import os
if os.path.exists('sampleDB.db'):
  os.remove('sampleDB.db')
# 引入peewee包的所有內(nèi)容
from peewee import *
# 建立一個(gè)Sqlite數(shù)據(jù)庫(kù)引擎對(duì)象，該引擎打開(kāi)數(shù)據(jù)庫(kù)文件sampleDB.db
db = SqliteDatabase("sampleDB.db")
# 定義一個(gè)ORM的基類，在基類中指定本ORM所使用的數(shù)據(jù)庫(kù)，
# 這樣在之后所有的子類中就不用重復(fù)聲明數(shù)據(jù)庫(kù)
class BaseModel(Model):
  class Meta:
    database = db
# 定義course表，繼承自BaseModel
class Course(BaseModel):
  id = PrimaryKeyField() # 定義主鍵
  title = CharField(null=False) # 定義字符串
  period = IntegerField() # 整型
  description = CharField()
  class Meta:
    order_by = ('title',)
    db_table = 'course'  # 定義數(shù)據(jù)庫(kù)中的表名
# 定義 teacher 表，繼承自BaseModel
class Teacher(BaseModel):
  id = PrimaryKeyField()
  name = CharField(null=False)
  gender = BooleanField() # 布爾型
  address = CharField()
  # ForeignKeyField 設(shè)置與course的連接關(guān)系，其中的參數(shù)：to_field用于指定被連接的字段名，related_name參數(shù)對(duì)該關(guān)系賦予了一個(gè)名字
  course_id = ForeignKeyField(Course, to_field="id", related_name="course")
  class Meta:
    order_by = ('name',)
    db_table = "teacher"
# 建表，僅需創(chuàng)建一次
Course.create_table()
Teacher.create_table()
# 新增行
Course.create(id=1, title='經(jīng)濟(jì)學(xué)', period=320, description='文理科學(xué)生均可選修')
Course.create(id=2, title='大學(xué)英語(yǔ)', period=300, description='大一學(xué)生必修課')
Course.create(id=3, title='哲學(xué)', period=100, description='必修課')
Course.create(id=134, title='編譯原理', period=100, description='計(jì)算機(jī)系選修')
Teacher.create(name='白陣君', gender=True, address='..', course_id=1)
Teacher.create(name='李森', gender=True, address='..', course_id=3)
Teacher.create(name='張?chǎng)?, gender=False, address='..', course_id=2)
# 查詢一行
record = Course.get(Course.title == '大學(xué)英語(yǔ)')
print("課程：%s, 學(xué)時(shí)：%d, 課程類型: %s" % (record.title, record.period, record.description))
# 更新
record.period = 200
record.save()
# 刪除
record.delete_instance()
# 查詢所有記錄
courses = Course.select()
for i in courses:
  print(i.id, i.title, i.period, i.description)
# 帶條件查詢，并將結(jié)果按period字段倒序排序
courses = Course.select().where(Course.id< 10).order_by(Course.period.desc())
for i in courses:
  print(i.id, i.title, i.period, i.description)
# 統(tǒng)計(jì)所有課程的平均學(xué)時(shí)
total = Course.select(fn.Avg (Course.period).alias('avg_period'))
for i in total:
  print(u"平均學(xué)時(shí)：", i.avg_period)
# 更新多個(gè)記錄
Course.update(period=300).where(Course.id > 100).execute()
# 多表連接操作，Peewee會(huì)自動(dòng)根據(jù)ForeignKeyField的外鍵定義進(jìn)行連接：
Record = Course.select().join(Teacher).where(Teacher.gender == True)
for i in Record:
  print(i.id, i.title, i.period, i.description)