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Django之 Models組件

 印度阿三17 2019-07-15

本節(jié)內(nèi)容

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  • 路由系統(tǒng)
  • models模型
  • admin?
  • views視圖
  • template模板

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引子

講django的models之前， 先來想一想， 讓你通過django操作數(shù)據(jù)庫，你怎么做？ 做苦思冥想，可能會這樣寫。

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 import?pymysql ? ? def?index(request): ????# 創(chuàng)建連接 ????conn?=?pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='alex123', db='luffy_dev') ????# 創(chuàng)建游標(biāo) ????cursor?=?conn.cursor() ? ????cursor.execute("select username,email,mobile from web_account") ????data_set?=?cursor.fetchall() ? ????cursor.close() ????conn.close() ? ????return?HttpResponse(data_set)

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很方便就實(shí)現(xiàn)了從數(shù)據(jù)庫里取數(shù)據(jù)，事實(shí)上，很多人確實(shí)就是這么做的。但這樣做會帶來2個問題

  • SQL注入危險，因為有的時候你操作數(shù)據(jù)庫的語句不是寫死在代碼里的，而是通過前端傳參數(shù)拼接的，這就給黑客有了可趁之機(jī)，通過拼接參數(shù)實(shí)現(xiàn)sql注入。
  • 語句跟代碼揉在一起了，增加后續(xù)維護(hù)成本

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那怎么辦呢？ORM提供了新思路。

什么是ORM呢？

對象關(guān)系映射(Object Relational Mapping)，它的實(shí)質(zhì)就是將關(guān)系數(shù)據(jù)（庫）中的業(yè)務(wù)數(shù)據(jù)用對象的形式表示出來，并通過面向?qū)ο螅∣bject-Oriented）的方式將這些對象組織起來，實(shí)現(xiàn)系統(tǒng)業(yè)務(wù)邏輯的過程。

在ORM過程中最重要的概念是映射（Mapping），通過這種映射可以使業(yè)務(wù)對象與數(shù)據(jù)庫分離。從面向?qū)ο髞碚f，數(shù)據(jù)庫不應(yīng)該和業(yè)務(wù)邏輯綁定到一起，ORM則起到這樣的分離作用，使數(shù)據(jù)庫層透明，開發(fā)人員真正的面向?qū)ο蟆?/p>

上面的解釋有點(diǎn)蒙蔽對不？其實(shí)你只需要抓住2個關(guān)鍵詞， “映射” 和 “對象”，就能知道orm是什么干什么的了。

  • 映射(Mapping) —— 把表結(jié)構(gòu)映射成類
  • 對象 —— 像操作類對象一樣，操作數(shù)據(jù)庫里的數(shù)據(jù)

映射

看下面的圖，就是直觀的例子，把右邊的表結(jié)構(gòu)映射成了左邊的類

?Sql語句到對象

ORM可以使你不用再寫原生SQL, 而是像操作對象一樣就可以實(shí)現(xiàn)對表里數(shù)據(jù)的增刪改查

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好棒棒，媽媽再也不用逼你寫原生sql啦！

但是不要開心太早，ORM確實(shí)提高了開發(fā)效率，并且降低了數(shù)據(jù)操作與代碼之間的耦合，不過有利就有弊，我們總結(jié)一下orm的優(yōu)缺點(diǎn)。

優(yōu)點(diǎn)：

  1. 實(shí)現(xiàn)了代碼與數(shù)據(jù)操作的解耦合
  2. 不需自己寫原生sql, 提高開發(fā)效率
  3. 防止SQL注入, 通過對象操作的方式，默認(rèn)就是防止sql注入的。

缺點(diǎn)：

  1. 犧牲性能， 對象到原生SQL勢必會有轉(zhuǎn)換消耗，對性能有一定的影響?
  2. 復(fù)雜語句力不從心， 一些復(fù)雜的sql語句，用orm對象操作的方式很難實(shí)現(xiàn)，就還得用原生sql

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講Django為什么說ORM? 哈，? 好啦，是時候該引出主角啦，因為Django的models基于架構(gòu)ORM實(shí)現(xiàn)的。

Models模型

Django 的models把數(shù)據(jù)庫表結(jié)構(gòu)映射成了一個個的類， 表里的每個字段就是類的屬性。我們都知道數(shù)據(jù)庫有很多字段類型，int,float,char等， Django的models類針對不同的字段也設(shè)置了不同的類屬性。

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 AutoField?????????#An IntegerField that automatically increments according to available IDs BigAutoField??????#A 64-bit integer, guaranteed to fit numbers from 1 to 9223372036854775807. BigIntegerField???#-9223372036854775808 to 9223372036854775807 BinaryField???????#A field to store raw binary data. It only supports bytes assignment BooleanField??? CharField DateField?????????#e.g 2019-04-27 DateTimeField?????#e.g 2019-04-27 17:53:21 DecimalField????? DurationField?????#storing periods of time ,e.g [DD] [HH:[MM:]]ss[.uuuuuu]" EmailField FileField?????????#存儲文件 FloatField ImageField????????#Inherits all attributes and methods from FileField, but also validates that the uploaded object is a valid image. IntegerField GenericIPAddressField?#IP地址，支持ipv4 NullBooleanField??????#Like a BooleanField, but allows NULL as one of the options PositiveIntegerField??#Like an IntegerField, but must be either positive or zero (0). Values from 0 to 2147483647 PositiveSmallIntegerField?#only allows positive? values from 0 to 32767 SlugField?# A slug is a short label for something, containing only letters, numbers, underscores or hyphens. SmallIntegerField TextField???#A large text field. TimeField???#A time, represented in Python by a datetime.time instance. URLField UUIDField???#A field for storing universally unique identifiers. Uses Python’s UUID class.

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除了普通的表字段，針對外鍵也有映射

1 2 3 4 ForeignKey??# 外鍵關(guān)聯(lián) ManyToManyField??#多對多 ? OneToOneField??# 1對1

　　

好啦，接下來就用django的orm來設(shè)計一個博客表。

需求

  1. 每個用戶有自己的賬戶信息
  2. 用戶可以發(fā)文章
  3. 文章可以打多個標(biāo)簽

根據(jù)需求，我們設(shè)計3張表

注意Article表和Tag表是屬于多對多關(guān)系，什么是多對多？即一個文章有多個標(biāo)簽，一個標(biāo)簽又可以屬于多個文章。?

比如上圖的Article表中id為3的文章 ，它的標(biāo)簽是4,26, 即投資、大文娛、社交， 你看“投資”這個標(biāo)簽同時還屬于文章2。 這就是多對多關(guān)系 ， 即many to many .?

那這種多對多的關(guān)系如何在表中存儲呢？難道真的像上圖中一樣，在Article表中加個tags字段，關(guān)聯(lián)Tag表里的多條數(shù)據(jù)，通過逗號區(qū)分？

這倒確實(shí)是個解決辦法。但是也有問題，一個字段里存多條紀(jì)錄的id,就沒辦法做查詢優(yōu)化了。比如不能做索引等。

所以若想實(shí)現(xiàn)多對多關(guān)系的高效存儲 查詢優(yōu)化，可以在Article and Tag表之間再搞出一張表。

這樣是不是就實(shí)現(xiàn)了多對多關(guān)聯(lián)？

yes, 沒錯， django也是這么做的， django 有個專門的字段，叫ManyToManyField, 就是用來實(shí)現(xiàn)多對多關(guān)聯(lián)的，它會自動生成一個如上圖一樣的第3張表來存儲多對多關(guān)系。

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正式的表結(jié)構(gòu)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 from?django.db?import?models ? # Create your models here. ? ? class?Account(models.Model): ????username?=?models.CharField(max_length=64,unique=True) ????email?=?models.EmailField() ????password?=?models.CharField(max_length=128) ????register_date?=?models.DateTimeField("注冊日期",auto_now_add=True) ????signature?=?models.CharField(verbose_name="簽名",max_length=128,blank=True,null=True) ? ? class?Article(models.Model): ????"""文章表""" ????title?=?models.CharField(max_length=255,unique=True) ????content?=?models.TextField("文章內(nèi)容") ????account?=?models.ForeignKey("Account",verbose_name="作者",on_delete=models.CASCADE) ????tags?=?models.ManyToManyField("Tag",blank=True) ????pub_date?=?models.DateTimeField() ????read_count?=?models.IntegerField(default=0) ? ? class?Tag(models.Model): ????"""文章標(biāo)簽表""" ????name?=?models.CharField(max_length=64,unique=True) ????date?=?models.DateTimeField(auto_now_add=True)

　　

我們發(fā)現(xiàn)，每個字段其實(shí)都是一個獨(dú)立的對象，一張表其實(shí)是很多類的組合。

上面好多字段里還跟了些參數(shù)，我們來看以下常用的：

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 null????????#If True, Django will store empty values as NULL in the database. Default is False. blank???????#If True, the field is allowed to be blank. Default is False. ? db_column???#The name of the database column to use for this field. If this isn’t given, Django will use the field’s name. db_index????#If True, a database index will be created for this field. default?????#The default value for the field. This can be a value or a callable object. If callable it will be called every time a new object is created. editable????# django admin中用，后面講 help_text???# django admin中用，后面講 primary_key?# If True, this field is the primary key for the model. unique??????#If True, this field must be unique throughout the table unique_for_date????#Set this to the name of a DateField or DateTimeField to require that this field be unique for the value of the date field. For example, if you have a field title that has unique_for_date="pub_date", then Django wouldn’t allow the entry of two records with the same title and pub_date. ? unique_for_month???#Like unique_for_date, but requires the field to be unique with respect to the month. unique_for_year??? verbose_name????#A human-readable name for the field. If the verbose name isn’t given, Django will automatically create it using the field’s attribute name

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還有幾個特殊的字段屬性需要單獨(dú)介紹下

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choices

An iterable (e.g., a list or tuple) consisting itself of iterables of exactly two items (e.g. [(A, B), (A, B) ...]) to use as choices for this field.

The first element in each tuple is the actual value to be set on the model, and the second element is the human-readable name.

1 2 3 4 5 6 7 8 9 10 11 12 class?Student(models.Model): ????YEAR_IN_SCHOOL_CHOICES?=?( ????????('FR',?'Freshman'), ????????('SO',?'Sophomore'), ????????('JR',?'Junior'), ????????('SR',?'Senior'), ????) ????year_in_school?=?models.CharField( ????????max_length=2, ????????choices=YEAR_IN_SCHOOL_CHOICES, ????????default=FRESHMAN, ????)

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ForeignKey.on_delete

當(dāng)一條記錄關(guān)聯(lián)的外鍵紀(jì)錄被刪除時，django 也會根據(jù)外鍵關(guān)聯(lián)限制的配置來決定如何處理當(dāng)前這條紀(jì)錄。舉例，如果你有個可以為null的外鍵關(guān)聯(lián),并且你想在本紀(jì)錄關(guān)聯(lián)的數(shù)據(jù)被刪除時，把當(dāng)前紀(jì)錄的關(guān)聯(lián)字段設(shè)為null,那就配置如下

1 2 3 4 5 6 user?=?models.ForeignKey( ????User, ????on_delete=models.SET_NULL, ????blank=True, ????null=True, )

這個on_delete就是決定在關(guān)聯(lián)對象被刪除時，如何處理當(dāng)前紀(jì)錄的，常用的參數(shù)如下：

  • CASCADE——Cascade deletes. Django emulates the behavior of the SQL constraint ON DELETE CASCADE and also deletes the object containing the ForeignKey.
  • PROTECT——Prevent deletion of the referenced object by raising ProtectedError, a subclass of django.db.IntegrityError.
  • SET_NULL——Set the ForeignKey null; this is only possible if null is True.
  • SET_DEFAULT——Set the ForeignKey to its default value; a default for the ForeignKey must be set.

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配置Django數(shù)據(jù)庫連接信息

Django支持多種數(shù)據(jù)庫，Sqlite、Mysql、Oracle、PostgreSQL，默認(rèn)的是小型文件數(shù)據(jù)庫Sqlite

1 2 3 4 5 6 DATABASES?=?{ ????'default': { ????????'ENGINE':?'django.db.backends.sqlite3', ????????'NAME': os.path.join(BASE_DIR,?'db.sqlite3'), ????} }

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咱們是干大事的人，怎么也得用個Mysql呀， 改成mysql 也so easy.

1 2 3 4 5 6 7 8 9 10 DATABASES?=?{ ????'default': { ????????'ENGINE':?'django.db.backends.mysql', ????????'NAME':?'my_db', ????????'USER':?'mydatabaseuser', ????????'PASSWORD':?'mypassword', ????????'HOST':?'127.0.0.1', ????????'PORT':?'3306', ????} }

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不過注意，python3 連接mysql的得使用pymysql,MysqlDB模塊300年沒更新了，但django默認(rèn)調(diào)用的還是MySQLdb, so pymysql有個功能可以讓django以為是用了MySQLdb. 即在項目目錄下的__init__.py中加上句代碼就好

1 2 3 import?pymysql ? pymysql.install_as_MySQLdb()

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不加的話，一會連接數(shù)據(jù)時會報錯噢 。

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同步數(shù)據(jù)庫　　

你在ORM定義的表結(jié)構(gòu)如何同步到真實(shí)的數(shù)據(jù)庫里呢？ 只需2條命令。但django只能幫你自動創(chuàng)建表，數(shù)據(jù)庫本身還是得你自己來。

1 create?database?my_db charset utf8;　　

　　

好了，可以同步了，說好只需2步。

1. 生成同步文件,?django自帶一個專門的工具叫migrations, 負(fù)責(zé)把你的orm表轉(zhuǎn)成實(shí)際的表結(jié)構(gòu)，它不旦可以幫自動創(chuàng)建表，對表結(jié)構(gòu)的修改，比如增刪改字段、改字段屬性等也都能自動同步。只需通過下面神奇的命令。

1 python manage.py makemigrations　　

?不出意外的話，會顯示類似以下信息

1 2 3 4 5 6 7 $ python manage.py makemigrations Migrations?for?'app01': ??app01/migrations/0001_initial.py ????- Create model Account ????- Create model Article ????- Create model Tag ????- Add field tags to article

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此時你會發(fā)現(xiàn)，你的app下的migrations目錄里多了一個0001_initial.py的文件 ，這個文件就是因為你這條命令而創(chuàng)建的，migrations工具就會根據(jù)這個文件來創(chuàng)建數(shù)據(jù)庫里的表。

2. 同步到數(shù)據(jù)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 $ python manage.py migrate Operations to perform: ??Apply all migrations: admin, app01, auth, contenttypes, sessions Running migrations: ??Applying contenttypes.0001_initial... OK ??Applying auth.0001_initial... OK ??Applying admin.0001_initial... OK ??Applying admin.0002_logentry_remove_auto_add... OK ??Applying app01.0001_initial... OK ??Applying contenttypes.0002_remove_content_type_name... OK ??Applying auth.0002_alter_permission_name_max_length... OK ??Applying auth.0003_alter_user_email_max_length... OK ??Applying auth.0004_alter_user_username_opts... OK ??Applying auth.0005_alter_user_last_login_null... OK ??Applying auth.0006_require_contenttypes_0002... OK ??Applying auth.0007_alter_validators_add_error_messages... OK ??Applying auth.0008_alter_user_username_max_length... OK ??Applying auth.0009_alter_user_last_name_max_length... OK ??Applying sessions.0001_initial... OK (venv_django2) Alexs-MacBook-Pro:mysite alex$

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此時登錄你的數(shù)據(jù)庫，會發(fā)現(xiàn)創(chuàng)建了好多張表

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 mysql> show tables; ---------------------------- | Tables_in_luffy_dev2?????? | ---------------------------- | app01_account????????????? |??#對應(yīng)Account表 | app01_article????????????? |??#對應(yīng)Article表 | app01_article_tags???????? |??#自動創(chuàng)建的Article to Tag的多對多關(guān)聯(lián)表 | app01_tag????????????????? |??#對應(yīng)Tag表 | auth_group???????????????? |??#下面這些，都是django 自帶的表，這個是自動用戶系統(tǒng)的組 | auth_group_permissions???? |??#自帶的組與權(quán)限的多對多關(guān)聯(lián)表 | auth_permission??????????? |??#自帶權(quán)限表 | auth_user????????????????? |??#用戶表 | auth_user_groups?????????? | | auth_user_user_permissions | | django_admin_log?????????? |??#現(xiàn)在你的無法理解?? | django_content_type??????? |??#現(xiàn)在你的無法理解 | django_migrations????????? |??#紀(jì)錄migartions工具同步紀(jì)錄的表 | django_session???????????? |??#現(xiàn)在你的無法理解 ---------------------------- 14 rows?in?set?(0.00 sec)

　　

好啦，表結(jié)構(gòu)也有了，我們可以往里面插數(shù)據(jù)啦。

之前說好的是可以不用SQL語句的，一點(diǎn)不騙你。

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用orm對表數(shù)據(jù)進(jìn)行增刪改查

先進(jìn)入已經(jīng)連接好數(shù)據(jù)庫的django python環(huán)境

1 2 3 4 5 6 7 (venv_django2) Alexs-MacBook-Pro:mysite alex$ python manage.py shell? Python 3.5.2 (v3.5.2:4def2a2901a5, Jun 26 2016, 10:47:25) [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin Type?"help",?"copyright",?"credits"?or?"license"?for?more?information. (InteractiveConsole) >>> >>> from app01?import?models

　　

創(chuàng)建

創(chuàng)建數(shù)據(jù)簡單的令人發(fā)指

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查

filter 支持很多的過濾條件，我們來看下：

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contains

包含，相當(dāng)于sql的like條件

1 Entry.objects.get(headline__contains='Lennon')

SQL equivalent:

1 SELECT?...?WHERE?headline?LIKE?'%Lennon%';

Note this will match the headline 'Lennon honored today' but not 'lennon honored today'.

icontains? 大小寫不敏感　　

　　

in

In a given iterable; often a list, tuple, or queryset.

1 Entry.objects.filter(id__in=[1,?3,?4])

SQL equivalent:

1 SELECT?...?WHERE?id?IN?(1, 3, 4);

You can also use a queryset to dynamically evaluate the list of values instead of providing a list of literal values:

1 2 inner_qs?=?Blog.objects.filter(name__contains='Cheddar') entries?=?Entry.objects.filter(blog__in=inner_qs)

This queryset will be evaluated as subselect statement:

1 SELECT?...?WHERE?blog.id?IN?(SELECT?id?FROM?...?WHERE?NAME?LIKE?'%Cheddar%')

　　

gt

1 Entry.objects.filter(id__gt=4)

SQL equivalent:

1 SELECT?...?WHERE?id > 4;

gte
Greater than or equal to.

lt
Less than.

lte
Less than or equal to.

startswith
Case-sensitive starts-with.

1 Entry.objects.filter(headline__startswith='Lennon')

SQL equivalent:

1 SELECT?...?WHERE?headline?LIKE?'Lennon%';

SQLite doesn’t support case-sensitive LIKE statements; startswith acts like istartswith for SQLite　　

istartswith
Case-insensitive starts-with.

endswith
Case-sensitive ends-with.

iendswith
Case-insensitive ends-with

　　

range
區(qū)間過渡，可對數(shù)字、日期進(jìn)行過濾

1 2 3 4 import?datetime start_date?=?datetime.date(2005,?1,?1) end_date?=?datetime.date(2005,?3,?31) Entry.objects.filter(pub_date__range=(start_date, end_date))

SQL equivalent:

1 SELECT ... WHERE pub_date BETWEEN?'2005-01-01'?and?'2005-03-31';

Warning！

Filtering a DateTimeField with dates won’t include items on the last day, because the bounds are interpreted as “0am on the given date”. If pub_date was a DateTimeField, the above expression would be turned into this SQL:

SELECT ... WHERE pub_date BETWEEN '2005-01-01 00:00:00' and '2005-03-31 00:00:00';
Generally speaking, you can’t mix dates and datetimes.　

　　

date

For datetime fields, casts the value as date. Allows chaining additional field lookups. Takes a date value.　　

1 2 Entry.objects.filter(pub_date__date=datetime.date(2005,?1,?1)) Entry.objects.filter(pub_date__date__gt=datetime.date(2005,?1,?1))

year
For date and datetime fields, an exact year match. Allows chaining additional field lookups. Takes an integer year.

1 2 Entry.objects.filter(pub_date__year=2005) Entry.objects.filter(pub_date__year__gte=2005)

SQL equivalent:

1 2 SELECT?...?WHERE?pub_date?BETWEEN?'2005-01-01'?AND?'2005-12-31'; SELECT?...?WHERE?pub_date >=?'2005-01-01';

When USE_TZ is True, datetime fields are converted to the current time zone before filtering. 簡單解決辦法是把USE_TZ=False

month
For date and datetime fields, an exact month match. Allows chaining additional field lookups. Takes an integer 1 (January) through 12 (December).

1 2 Entry.objects.filter(pub_date__month=12) Entry.objects.filter(pub_date__month__gte=6)

When?USE_TZ?is?True, datetime fields are converted to the current time zone before filtering. This requires?time zone definitions in the database.

SQL equivalent:

1 2 SELECT?...?WHERE?EXTRACT('month'?FROM?pub_date) =?'12'; SELECT?...?WHERE?EXTRACT('month'?FROM?pub_date) >=?'6';

day
For date and datetime fields, an exact day match. Allows chaining additional field lookups. Takes an integer day.

1 2 Entry.objects.filter(pub_date__day=3) Entry.objects.filter(pub_date__day__gte=3)

SQL equivalent:

1 2 SELECT?...?WHERE?EXTRACT('day'?FROM?pub_date) =?'3'; SELECT?...?WHERE?EXTRACT('day'?FROM?pub_date) >=?'3';

　　

week

New in Django 1.11.

For date and datetime fields, return the week number (1-52 or 53) according to?ISO-8601, i.e., weeks start on a Monday and the first week contains the year’s first Thursday.

Example:

1 2 Entry.objects.filter(pub_date__week=52) Entry.objects.filter(pub_date__week__gte=32, pub_date__week__lte=38)

week_day

For date and datetime fields, a ‘day of the week’ match. Allows chaining additional field lookups.

Takes an integer value representing the day of week from 1 (Sunday) to 7 (Saturday).

Example:

1 2 Entry.objects.filter(pub_date__week_day=2) Entry.objects.filter(pub_date__week_day__gte=2)

hour

For datetime and time fields, an exact hour match. Allows chaining additional field lookups. Takes an integer between 0 and 23.

Example:

1 2 3 Event.objects.filter(timestamp__hour=23) Event.objects.filter(time__hour=5) Event.objects.filter(timestamp__hour__gte=12)

SQL equivalent:

1 2 3 SELECT?...?WHERE?EXTRACT('hour'?FROM?timestamp) =?'23'; SELECT?...?WHERE?EXTRACT('hour'?FROM?time) =?'5'; SELECT?...?WHERE?EXTRACT('hour'?FROM?timestamp) >=?'12';同　　

同時，還支持mintue,second

1 2 3 4 Event.objects.filter(time__minute=46) ? ? Event.objects.filter(timestamp__second=31)

isnull

Takes either?True?or?False, which correspond to SQL queries of?IS?NULL?and?IS?NOT?NULL, respectively.

Example:

1 Entry.objects.filter(pub_date__isnull=True)

SQL equivalent:

1 SELECT?...?WHERE?pub_date?IS?NULL;

regex

Case-sensitive regular expression match.

Example:

1 Entry.objects.get(title__regex=r'^(An?|The) ')

SQL equivalents:

1 2 3 4 5 6 7 SELECT?...?WHERE?title REGEXP?BINARY?'^(An?|The) ';?-- MySQL ? SELECT?...?WHERE?REGEXP_LIKE(title,?'^(An?|The) ',?'c');?-- Oracle ? SELECT?...?WHERE?title ~?'^(An?|The) ';?-- PostgreSQL ? SELECT?...?WHERE?title REGEXP?'^(An?|The) ';?-- SQLite　　

iregex?大小寫不敏感　　　　

　　　

改刪

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 # 批量修改 models.Account.objects.filter(username='elina').update(password="Luffy#21") ? # 單條修改 obj?=?models.Account.objects.get(username='linux') obj.username?=?'python' obj.save() ? ? # 批量刪除 models.User.objects.get(password='oldboy').delete() ? # 單條刪除 obj?=?models.User.objects.get(id=3) obj.delete()

?

?

數(shù)據(jù)返回后的展示

values()

values(*fields,?**expressions)

Returns a?QuerySet?that returns dictionaries, rather than model instances, when used as an iterable.

1 2 3 4 >>> Blog.objects.values() <QuerySet [{'id':?1,?'name':?'Beatles Blog',?'tagline':?'All the latest Beatles news.'}]> >>> Blog.objects.values('id',?'name') <QuerySet [{'id':?1,?'name':?'Beatles Blog'}]>

order_by()

order_by(*fields)

By default, results returned by a?QuerySet?are ordered by the ordering tuple given by the?ordering?option in the model’s?Meta. You can override this on a per-QuerySet?basis by using the?order_by?method.

1 Entry.objects.filter(pub_date__year=2005).order_by('-pub_date',?'headline')

The result above will be ordered by?pub_date?descending, then by?headline?ascending. The negative sign in front of?"-pub_date"indicates?descending?order. Ascending order is implied.?

reverse()

Use the?reverse()?method to reverse the order in which a queryset’s elements are returned. Calling?reverse()?a second time restores the ordering back to the normal direction.

To retrieve the “l(fā)ast” five items in a queryset, you could do this:

1 my_queryset.reverse()[:5]

　　

ORM對象操作

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 單表對象操作 o?=?models.Article.objects.all()[0] o.tilte ? 外鍵關(guān)聯(lián) >>> o.account.username 'jack' >>> o.account.username?=?rain ? 外鍵反向關(guān)聯(lián)操作 >>> a?=?models.Account.objects.get(username='alex') >>> a.article_set.all() <QuerySet [<Article: 你好，2018>]> >>> a.article_set.select_related() <QuerySet [<Article: 你好，2018>]> ? ? 多對多操作 >>> o?=?models.Article.objects.all()[1] >>> o.tags.all() <QuerySet [<Tag: 投資>, <Tag: 科技>]> ? ? 多對多反向操作 >>> t?=?models.Tag.objects.get(name="投資") >>> t.article_set.all() <QuerySet [<Article: 你好，2018>, <Article: 粉絲超過10萬后，我經(jīng)歷了抖音盜號風(fēng)波>]>

　　

　　

?

好啦，orm的操作先點(diǎn)到為止，后面學(xué)項目時再帶你搞復(fù)雜的。

練習(xí)題

  1. 基于前面課程設(shè)計的表結(jié)構(gòu)，完成以下練習(xí)：
  2. 創(chuàng)建5條account和5條新tag紀(jì)錄
  3. 創(chuàng)建5條article信息，關(guān)聯(lián)上面的不同的用戶和tag
  4. 在account表里找到用戶名包含al的紀(jì)錄，然后把密碼改掉
  5. 在article表找到文章內(nèi)容包含“電影”2個字的，把這些文章加上”大文娛”tag
  6. 把用戶elina發(fā)表的文章找出來，并且把作者都改成alex
  7. 找到用戶表里注冊日期在2018-04月，并且signature為空的紀(jì)錄
  8. 打到文章中標(biāo)簽為“投資”的所有文章
  9. 找到每個月8號注冊的用戶
  10. 找到每年5月發(fā)表的文章?
  11. 找到2015-2017年5月發(fā)表的文章?
  12. 找到文章作者以’a’或’k’開頭的文章

　　

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