peewee Field的创建

1,peewee跨表操作

1，查询tweet的所有
tweets = (Tweet
          .select(Tweet, User)
          .join(User)
          .order_by(Tweet.created_date.desc()))
for tweet in tweets:
    print(tweet.user.username, tweet.message)

2，查询倒叙的tweet

tweets = Tweet.select().order_by(Tweet.created_date.desc())
for tweet in tweets:
    # WARNING: an additional query will be issued for EACH tweet
    # to fetch the associated User data.
    print(tweet.user.username, tweet.message)

3，反向调用

class Message(Model):
    from_user = ForeignKeyField(User, backref='outbox')
    to_user = ForeignKeyField(User, backref='inbox')
    text = TextField()

for message in some_user.outbox:
    # We are iterating over all Messages whose from_user is some_user.
    print(message)

for message in some_user.inbox:
    # We are iterating over all Messages whose to_user is some_user
    print(message)

2，字段类型解析

1,datetime，time，date的field关键字
DateField has properties for:

year
month
day
TimeField has properties for:

hour
minute
second
DateTimeField has all of the above.

关于时间的查询

# Get the current time.
now = datetime.datetime.now()

# Get days that have events for the current month.
Event.select(Event.event_date.day.alias('day')).where(
    (Event.event_date.year == now.year) &
    (Event.event_date.month == now.month))

BitField

class Post(Model):

    content i= TextField()
    flags = BitField()

    is_favorite = flags.flag(1)
    is_sticky = flags.flag(2)
    is_minimized = flags.flag(4)
    is_deleted = flags.flag(8)

>>> p = Post()
>>> p.is_sticky = True
>>> p.is_minimized = True
>>> print(p.flags)  # Prints 4 | 2 --> "6"
6
>>> p.is_favorite
False
>>> p.is_sticky
True

# Generates a WHERE clause that looks like:
# WHERE (post.flags & 1 != 0)
favorites = Post.select().where(Post.is_favorite)

# Query for sticky + favorite posts:
sticky_faves = Post.select().where(Post.is_sticky & Post.is_favorite)

还可以对字段增加参数

class Bitmap(Model):
    data = BigBitField()

bitmap = Bitmap()

# Sets the ith bit, e.g. the 1st bit, the 11th bit, the 63rd, etc.
bits_to_set = (1, 11, 63, 31, 55, 48, 100, 99)
for bit_idx in bits_to_set:
    bitmap.data.set_bit(bit_idx)

# We can test whether a bit is set using "is_set":
assert bitmap.data.is_set(11)
assert not bitmap.data.is_set(12)

在Meta中，我们可以通过Meta获取相关的字段信息

from peewee import *

contacts_db = SqliteDatabase('contacts.db')

class Person(Model):
    name = CharField()

    class Meta:
        database = contacts_db

>>> Person._meta.fields
{'id': <peewee.PrimaryKeyField object at 0x7f51a2e92750>,
 'name': <peewee.CharField object at 0x7f51a2f0a510>}

>>> Person._meta.primary_key
<peewee.PrimaryKeyField object at 0x7f51a2e92750>

>>> Person._meta.database
<peewee.SqliteDatabase object at 0x7f519bff6dd0>

 Meta中的字段

database    　　　　　　database for model    yes
table_name    　　　　name of the table to store data    no
table_function    function to generate table name dynamically    yes
indexes    a list of fields to index    yes
primary_key    a CompositeKey instance    yes
constraints    a list of table constraints    yes
schema    the database schema for the model    yes
only_save_dirty    when calling model.save(), only save dirty fields    yes
options    dictionary of options for create table extensions    yes
table_settings    list of setting strings to go after close parentheses    yes
temporary    indicate temporary table    yes
legacy_table_names    use legacy table name generation (enabled by default)    yes
table_alias    an alias to use for the table in queries    no
depends_on    indicate this table depends on another for creation    no
without_rowid    indicate table should not have rowid (SQLite only)    no

 联合唯一

class BlogToTag(Model):
    """A simple "through" table for many-to-many relationship."""
    blog = ForeignKeyField(Blog)
    tag = ForeignKeyField(Tag)

    class Meta:
        primary_key = CompositeKey('blog', 'tag')

 3，字段的约束constraints

class Product(Model):
    name = CharField(unique=True)
    price = DecimalField(constraints=[Check('price < 10000')])
    created = DateTimeField(
        constraints=[SQL("DEFAULT (datetime('now'))")])

4，定制唯一索引

class Transaction(Model):
    from_acct = CharField()
    to_acct = CharField()
    amount = DecimalField()
    date = DateTimeField()

    class Meta:
        indexes = (
            # create a unique on from/to/date　　　　#是否建立唯一索引
            (('from_acct', 'to_acct', 'date'), True),

            # create a non-unique on from/to　　　　#该列数据每一个是否唯一
            (('from_acct', 'to_acct'), False),
        )

 5,定义主键是自己，自关联

class Category(Model):
    name = CharField()
    parent = ForeignKeyField('self', null=True, backref='children')

自关联查询，对自己定义别名

Parent = Category.alias()
GrandParent = Category.alias()
query = (Category
         .select(Category, Parent)
         .join(Parent, on=(Category.parent == Parent.id))
         .join(GrandParent, on=(Parent.parent == GrandParent.id))
         .where(GrandParent.name == 'some category')
         .order_by(Category.name))

6，互相关联

class User(Model):
    username = CharField()
    # Tweet has not been defined yet so use the deferred reference.
    favorite_tweet = DeferredForeignKey('Tweet', null=True)

class Tweet(Model):
    message = TextField()
    user = ForeignKeyField(User, backref='tweets')

# Now that Tweet is defined, "favorite_tweet" has been converted into
# a ForeignKeyField.
print(User.favorite_tweet)
# <ForeignKeyField: "user"."favorite_tweet">