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Peewee字段类

2021-09-02 分类：Peewee教程 阅读(1414) 评论(0)

模型(Model)类包含一个或多个属性，这些属性是 Peewee 中 Field 类的对象。Base Field 类不是直接实例化的。Peewee 为等效的 SQL 数据类型定义了不同的子类。

Field 类的构造函数具有以下参数

Sr.No Constructor & Description
1 column_name (str)
Specify column name for field.
2

primary_key (bool)
Field is the primary key.
3

constraints (list)
List of constraints to apply to column
4

choices (list)
An iterable of 2-tuples mapping column values to display labels.
5

null (bool)
Field allows NULLs.
6

index (bool)
Create an index on field.
7

unique (bool)
Create an unique index on field.
8

Default
Default value.
9

collation (str)
Collation name for field.
10

help_text (str)
Help-text for field, metadata purposes.
11

verbose_name (str)
Verbose name for field, metadata purposes.

Field类的子类映射到各种数据库中对应的数据类型，比如SQLite、PostgreSQL、MySQL等。

数字字段(Numeric Field)类

Peewee 中的数字字段类如下所示：

Sr.No Field classes & Description
1 IntegerField
Field class for storing integers.
2

BigIntegerField
Field class for storing big integers (maps to integer, bigint, and bigint type in SQLite, PostegreSQL and MySQL respectively).
3

SmallIntegerField
Field class for storing small integers (if supported by database).
4

FloatField
Field class for storing floating-point numbers corresponds to real data types.
5

DoubleField
Field class for storing double-precision floating-point numbers maps to equivalent data types in corresponding SQL databases.
6

DecimalField
Field class for storing decimal numbers. The parameters are mentioned below

  • max_digits (int) Maximum digits to store.

  • decimal_places (int) Maximum precision.

  • auto_round (bool) Automatically round values.

文本字段(Text fields)

Peewee 中可用的文本字段如下：

Sr.No Fields & Description
1 CharField
Field class for storing strings. Max 255 characters. Equivalent SQL data type is varchar.
2

FixedCharField
Field class for storing fixed-length strings.
3

TextField
Field class for storing text. Maps to TEXT data type in SQLite and PostgreSQL, and longtext in MySQL.

二进制字段

Peewee 中的二进制字段描述如下：

Sr.No Fields & Description
1 BlobField
Field class for storing binary data.
2

BitField
Field class for storing options in a 64-bit integer column.
3

BigBitField
Field class for storing arbitrarily-large bitmaps in a Binary Large OBject (BLOB). The field will grow the underlying buffer as necessary.
4

UUIDField
Field class for storing universally unique identifier (UUID) objects. Maps to UUID type in Postgres. SQLite and MySQL do not have a UUID type, it is stored as a VARCHAR.

日期和时间字段

Peewee 中的日期和时间字段如下 –

Sr.No Fields & Description
1 DateTimeField
Field class for storing datetime.datetime objects. Accepts a special parameter string formats, with which the datetime can be encoded.
2

DateField
Field class for storing datetime.date objects. Accepts a special parameter string formats to encode date.
3

TimeField
Field class for storing datetime.time objectsAccepts a special parameter formats to show encoded time.

由于 SQLite 没有 DateTime 数据类型，因此该字段被映射为字符串。

外键字段(ForeignKeyField )

此类用于在两个模型中建立外键关系，从而建立数据库相应的表。此类使用以下参数实例化 :

Sr.No Fields & Description
1 model (Model)
Model to reference. If set to ‘self’, it is a self-referential foreign key.
2

field (Field)
Field to reference on model (default is primary key).
3

backref (str)
Accessor name for back-reference. “+” disables the back-reference accessor.
4

on_delete (str)
ON DELETE action.
5

on_update (str)
ON UPDATE action.
6

lazy_load (bool)
Fetch the related object, when the foreign-key field attribute is accessed. If FALSE, accessing the foreign-key field will return the value stored in the foreign-key column.

外键字段示例

from peewee import *

db = SqliteDatabase('mydatabase.db')
class Customer(Model):
   id=IntegerField(primary_key=True)
   name = TextField()
   address = TextField()
   phone = IntegerField()
   class Meta:
      database=db
      db_table='Customers'

class Invoice(Model):
   id=IntegerField(primary_key=True)
   invno=IntegerField()
   amount=IntegerField()
   custid=ForeignKeyField(Customer, backref='Invoices')
   class Meta:
      database=db
      db_table='Invoices'

db.create_tables([Customer, Invoice])

执行上述脚本时，将运行以下 SQL 语句查询 –

CREATE TABLE Customers (
   id INTEGER NOT NULL
   PRIMARY KEY,
   name TEXT NOT NULL,
   address TEXT NOT NULL,
   phone INTEGER NOT NULL
);
CREATE TABLE Invoices (
   id INTEGER NOT NULL
   PRIMARY KEY,
   invno INTEGER NOT NULL,
   amount INTEGER NOT NULL,
   custid_id INTEGER NOT NULL,
   FOREIGN KEY (
      custid_id
   )
   REFERENCES Customers (id)
);

SQLiteStudio GUI 工具中验证, 表结构如下：

Peewee字段类

其他字段类型

Peewee 中的其他字段类型包括 –

Sr.No Fields & Description
1 IPField
Field class for storing IPv4 addresses efficiently (as integers).
2

BooleanField
Field class for storing boolean values.
3

AutoField
Field class for storing auto-incrementing primary keys.
4

IdentityField
Field class for storing auto-incrementing primary keys using the new Postgres 10 IDENTITYField class for storing auto-incrementing primary keys using the new Postgres 10 IDENTITY column type. column type.

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