount of result data returned , amount to sql Medium limit, among order_by Yes for sorting , If according to the field a Reverse sort , Namely order_by(“-time”)

Test.objects.order_by('name')[0:2]

5） Chain query

Test.objects.filter(name=’test’).order_by(“-ctime”)

6） Multi condition parameter query , A dictionary , Construct query conditions

data = Test.objects.filter(**query_dict).order_by(“-ctime”).values

among query_dict For a dictionary ,key Is a condition field ,value Is the condition value

query_dict = {'id':123,'name':’yyp’}

7） Pass on Q object , Construct query conditions

stay filter() The keyword parameters in the equivalent function are all “and” Relationship . But to execute more complex queries ( such as , Implement the filter criteria or Relationship ), have access to Q object .
Q Objects include AND Relationship and OR Relationship
Q Objects can be used & and | Operator to connect . When an operation connects two Q Object time , A new equivalent Q object

1、 First step , structure Q object ：

fromdjango.db.models import Q

Q(name__startswith=’h’) | Q(name__startswith=’p’)

2、 The second step ,Q Object is used as a query parameter , Multiple Q The object is and Relationship ：

Test.objects.filter(

Q(date=’2018-10-10 00:00:00’),

Q(name__startswith=’h’) | Q(name__startswith=’p’)

filter() And so on Q Object and condition parameters , but Q The object must precede the condition parameter

8） Filter operations that do not meet the conditions

data = Test.objects.exclude(id=1)

Pass in condition query

q1 = Q()
q1.connector = 'OR'              # How to connect 
q1.children.append(('id', 1))
q1.children.append(('id', 2))
q1.children.append(('id', 3))

models.Tb1.objects.filter(q1)

Merge condition query

con = Q()

q1 = Q()
q1.connector = 'OR'
q1.children.append(('id', 1))
q1.children.append(('id', 2))
q1.children.append(('id', 3))

q2 = Q()
q2.connector = 'OR'
q2.children.append(('status', ' On-line '))

con.add(q1, 'AND')
con.add(q2, 'AND')

models.Tb1.objects.filter(con)

Add class operation

1） Add a record

test1 = Test(name=’yyp’)

test1.save()

Update class operations

1） First query to get the object , Then modify the value of the object , Save again

test1 = Test.objects.get(id=1)

test1.name = ‘Google’

test1.save()

2） Conditional chain update

Test.objects.filter(id=1).update(name=‘Google’)

Delete class operation

1） First query to get the object to be deleted , And then directly delete operation

// Delete id=1 The data of

test1 = Test.objects.get(id=1)

test1.delete()

2） Conditions delete

Test.objects.filter(id=1).delete()

QuerySet relevant

Django in model The structure type queried is QuerySet, It is essentially a set of query objects .

1） Convert multiple query results into dictionary lists

// all() Method to query QuerySet, use values Method to a dictionary set

data= Test.objects.all().values()

data_dict_list = list(data)

<QuerySet [<Test: test>]> ----><QuerySet [{“id”:XXX, “name”:XXX}]>

2）QuerySet Object to dictionary object

fromdjango.forms.models import model_to_dict

data = Test.objects.get(id=1)

data_dict = model_to_dict(data)

3） Serialized into json data

For many web When developing interfaces , To return is json data , and django from DB The query results in a set of objects , You can consider django-rest-framework Library serializers class , For details, please refer to ：Tutorial 1: serialize

Summary of query criteria

Field name __op:

__exact  Exactly equal to  like ‘aaa’

__iexact Precision is equal to ignoring case ilike‘aaa’

__contains  contain  like ‘%aaa%’

__icontains Include ignore case ilike‘%aaa%’, But for sqlite Come on ,contains The effect is the same as icontains.

__gt Greater than 

__gte Greater than or equal to 

__lt Less than 

__lte Less than or equal to 

__in  Exist in a list Within the scope of 

__startswith With … start 

__istartswith With … Ignore case at the beginning 

__endswith With … ending 

__iendswith With … ending , Ignore case 

__range  stay … Within the scope of 

__year  The year of the date field 

__month  The month of the date field 

__day  Date of the date field 

__isnull=True/False

Use sql Statement to query

fromdjango.db import connection

cursor = connection.cursor()

cursor.execute(“select * from Test where name = %s”, "yyp")

row = cursor.fetchone()

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