Python-SQLALchemy

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官方文档

Initialization

from sqlalchemy import Integer, ForeignKey, String, Column
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship

Base = declarative_base()

class User(Base):
    __tablename__ = 'user'
    id = Column(Integer, primary_key=True)
    name = Column(String)

    addresses = relationship("Address", backref="user")

class Address(Base):
    __tablename__ = 'address'
    id = Column(Integer, primary_key=True)
    email = Column(String)
    user_id = Column(Integer, ForeignKey('user.id'))

The above configuration establishes a collection of Address objects on User called

rom sqlalchemy import Integer, ForeignKey, String, Column
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship

Base = declarative_base()

class User(Base):
    __tablename__ = 'user'
    id = Column(Integer, primary_key=True)
    name = Column(String)

    addresses = relationship("Address", back_populates="user")
        
class Address(Base):
    __tablename__ = 'address'
    id = Column(Integer, primary_key=True)
    email = Column(String)
    user_id = Column(Integer, ForeignKey('user.id'))

    user = relationship("User", back_populates="addresses")

Above, we add a .user relationship to Address explicitly. On both relationships, the

>>> u1 = User()
>>> a1 = Address()
>>> u1.addresses
[]
>>> print(a1.user)
None

However, once the Address is appended to the u1.addresses collection, both the collection and the scalar attribute have been populated:

>>> u1.addresses.append(a1)
>>> u1.addresses
[<__main__.address object at>]
>>> a1.user
<__main__.user object at></__main__.user></__main__.address>

This behavior of course works in reverse for removal operations as well, as well as for equivalent operations on both sides. Such as when .user is set again to None, the Address object is removed from the reverse collection:

>>> a1.user = None
>>> u1.addresses
[]

The manipulation of the .addresses collection and the .user attribute occurs entirely in Python without any interaction with the SQL database. Without this behavior, the proper state would be apparent on both sides once the data has been flushed to the database, and later reloaded after a commit or expiration operation occurs. The backref/back_populates behavior has the advantage that common bidirectional operations can reflect the correct state without requiring a database round trip.

Remember, when the backref keyword is used on a single relationship, it’s exactly the same as if the above two relationships were created individually using back_populates on each.

mysql操作

检验一下我们上面的成果以及

from sqlalchemy import Column, String, Integer, create_engine, SmallInteger
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base

DB_URI = 'sqlite:///user.db'
Base = declarative_base()
engine = create_engine(DB_URI)
Base.metadata.bind = engine
Session = sessionmaker(bind=engine)
session = Session()

class User(Base):
    __tablename__ = 'live_user'
    
    id = Column(Integer, unique=True, primary_key=True, autoincrement=True)
    speaker_id = Column(String(40), index=True, unique=True)
    name = Column(String(40), index=True, nullable=False)
    gender = Column(SmallInteger, default=2)
    headline = Column(String(200))
    avatar_url = Column(String(100), nullable=False)
    bio = Column(String(200))
    description = Column(String())
    
    @classmethod
    def add(cls, **kwargs):
        speaker_id = kwargs.get('speaker_id', None)
        if id is not None:
            r = session.query(cls).filter_by(speaker_id=speaker_id).first()
            if r:
                return r
        try:
            r = cls(**kwargs)
            session.add(r)
            session.commit()
        except:
            session.rollback()
            raise
        else:
            return r

Base.metadata.create_all()

接口分为2种：

1. https://api.zhihu.com/lives/o... (未结束)

2. https://api.zhihu.com/lives/e... (已结束)

elasticsearch-dsl-py相比elasticsearch-py做了各种封装，DSL也支持用类代表一个doc_type（类似数据库中的Table），实现ORM的效果。我们就用它来写Live模型：

from elasticsearch_dsl import DocType, Date, Integer, Text, Float, Boolean
from elasticsearch_dsl.connections import connections
from elasticsearch_dsl.query import SF, Q
from config import SEARCH_FIELDS
from .speaker import User, session

connections.create_connection(hosts=['localhost'])

In : from elasticsearch_dsl.query import Q
In : Q('multi_match', subject='python').to_dict()
Out: {'multi_match': {'subject': 'python'}}

In : from elasticsearch import Elasticsearch
In : from elasticsearch_dsl import Search, Q
In : s = Search(using=client, index='live')
In : s = s.query('match', subject='python').query(~Q('match', description='量化'))
In : s.execute()
Out: <response:>]></response:>

上述例子表示从live这个索引（类似数据库中的Database）中找到subject字典包含python，但是description字段不包含量化的Live。

今天带大家了解了MySQL、python、sqlalchemy的相关知识，希望对你有所帮助；关于数据库的技术知识我们会一点点深入介绍，欢迎大家关注golang学习网公众号，一起学习编程~