sqlalchemy连接postgresql

其实python的orm大多数都继承了元类（type）,sqlalchemy也不例外，想知道元类是怎么回事可以看我的另一篇文章：python __metaclass__

如果出现权限问题请把url里面的地址改为ip地址，不要用localhost

App和User里面的tablename对应数据库里面的表名

执行之前手动连一下postgresql数据库查看一下数据

from sqlalchemy import Column,String,create_engine
from sqlalchemy.types import CHAR,Integer,String,Text
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from flask import jsonify
from sqlalchemy import func
Base = declarative_base()
class App(Base):
    __tablename__ = 'app'    
    id = Column(Integer,primary_key=True)
    name = Column(String(32))
    cn_name = Column(String(32))
    desc = Column(Text)
    status = Column(Integer)
class User(Base):
    __tablename__ = 't_user'
    userid = Column('userid',Integer,primary_key=True,nullable=True)
    username = Column('username',String(64),nullable=True)
    password = Column('password',String(64),nullable=True)


engine = create_engine('postgresql://postgres:postgres@172.17.0.37:5432/skynet',echo=True)
DBsession = sessionmaker(bind=engine)
session = DBsession()
query = session.query(App)
print session.query(func.count(App.id)).one()[0]统计多少


for i in query.all():                        #列出所有
    print i.id,i.name,i.cn_name,i.desc,i.status

几种常见sqlalchemy查询：
#简单查询    
print(session.query(User).all())
print(session.query(User.name, User.fullname).all())    
print(session.query(User, User.name).all())        

#带条件查询    
print(session.query(User).filter_by(name='user1').all())    
print(session.query(User).filter(User.name == "user").all())    
print(session.query(User).filter(User.name.like("user%")).all())      

  
#多条件查询    
print(session.query(User).filter(and_(User.name.like("user%"), User.fullname.like("first%"))).all())    
print(session.query(User).filter(or_(User.name.like("user%"), User.password != None)).all())        

#sql过滤    
print(session.query(User).filter("id>:id").params(id=1).all())        

#关联查询     
print(session.query(User, Address).filter(User.id == Address.user_id).all())    
print(session.query(User).join(User.addresses).all())    
print(session.query(User).outerjoin(User.addresses).all())        

#聚合查询    
print(session.query(User.name, func.count('*').label("user_count")).group_by(User.name).all())    
print(session.query(User.name, func.sum(User.id).label("user_id_sum")).group_by(User.name).all())        

#子查询    
stmt = session.query(Address.user_id, func.count('*').label("address_count")).group_by(Address.user_id).subquery()    
print(session.query(User, stmt.c.address_count).outerjoin((stmt, User.id == stmt.c.user_id)).order_by(User.id).all())     

   
#exists    
print(session.query(User).filter(exists().where(Address.user_id == User.id)))    
print(session.query(User).filter(User.addresses.any()))

限制返回字段查询
person = session.query(Person.name, Person.created_at,Person.updated_at).filter_by(name="zhongwei").order_by(Person.created_at).first()

记录总数查询：
from sqlalchemy import func


# count User records, without
# using a subquery.
session.query(func.count(User.id))


# return count of user "id" grouped
# by "name"
session.query(func.count(User.id)).\
        group_by(User.name)


from sqlalchemy import distinct
# count distinct "name" values
session.query(func.count(distinct(User.name)))

按条件list筛选

params = list()params.append(Company.status == 1)

g.pg_db.query(Company).filter(*params).all()