基本使用
安装 pip3 install flask_sqlalchemy
我们在使用时候,会执行如下的代码
db = SQLAlchemy()
app = Flask(__name__)
db.init_app(app)
然后models
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, UniqueConstraint, Index,DateTime,ForeignKey
from s8day130_pro import db
class Users(db.Model):
__tablename__ = 'users'
id = Column(Integer, primary_key=True,autoincrement=True)
name = Column(String(32),nullable=False,unique=True)
然后创建表
app = create_app()
#从栈拿app
with app.app_context():
# db.drop_all()
db.create_all()
# data = db.session.query(models.Users).all()
# print(data)
另外需要配置如下:
class BaseConfig(object):
# SESSION_TYPE = 'redis' # session类型为redis
# SESSION_KEY_PREFIX = 'session:' # 保存到session中的值的前缀
# SESSION_PERMANENT = True # 如果设置为False,则关闭浏览器session就失效。
# SESSION_USE_SIGNER = False # 是否对发送到浏览器上 session:cookie值进行加密
SQLALCHEMY_DATABASE_URI = "mysql+pymysql://root:[email protected]:3306/test?charset=utf8"
SQLALCHEMY_POOL_SIZE = 5
SQLALCHEMY_POOL_TIMEOUT = 30
SQLALCHEMY_POOL_RECYCLE = -1
# 追踪对象的修改并且发送信号
SQLALCHEMY_TRACK_MODIFICATIONS = False
源码分析
我们就来简单的看下源码流程
首先从db = SQLAlchemy()
入手吧
def __init__(self, app=None, use_native_unicode=True, session_options=None,
metadata=None, query_class=BaseQuery, model_class=Model):
self.use_native_unicode = use_native_unicode
self.Query = query_class
self.session = self.create_scoped_session(session_options)
self.Model = self.make_declarative_base(model_class, metadata)
self._engine_lock = Lock()
self.app = app
_include_sqlalchemy(self, query_class)
if app is not None:
self.init_app(app)
初始化类中有几个属性Query、session 、Model 、app 还有一个方法init_app(app)
首先看下Query属性:
class BaseQuery(orm.Query):
该类有get_or_404、first_or_404、paginate3个方法,是做了查询异常处理,和分页数据
看看它的父类orm.Query
,它是sqlalchemy\orm\Query
类,定义了一些操作数据库的系列方法
然后看下session
属性
self.session = self.create_scoped_session(session_options)
def create_scoped_session(self, options=None):
if options is None:
options = {}
scopefunc = options.pop('scopefunc', _app_ctx_stack.__ident_func__)
options.setdefault('query_cls', self.Query)
return orm.scoped_session(
self.create_session(options), scopefunc=scopefunc
)
上述方法中scopefunc是从_app_ctx_stack = LocalStack()
中取如下方法
def _get__ident_func__(self):
return self._local.__ident_func__
options初始化字典,然后进行options.setdefault('query_cls', self.Query)
添加元素
然后通过self.create_session(options)
取构造sessionmaker
实例对象,然后在执行构造出来的实例对象的__call__
方法
在self.create_session(options)中,我们先看self.create_session部分,是返回一个sessionmaker
实例对象
return orm.sessionmaker(class_=SignallingSession, db=self, **options)
然后看下self.create_session(options)
,也就是sessionmaker
实例对象的__call__
方法
每次执行数据库操作时,都需要创建一个session,这个session就是sessionmaker的实例对象调用__call__
方法,以下是代码
def __call__(self, **local_kw):
"""Produce a new :class:`.Session` object using the configuration
established in this :class:`.sessionmaker`.
In Python, the ``__call__`` method is invoked on an object when
it is "called" in the same way as a function::
Session = sessionmaker()
session = Session() # invokes sessionmaker.__call__()
"""
for k, v in self.kw.items():
if k == 'info' and 'info' in local_kw:
d = v.copy()
d.update(local_kw['info'])
local_kw['info'] = d
else:
local_kw.setdefault(k, v)
return self.class_(**local_kw)
最后在create_scoped_session方法中返回如下:
return orm.scoped_session(
self.create_session(options), scopefunc=scopefunc
)
接下来我们看下self.Model
属性
self.Model = self.make_declarative_base(model_class, metadata)
def make_declarative_base(self, model, metadata=None):
"""Creates the declarative base that all models will inherit from.
:param model: base model class (or a tuple of base classes) to pass
to :func:`~sqlalchemy.ext.declarative.declarative_base`. Or a class
returned from ``declarative_base``, in which case a new base class
is not created.
:param: metadata: :class:`~sqlalchemy.MetaData` instance to use, or
none to use SQLAlchemy's default.
.. versionchanged 2.3.0::
``model`` can be an existing declarative base in order to support
complex customization such as changing the metaclass.
"""
if not isinstance(model, DeclarativeMeta):
model = declarative_base(
cls=model,
name='Model',
metadata=metadata,
metaclass=DefaultMeta
)
# if user passed in a declarative base and a metaclass for some reason,
# make sure the base uses the metaclass
if metadata is not None and model.metadata is not metadata:
model.metadata = metadata
if not getattr(model, 'query_class', None):
model.query_class = self.Query
model.query = _QueryProperty(self)
return model
我们在代码中会使用如下,是对象属性跟数据库字段的映射
class User(db.Model):
username = db.Column(db.String(80), unique=True)
pw_hash = db.Column(db.String(80))
然后看下SQLAlchemy初始化方法中的如下代码
_include_sqlalchemy(self, query_class)
def _include_sqlalchemy(obj, cls):
for module in sqlalchemy, sqlalchemy.orm:
for key in module.__all__:
if not hasattr(obj, key):
setattr(obj, key, getattr(module, key))
# Note: obj.Table does not attempt to be a SQLAlchemy Table class.
obj.Table = _make_table(obj)
obj.relationship = _wrap_with_default_query_class(obj.relationship, cls)
obj.relation = _wrap_with_default_query_class(obj.relation, cls)
obj.dynamic_loader = _wrap_with_default_query_class(obj.dynamic_loader, cls)
obj.event = event
意思就是获取relationship、event、dynamic_loader等进行关联查询、事件等操作的
最后看SQLAlchemy
类中的__init__
方法
if app is not None:
self.init_app(app)
就是为flask_app进行一些配置信息设置,
def init_app(self, app):
"""This callback can be used to initialize an application for the
use with this database setup. Never use a database in the context
of an application not initialized that way or connections will
leak.
"""
if (
'SQLALCHEMY_DATABASE_URI' not in app.config and
'SQLALCHEMY_BINDS' not in app.config
):
warnings.warn(
'Neither SQLALCHEMY_DATABASE_URI nor SQLALCHEMY_BINDS is set. '
'Defaulting SQLALCHEMY_DATABASE_URI to "sqlite:///:memory:".'
)
app.config.setdefault('SQLALCHEMY_DATABASE_URI', 'sqlite:///:memory:')
app.config.setdefault('SQLALCHEMY_BINDS', None)
app.config.setdefault('SQLALCHEMY_NATIVE_UNICODE', None)
app.config.setdefault('SQLALCHEMY_ECHO', False)
app.config.setdefault('SQLALCHEMY_RECORD_QUERIES', None)
app.config.setdefault('SQLALCHEMY_POOL_SIZE', None)
app.config.setdefault('SQLALCHEMY_POOL_TIMEOUT', None)
app.config.setdefault('SQLALCHEMY_POOL_RECYCLE', None)
app.config.setdefault('SQLALCHEMY_MAX_OVERFLOW', None)
app.config.setdefault('SQLALCHEMY_COMMIT_ON_TEARDOWN', False)
track_modifications = app.config.setdefault(
'SQLALCHEMY_TRACK_MODIFICATIONS', None
)
if track_modifications is None:
warnings.warn(FSADeprecationWarning(
'SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and '
'will be disabled by default in the future. Set it to True '
'or False to suppress this warning.'
))
app.extensions['sqlalchemy'] = _SQLAlchemyState(self)
@app.teardown_appcontext
def shutdown_session(response_or_exc):
if app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN']:
if response_or_exc is None:
self.session.commit()
self.session.remove()
return response_or_exc
我们在使用flask-sqlalchemy时,需要在项目为其进行设置,比如如下
class BaseConfig(object):
# SESSION_TYPE = 'redis' # session类型为redis
# SESSION_KEY_PREFIX = 'session:' # 保存到session中的值的前缀
# SESSION_PERMANENT = True # 如果设置为False,则关闭浏览器session就失效。
# SESSION_USE_SIGNER = False # 是否对发送到浏览器上 session:cookie值进行加密
SQLALCHEMY_DATABASE_URI = "mysql+pymysql://root:[email protected]:3306/test?charset=utf8"
SQLALCHEMY_POOL_SIZE = 5
SQLALCHEMY_POOL_TIMEOUT = 30
SQLALCHEMY_POOL_RECYCLE = -1
# 追踪对象的修改并且发送信号
SQLALCHEMY_TRACK_MODIFICATIONS = False
以上就是db = SQLAlchemy()进行的初始化操作,然后我们通过如下的代码生成数据库表
app = create_app()
#从栈拿app
with app.app_context():
# db.drop_all()
db.create_all()
# data = db.session.query(models.Users).all()
# print(data)
我们在初始化就提到过scopefunc = options.pop('scopefunc', _app_ctx_stack.__ident_func__)
所以我们需要通过with app.app_context():
获取atx,以下是with函数需要调用的方法
def __enter__(self):
self.push()
return self
def __exit__(self, exc_type, exc_value, tb):
self.pop(exc_value)
if BROKEN_PYPY_CTXMGR_EXIT and exc_type is not None:
reraise(exc_type, exc_value, tb)
然后进行创建数据库表
def create_all(self, bind='__all__', app=None):
self._execute_for_all_tables(app, bind, 'create_all')
def _execute_for_all_tables(self, app, bind, operation, skip_tables=False):
app = self.get_app(app)
if bind == '__all__':
binds = [None] + list(app.config.get('SQLALCHEMY_BINDS') or ())
elif isinstance(bind, string_types) or bind is None:
binds = [bind]
else:
binds = bind
for bind in binds:
extra = {}
if not skip_tables:
tables = self.get_tables_for_bind(bind)
extra['tables'] = tables
op = getattr(self.Model.metadata, operation)
op(bind=self.get_engine(app, bind), **extra)
以上就是flask-sqlalchemy的大概执行流程