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Python flaskalchemy 笔记(极致简化版)_engine_from_config

作者：我家自动化 | 2024-03-02 14:30:27

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engine_from_config

文章目录

- Core Tutorial
- ORM Tutorial

Core Tutorial

版本检查

import sqlalchemy
print(sqlalchemy.__version__)
print(dir(sqlalchemy))
# BINARY | LargeBinary | VARBINARY | SMALLINT | SamllInteger | INT | INTEGER | Integer | BIGINT | BigInteger
# DECIMAL | FLOAT | Float | NUMERIC | Numeric | REAL
# CHAR | NCHAR | VARCHAR | NVARCHAR | CLOB | BLOB | TEXT | Text | String
# BOOLEAN | Boolean
# DATE | TIME | DATETIME | DDL | TIMESTAMP | Date | Time | DateTime
# Enum | Sequence | ARRAY | JSON
# Constraint | PrimaryKeyConstraint | ForeignKey | ForeignKeyConstraint | Index | CheckConstraint | UniqueConstraint
# BLANK_SCHEMA | Column | ColumnDefault | DefaultClause | FetchedValue | Interval | MetaData | ThreadLocalMetaData | Table | TypeDecorator | PassiveDefault | PickleType | Unicode | UnicodeText
# 建表相关: column | table | tablesample(相当于view把) | collate
# 语句类型: delete | update | select | subquery | insert
# distinct
# 多表连接: join | outerjoin | alias(相当于as)
# where后的: all_ | any_ | exists | and_ | or_ | not_ | between | true | false | null | nullsfirst(排序时为null的记录放顶部，mysql不支持null first|last语法) | nullslast | bindparam | case | within_group
# 多条查询: (并集) union | (有all的包含重复列) union_all | (差集，即第一表有第二表无的，mysql不支持) except_ | except_all | (交集) intersect | intersect_all
# order by后的: asc | desc
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# 异常模块: exc
# 引擎模块: engine | engine_from_config | create_engine
# 工具模块: util | cutils
# 连接池模块: pool
# schema模块: schema
# 语句模块: sql
# func功能: func | funcfilter
# processors: processors | cprocessors
# event: event | events
# inspection: inspection | inspect
# cresultproxy: cresultproxy
# dialects: dialects
# log: log
# types: types
# interfaces: interfaces
# ['cast', 'extract', 'lateral', 'literal', 'literal_column', 'modifier', 'outparam', 'over', 'text', 'tuple_', 'type_coerce']
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连接

示例

sqlite3_engine = sqlalchemy.create_engine('sqlite:///:memory', echo=True, encoding='UTF-8')
# mysql-python(python2中的mysqldb): mysql+mysqldb://<user>:<password>@<host>[:<port>]/<dbname>
# pymysql: mysql+pymysql://<username>:<password>@<host>/<dbname>[?<options>]
# mysql-connector: mysql+mysqlconnector://<user>:<password>@<host>[:<port>]/<dbname>
# cx_oracle: oracle+cx_oracle://user:pass@host:port/dbname[?key=value&key=value...]
# http://docs.sqlalchemy.org/en/latest/dialects/index.html
print(dir(sqlite3_engine))
# sqlite3_engine.url: 'sqlite:///:memory'
# sqlite3_engine.driver: 'pysqlite'
# sqlite3_engine.echo: True
# sqlite3_engine.name: 'sqlite'
# transaction = sqlite3_engine.begin()
# connection = sqlite3_engine.connect(**args)
# sqlite3_engine.dialect  # <sqlalchemy.dialects.sqlite.pysqlite.SQLiteDialect_pysqlite at 0x217dc71a080>
# sqlite3_engine.dispose()  # 关闭了engine，还在执行的connection也会失去关联，但那些connection执行完后也会自动被回收
# sqlite3_engine.execute(stat, *multiparams, **params)
# shard1 = sqlite3_engine.execution_options(shard_id='shard1')  # 生成具有 shard_id='shard1' 执行选项的 engine
    # from sqlalchemy import event
    # from sqlalchemy.engine import Engine
    # shards = {"default": "base", shard_1: "db1", "shard_2": "db2"}
    # @event.listens_for(Engine, "before_cursor_execute")
    # def _switch_shard(conn, cursor, stmt, params, context, executemany):
    #     shard_id = conn._execution_options.get('shard_id', "default")
    #     current_shard = conn.info.get("current_shard", None)
    #     if current_shard != shard_id:
    #         cursor.execute("use %s" % shards[shard_id])
    #         conn.info["current_shard"] = shard_id
# shard1.get_execution_options()
# shard1.update_execution_options(**opt)
# sqlite3_engine.has_table(table_name, schema=None)
# sqlite3_engine.table_names(schema=None, connection=None)
# sqlite3_engine.logging_name  # 空的
# sqlite3_engine.logger  # <sqlalchemy.log.InstanceLogger at 0x217dd8c5048>
# ['dispatch', 'engine', 'pool', 'raw_connection', 'run_callable', 'scalar', 'schema_for_object', 'transaction']
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postgresql

# default
engine = create_engine('postgresql://scott:tiger@localhost/mydatabase')
# psycopg2
engine = create_engine('postgresql+psycopg2://scott:tiger@localhost/mydatabase')
# pg8000
engine = create_engine('postgresql+pg8000://scott:tiger@localhost/mydatabase')
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mysql

# default
engine = create_engine('mysql://scott:tiger@localhost/foo')
# mysqlclient (a maintained fork of MySQL-Python)
engine = create_engine('mysql+mysqldb://scott:tiger@localhost/foo')
# PyMySQL
engine = create_engine('mysql+pymysql://scott:tiger@localhost/foo')
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oracle

engine = create_engine('oracle://scott:tiger@127.0.0.1:1521/sidname')
engine = create_engine('oracle+cx_oracle://scott:tiger@tnsname')
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microsoft sql server

# pyodbc
engine = create_engine('mssql+pyodbc://scott:tiger@mydsn')
# pymssql
engine = create_engine('mssql+pymssql://scott:tiger@hostname:port/dbname')
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sqlite

# sqlite://<nohostname>/<path>
# where <path> is relative:
engine = create_engine('sqlite:///foo.db')
# Unix/Mac - 4 initial slashes in total
engine = create_engine('sqlite:absolute/path/to/foo.db')
# Windows
engine = create_engine('sqlite:///C:\\path\\to\\foo.db')
# Windows alternative using raw string
engine = create_engine(r'sqlite:///C:\path\to\foo.db')
engine = create_engine('sqlite://')
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sqlalchemy.engine_from_config(configuration, prefix=‘sqlalchemy.’, **kwargs)
sqlalchemy.engine.url.make_url(name_or_url) # class sqlalchemy.engine.url.URL(drivername, username=None, password=None, host=None, port=None, database=None, query=None)
1. url.get_dialect()
2. url.translate_connect_args(names=[], **kw)

建表

from sqlalchemy import Table, Column, Integer, String, MetaData, ForeignKey
metadata = MetaData()
users = Table('users', metadata, Column('id', Integer, primary_key=True), Column('name', String), Column('fullname', String))
addresses = Table('addresses', metadata, Column('id', Integer, primary_key=True), Column('user_id', None, ForeignKey('users.id')), Column('email_address', String, nullable=True))
metadata.create_all(sqlite3_engine)
print(dir(users))
# ['__and__', '__bool__', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getstate__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__invert__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__nonzero__', '__or__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__visit_name__', '__weakref__', '_annotate', '_annotations', '_autoincrement_column', '_autoload', '_clone', '_cloned_set', '_cols_populated', '_columns', '_compiler', '_compiler_dispatch', '_constructor', '_copy_internals', '_deannotate', '_execute_on_connection', '_extra_dependencies', '_extra_kwargs', '_from_objects', '_hide_froms', '_init', '_init_collections', '_init_existing', '_init_items', '_is_clone_of', '_is_from_container', '_is_join', '_is_lateral', '_is_lexical_equivalent', '_is_select', '_kw_reg_for_dialect', '_kw_reg_for_dialect_cls', '_kw_registry', '_memoized_property', '_negate', '_order_by_label_element', '_params', '_populate_column_collection', '_prefixes', '_refresh_for_new_column', '_reset_exported', '_schema_item_copy', '_select_iterable', '_set_parent', '_set_parent_with_dispatch', '_sorted_constraints', '_textual', '_translate_schema', '_validate_dialect_kwargs', '_with_annotations', 'add_is_dependent_on', 'alias', 'append_column', 'append_constraint', 'append_ddl_listener', 'argument_for', 'bind', 'c', 'columns', 'comment', 'compare', 'compile', 'constraints', 'correspond_on_equivalents', 'corresponding_column', 'count', 'create', 'delete', 'description', 'dialect_kwargs', 'dialect_options', 'dispatch', 'drop', 'exists', 'foreign_key_constraints', 'foreign_keys', 'fullname', 'get_children', 'implicit_returning', 'indexes', 'info', 'insert', 'is_clause_element', 'is_derived_from', 'is_selectable', 'join', 'key', 'kwargs', 'lateral', 'metadata', 'name', 'named_with_column', 'outerjoin', 'params', 'primary_key', 'quote', 'quote_schema', 'replace_selectable', 'schema', 'select', 'selectable', 'self_group', 'supports_execution', 'tablesample', 'tometadata', 'unique_params', 'update']
# 主要的有 insert/select/update/delete
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插入

ins = users.insert()
print(ins)  # 'INSERT INTO users (id, name, fullname) VALUES (:id, :name, :fullname)'
ins = users.insert().values(name='jack', fullname='Jack Jones')
print(ins)  # 'INSERT INTO users (name, fullname) VALUES (:name, :fullname)'
print(ins.compile().params)  # {'fullname': 'Jack Jones', 'name': 'jack'}
# insert | update | delete
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执行

conn = sqlite3_engine.connect()
result = conn.execute(ins)
ins.bind = engine
print(ins)  # 'INSERT INTO users (name, fullname) VALUES (?, ?)'
print(result.inserted_primary_key)  # 1
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执行多条语句

ins = users.insert()
result = conn.execute(ins, id=2, name='wendy', fullname='Wendy Williams')
results = conn.execute(addresses.insert(), [
    {'user_id': 1, 'email_address': 'jack@yahoo.com'}
    {'user_id': 1, 'email_address': 'jack@msn.com'}
    {'user_id': 2, 'email_address': 'www@www.org'}
    {'user_id': 2, 'email_address': 'wendy@aol.com'}
])
# executemany这样的形式可以用于 select | update | delete
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查询

from sqlalchemy.sql import select
sel = select([users])
result = conn.execute(sel)
for row in result:
    print(row)
result.close()
result = conn.execute(sel)
row = result.fetchone()
# rows = result.fetchall()
print("name:", row['name'], "; fullname:", row['fullname'])
print("name:", row[1], "; fullname:", row[2])
print("name:", row[users.c.name], "; fullname:", row[users.c.fullname])
result.close()
for row in conn.execute(select([users, addresses])):
    print(row)
s = select([users, addresses]).where(users.c.id == addresses.c.user_id)
for row in conn.execute(s):
    print(row)
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Operators https://docs.sqlalchemy.org/en/13/core/tutorial.html#operators

print(users.c.id == addresses.c.user_id)  # users.id = addresses.user_id
print(users.c.id == 7)  # users.id = :id_1
print((users.c.id == 7).compile().params)  # {u'id_1': 7}
print(users.c.id != 7)  # users.id != :id_1
print(users.c.name == None)  # users.name IS NULL
print('fred' > users.c.name)  # users.name < :name_1
print(users.c.id + addresses.c.id)  # users.id + addresses.id
print(users.c.name + users.c.fullname)  # users.name || users.fullname
print((users.c.name + users.c.fullname).compile(bind=create_engine('mysql://')))  # concat(users.name, users.fullname)
print(users.c.name.op('tiddlywinks')('foo'))  # users.name tiddlywinks :name_1
print(somecolumn.op('&')(0xff))  # 
from sqlalchemy import type_coerce
expr = type_coerce(somecolumn.op('-%>')('foo'), MySpecialType())
stmt = select([expr])
somecolumn.bool_op('-->')('some value')
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连接

from sqlalchemy.sql import and_, or_, not_
print(and_(
    users.c.name.like('j%'),
    users.c.id == addresses.c.user_id,
    or_(
        addresses.c.email_address == 'wendy@aol.com',
        addresses.c.email_address == 'jack@yahoo.com'
    ),
    not_(users.c.id > 5)
))
# users.name LIKE :name_1 AND users.id = addresses.user_id AND (addresses.email_address = :email_address_1 OR addresses.email_address = :email_address_2) AND users.id <= :id_1
print(users.c.name.like('j%') & (users.c.id == addresses.c.user_id) & ((addresses.c.email_address == 'wendy@aol.com') | (addresses.c.email_address == 'jack@yahoo.com')) & ~(users.c.id>5))  # 与上面等价，但格式太混乱
s = select(
    [(users.c.fullname + ', ' + addresses.c.email_address).label('title')]. \
    where(and_(
        users.c.id == addresses.c.user_id,
        users.c.name.between('m', 'z'),
        or_(
            addresses.c.email_address.like('%@aol.com'),
            addresses.c.email_address.like('%@msn.com')
))))
rows = conn.execute(s).fetchall()
s = select(
    [(users.c.fullname + ', ' + addresses.c.email_address).label('title')]. \
    where(users.c.id == addresses.c.user_id). \
    where(users.c.name.between('m', 'z')). \
    where(or_(
        addresses.c.email_address.like('%@aol.com'),
        addresses.c.email_address.like('%@msn.com')
)))  # 与上面等价
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textual sql https://docs.sqlalchemy.org/en/13/core/tutorial.html#using-textual-sql

from sqlalchemy.sql import text
s = text('select concat(users.fullname, ", ", addresses.email_address) as title from users, addresses where users.id=addresses.user_id and users.name between :x and :y and (addresses.email_address like :e1 or addresses.email_address like :e2)')
conn.execute(s, x='m', y='z', e1='%@aol.com', e2='%@msn.com').fetchall()
# -------- 定制参数
s = text("select * from users where users.name between :x and :y")
s = s.bindparmas(x='m', y='z'); conn.execute(s)  # or
s = s..bindparams(bindparam("x", type_=String), bindparam("y", type_=String)); conn.execute(s, {'x': 'm', 'y': 'z'})  # 定制获取的参数的类型
# ---------- 定制返回类型
s = s.columns(id=Integer, name=String)  # or
s = text("select name, id from users"); s = s.columns(users.c.id, users.c.name)  # or
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ORM Tutorial

API

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, func, ForeignKey, exists
from sqlalchemy.orm import sessionmaker, aliased, relationship
Base = declarative_base()
class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    fullname = Column(String)
    nickname = Column(String)
print(User.__table__)
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)  # Session.config(bind=engie)
session = Session()
session.add(User(name='ed', fullname='Ed Jones', nickname='edsnickname'))
session.add_all([
    User(name='wendy', fullname='Wendy Williams', nickname='windy'),
    User(name='mary', fullname='Mary Contrary', nickname='mary'),
    User(name='fred', fullname='Fred Flintstone', nickname='freddy')
])
our_user = session.query(User).filter_by(name='ed').first()
query = session.query(User).filter(User.name.in_(['Edwardo', 'fakeuser']))
for row in session.query(User).order_by(User.id):
    print(row.name, row.fullname)
for name, fullname in session.query(User.name, User.fullname):
    print(name, fullname)
for row in session.query(User, User.name, User.name.label('name_label')).all():
    print(row.User, row.name, row.name_label)
user_alias = aliased(User, name='user_alias')
for row in session.query(user_alias, user_alias.name).all():
    print(row.user_alias)
query.all()
query.first()
query.one()
query.one_or_none()
query.scalar()
query.count()
session.query(func.count(User.name), User.name).group_by(User.name).all()  # [(1, u'ed'), (1, u'fred'), (1, u'mary'), (1, u'wendy')]
session.query(func.count('*')).select_from(User).scalar()  # 4
session.query(func.count(User.id)).scalar()  # 4
our_user.nickname = 'eddie'
print(session.dirty)
print(session.new)
session.commit()
session.rollback()
fake_user in session  # False
class Address(Base):
    __tablename__ = 'addresses'
    id = Column(Integer, primary_key=True)
    email_address = Column(String(50), nullable=False)
    user_id = Column(Integer, ForeignKey('users.id'))
    user = relationship('User', back_populates='addresses')  # 相当于一个关联的User实例
    def __repr__(self):
        return '<Address(email_address="%s")>' % self.email_address
User.addresses = relationship('Address', order_by=Address.id, back_populates='users')  # 相当于一个关联的Address实例
Base.metadata.create_all(engine)
query.join(Address).filter(...)
query.outerjoin(User.addresses).filter(...)
stmt = session.query(Address.user_id, func.count('*').label('address_count')).group_by(Address.user_id).subquery()
result = session.query(User, stmt.c.address_count).outerjoin(stmt, User.id==stmt.c.user_id).order_by(User.id)
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创建映射和表

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, CHAR, VARCHAR, Enum, TIMESTAMP
Base = declarative_base()
class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    fullname = Column(String)
    nickname = Column(String)
    test1 = Column(CHAR(20))
    test2 = Column(VARCHAR(20))
    test3 = Column('test3', Enum('item1', 'item2'))
    test4 = Column('test4', TIMESTAMP)
    def __repr__(self):  # 此方法 可选，不一定需要实现
        return "<User(name='%s', fullname='%s', nickname='%s')>" % (self.name, self.fullname, self.nickname)
print(User.__table__)  # Table('users', MetaData(bind=None), Column('id', Integer(), table=<users>, primary_key=True, nullable=False), Column('name', String(), table=<users>), Column('fullname', String(), table=<users>), Column('nickname', String(), table=<users>), schema=None)
Base.metadata.create_all(engine)
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创建实例

ed_user = User(name='ed', fullname='Ed Jones', nickname='edsnickname')
print(ed_user.name, ed_user.fullname, ed_user.nickname, ed_user.id)  # 'ed' 'Ed Jones' 'edsnickname' None
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创建会话

from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind=engine)
# Session = sessionmaker()  # 如果还没有定义engine，后面可以用 Session.config(bind=engine)
session = Session()
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添加和更新对象

session.add(ed_user)  # 现在还不会提交到数据库中，先缓存起来，但如果有query操作，会立刻提交到数据库
our_user = session.query(User).filter_by(name='ed').first()
print(ed_user is our_user)  # True
session.add_all([
    User(name='wendy', fullname='Wendy Williams', nickname='windy'),
    User(name='mary', fullname='Mary Contrary', nickname='mary'),
    User(name='fred', fullname='Fred Flintstone', nickname='freddy')
])
ed_user.nickname = 'eddie'
print(session.dirty)  # IdentitySet([<User(name='ed', fullname='Ed Jones', nickname='eddie')>])
print(session.new)  # IdentitySet([<User(name='wendy', fullname='Wendy Williams', nickname='windy')>, <User(name='mary', fullname='Mary Contrary', nickname='mary')>, <User(name='fred', fullname='Fred Flintstone', nickname='freddy')>])
session.commit()
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回滚

ed_user.name = 'Edwardo'
fake_user = User(name='fakeuser', fullname='Invalid', nickname='12345')
session.add(fake_user)
session.query(User).filter(User.name.in_(['Edwardo', 'fakeuser'])).all()  # [<User(name='Edwardo', fullname='Ed Jones', nickname='eddie')>, <User(name='fakeuser', fullname='Invalid', nickname='12345')>]
session.rollback()
ed_user.name  # u'ed'
fake_user in session  # False
session.query(User).filter(User.name.in_(['ed', 'fakeuser'])).all()  # [<User(name='ed', fullname='Ed Jones', nickname='eddie')>]
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查询

基础查询

for instance in session.query(User).order_by(User.id):
    print(instance.name, instance.fullname)
# ed Ed Jones
# wendy Wendy Williams
# mary Mary Contrary
# fred Fred Flintstone
for name, fullname in session.query(User.name, User.fullname):
    print(name, fullname)
for row in session.query(User, User.name, User.name.label('name_label')).all():
    print(row.User, row.name, row.name_label)
from sqlalchemy.orm import aliased
user_alias = aliased(User, name='user_alias')
for row in session.query(user_alias, user_alias.name).all():
    print(row.user_alias)
# <User(name='ed', fullname='Ed Jones', nickname='eddie')>
# <User(name='wendy', fullname='Wendy Williams', nickname='windy')>
# <User(name='mary', fullname='Mary Contrary', nickname='mary')>
# <User(name='fred', fullname='Fred Flintstone', nickname='freddy')>
# filter可以接受比filter_by更灵活的SQL表达式语言结构
for name, in session.query(User.name).filter_by(fullname='Ed Jones'): pass
for name, in session.query(User.name).filter(User.fillname=='Ed Jones'): pass
# limit与offset可以使用python的切分或者 limit与offset 方法
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filter()方法常用语句

query.filter(User.name == 'ed')  # equals
query.filter(User.name != 'ed')  # not equals
query.filter(User.name.like('%ed%'))  # like
query.filter(User.name.ilike('%ed%'))  # like(不区分大小写)
query.filter(User.name.in_(['ed', 'wendy', 'jack']))  # in
query.filter(User.name.in_(session.query(User.name).filter(User.name.like('%ed%'))))  # in subquery
query.filter(~User.name.in_(['ed', 'wendy', 'jack']))  # not in
query.filter(User.name == None)  # is NULL  或者  query.filter(User.name.is_(None))
query.filter(User.name != None)  # is not NULL  或者  query.filter(User.name.isnot(None))
from sqlalchemy import and_, or_, not_
query.filter(and_(User.name == 'ed', User.fullname == 'Ed Jones'))  # and  或者  query.filter(User.name == 'ed', User.fullname == 'Ed Jones')  或者  query.filter(User.name == 'ed').filter(User.fullname == 'Ed Jones')
query.filter(or_(User.name == 'ed', User.fullname == 'Ed Jones'))  # or
query.filter(User.name.match('wendy'))  # match
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query = session.query(User).filter(User.name.like('%ed')).order_by(User.id)
query.all()  # 返回列表
query.first()
query.one()  # 如果有多行或者找不到则报错
query.one_or_none()  # 多结果时报错，否则返回但结果或者None
query.scalar()  # 调用one方法，并在成功时返回该行的第一列
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使用文本sql

from sqlalchemy import text
for user in session.query(User).filter(text('id < 224')).order_by(text('id')).all():
    print(user)
session.query(User).filter(text('id < :value and name = :name')).params(value=224, name='fred').order_by(User.id).one()
session.query(User).from_statement(text('select * from users where name = :name')).parmas(name='ed').all()  # 要使用sql语句，需要使用from_statement
stmt = text('select name, id, fullname, nickname from users where name = :name')
stmt = stmt.columns(User.name, User.id, User.fullname, User.nickname)  # 绑定返回类型，结果返回User
session.query(User).from_statement(stmt).params(name='ed').all()  # [<User(name='ed', fullname='Ed Jones', nickname='eddie')>]
stmt = text('select name, id from users where name = :name')
stmt = stmt.columns(User.name, User.id)  # 绑定返回类型
session.query(User.id, User.name).from_statement(stmt).params(name='ed').all()  # [(1, u'ed')]
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计数

query.count()
from sqlalchemy import func
session.query(func.count(User.name), User.name).group_by(User.name).all()  # [(1, u'ed'), (1, u'fred'), (1, u'mary'), (1, u'wendy')]
session.query(func.count('*')).select_from(User).scalar()  # 4
session.query(func.count(User.id)).scalar()  # 4
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建立关系

from sqlalchemy import ForeignKey
from sqlalchemy.orm import relationship
class Address(Base):
    __tablename__ = 'addresses'
    id = Column(Integer, primary_key=True)
    email_address = Column(String(50), nullable=False)
    user_id = Column(Integer, ForeignKey('users.id'))
    user = relationship('User', back_populates='addresses')  # 相当于一个关联的User实例
    def __repr__(self):
        return '<Address(email_address="%s")>' % self.email_address
User.addresses = relationship('Address', order_by=Address.id, back_populates='users')  # 相当于一系列关联的Address实例
Base.metadata.create_all(engine)
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使用相关对象

jack = User(name='jack', fullname='Jack Bean', nickname='gjffdd')
jack.addresses  # 默认是[]
jack.addresses = [Address(email_address='jack@google.com'), Address(email_address='j25@yahoo.com')]
jack.addresses[1]  # <Address(email_address='j25@yahoo.com')>
jack.addresses[1].user  # <User(name='jack', fullname='Jack Bean', nickname='gjffdd')>
session.add(jack)
session.commit()
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join查询

基础join

for u, a in session.query(User, Address).filter(User.id==Address.user_id).filter(Address.email_address=='jack@google.com').all():
    print(u, a, sep='\n')
# <User(name='jack', fullname='Jack Bean', nickname='gjffdd')>
# <Address(email_address='jack@google.com')>
for u in session.query(User).join(Address).filter(Address.email_address=='jack@google.com').all():  # 因为有foreign key，所以join知道如何关联
    print(u)
# 在没有foreign key时，可以如下:
query.join(Address, User.id==Address.user_id)
query.join(User.addresses)
query.join(Address, User.addresses)
query.join('addresses')
# 另外，还有 left outer join:
query.outerjoin(User.addresses)
# query中如果需要有多个实体
query = session.query(User, Address).select_from(Address).join(User)  # 先选择Address，然后根据key选择User
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别名

adalias1 = aliased(Address)
adalias2 = aliased(Address)
for username, email1, email2 in session.query(User.name, adalias1.email_address, adalias2.email_address). \
        join(adalias1, User.addresses).join(adalias2, User.addresses). \
        filter(adalias1.email_address=='jack@google.com').filter(adalias2.email_address=='j25@yahoo.com'):
    print(username, email1, email2)
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子查询

select users.*, adr_count.address_count from users left outer join
    (select user_id, count(*) as address_count from addresses group by user_id) as adr_count
    on users.id = adr_count.user_id
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stmt = session.query(Address.user_id, func.count('*').label('address_count')).group_by(Address.user_id).subquery()
result = session.query(User, stmt.c.address_count).outerjoin(stmt, User.id==stmt.c.user_id).order_by(User.id)
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从子查询中映射回实体

stmt = session.query(Address.user_id, func.count('*').label('address_count')).group_by(Address.user_id).subquery()
adalias1 = aliased(Address, stmt)
for user, address in session.query(User, adalias1).join(adalias1, User.addresses):
    print(user, address, sep='\t')
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使用exists

from sqlalchemy.sql import exists
stmt = exists().where(Address.user_id==User.id)
for name, in session.query(User.name).filter(stmt):
    print(name)
# 等价于
for name, in session.query(User.name).filter(User.addresses.any()):
    print(name)
# has
for name, in session.query(User.name).filter(User.addresses.any(Address.email_address.like('%google%'))):
    print(name)
# 其他
session.query(Address).filter(~Address.user.has(User.name=='jack')).all()
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常见关系运算符

query.filter(Address.user == someuser)  # many-to-one “equals” comparison
query.filter(Address.user != someuser)  # many-to-one “not equals” comparison
query.filter(Address.user == None)  # many-to-one comparison
query.filter(User.addresses.contains(someaddress))  # one-to-many
query.filter(User.addresses.any(Address.email_address == 'bar'))  # one-to-many
query.filter(User.addresses.any(email_address == 'bar'))  # one-to-many
query.filter(User.addresses.has(name == 'ed'))  # used for scalar references
session.query(Address).with_parent(someuser, 'addresses')  # used for any relationship
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急切加载

选择加载: 会发起第二次select

from sqlalchmey.orm import selectinload
jack = session.query(User).options(selectinload(User.addresses)).filter_by(name='jack').one()
print(jack, jack.addresses, sep='\n')
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连接加载: 发起left outer join

from sqlalchemy.orm import joinedload
jack = session.query(User).options(joinedload(User.addresses)).filter_by(name='jack').one()
print(jack, jack.addresses, sep='\n')
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Explicit Join + Eagerload

from sqlalchemy.orm import contains_eager
jacks_addresses = session.query(Address).join(Address.user).filter(name=='jack').options(contains_eager(Address.user)).all()
print(jacks_address[0].user, jacks_addresses, sep='\n')
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删除

session.delete(jack)
session.query(User).filter_by(name='jack').count()  # 0
session.query(Address).filter(Address.email_address.in_(['jack@google.com', 'j25@yahoo.com'])).count()  # 2
# sqlalchemy不会自己删除有外键依赖这些的对象的，需要自己来做
session.close()
Base = declarative_base()
class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    fullname = Column(String)
    nickname = Column(String)
    address = relationship('Address', back_populates='users', cascade='all, delete, delete-orphan')  # TODO，重点
    def __repr__(self):
        return "<User(name='%s', fullname='%s', nickname='%s')>" % (self.name, self.fullname, self.nickname)
class Address(Base):
    __tablename__ = 'addresses'
    id = Column(Integer, primary_key=True)
    email_address = Column(String, nullable=False)
    user_id = Column(Integer, Foreignkey('users.id'))
    user = relationship('User', back_populates='addresses')
    def __repr__(self):
        return "<Address(email_address='%s')>" % self.email_address
Base.metadata.create_all(engine)
# 可以正常删除address，不影响user
jack = session.query(User).get(5)  # get根据primary_key
del jack.addresses[1]
session.query(Address).filter(Address.email_address.in_(['jack@google.com', 'j25@yahoo.com'])).count()  # 1
# 删除user可以删除相关的addresses
session.delete(jack)
session.query(User).filter_by(name='jack').count()  # 0
session.query(Address).filter(Address.email_address.in_(['jack@google.com', 'j25@yahoo.com'])).count()  # 0
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建立多对多关系

from sqlalchemy import Table, Text
post_keywords = Table("post_keywords", Base.metadata, 
    Column('post_id', ForeignKey('posts.id'), primary_key=True),
    Column('keyword_id', ForeignKey('keywords.id'), primary_key=True)
)
class BlogPost(Base):
    __tablename__ = 'posts'
    id = Column(Integer, primary_key=True)
    user_id = Column(Integer, ForeignKey('users.id'))
    headline = Column(String(255), nullable=False)
    body = Column(Text)
    # many to many BlogPost<->Keyword
    keywords = relationship('Keyword', secondary=post_keywords, back_populates='posts')
    def __init__(self, headline, body, author):
        self.author = author
        self.headline = headline
        self.body = body
    def __repr__(self):
        return "BlogPost(%r, %r, %r)" % (self.headline, self.body, self.author)
class Keyword(Base):
    __tablename__ = 'keywords'
    id = Column(Integer, primary_key=True)
    keyword = Column(String(50), nullable=False, unique=True)
    posts = relationship('BlogPost', secondary=post_keywords, back_populates='keywords')
    def __init__(self, keyword):
        self.keyword = keyword
BlogPost.author = relationship(User, back_populates="posts")
User.posts = relationship(BlogPost, back_populates="author", lazy="dynamic")
Base.metadata.create_all(engine)
wendy = session.query(User).filter_by(name='wendy').one_or_none()  # not None
post = BlogPost("Wendy's Blog Post", "This is a test", wendy)
session.add(post)
post.keywords.append(Keyword('wendy'))
post.keywords.append(Keyword('firstpost'))
session.query(BlogPost).filter(BlogPost.keywords.any(keyword='firstpost')).all()  # [BlogPost("Wendy's Blog Post", 'This is a test', <User(name='wendy', fullname='Wendy Williams', nickname='windy')>)]
session.query(BlogPost).filter(BlogPost.author==wendy).filter(BlogPost.keywords.any(keyword='firstpost')).all()  # [BlogPost("Wendy's Blog Post", 'This is a test', <User(name='wendy', fullname='Wendy Williams', nickname='windy')>)]
wendy.posts.filter(BlogPost.keywords.any(keyword='firstpost')).all()
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进一步查考
1. Query Reference: Query API
2. Mapper Reference: Mapper Configuration
3. Relationship Reference: Relationship Configuration
4. Session Reference: Using the Session
link
- Using DATEADD in sqlalchemy
- sqlalchemy order_by

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