Flask---flask_sqlalchemy源码分析

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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:root@127.0.0.1:3306/test?charset=utf8"SQLALCHEMY_POOL_SIZE = 5SQLALCHEMY_POOL_TIMEOUT = 30SQLALCHEMY_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_unicodeself.Query = query_classself.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 configurationestablished in this :class:`.sessionmaker`.In Python, the ``__call__`` method is invoked on an object whenit 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'] = delse: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 passto :func:`~sqlalchemy.ext.declarative.declarative_base`. Or a classreturned from ``declarative_base``, in which case a new base classis not created.:param: metadata: :class:`~sqlalchemy.MetaData` instance to use, ornone to use SQLAlchemy's default... versionchanged 2.3.0::``model`` can be an existing declarative base in order to supportcomplex 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 metaclassif metadata is not None and model.metadata is not metadata:model.metadata = metadataif not getattr(model, 'query_class', None):model.query_class = self.Querymodel.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 theuse with this database setup.  Never use a database in the contextof an application not initialized that way or connections willleak."""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_appcontextdef 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:root@127.0.0.1:3306/test?charset=utf8"SQLALCHEMY_POOL_SIZE = 5SQLALCHEMY_POOL_TIMEOUT = 30SQLALCHEMY_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 selfdef __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 = bindfor bind in binds:extra = {}if not skip_tables:tables = self.get_tables_for_bind(bind)extra['tables'] = tablesop = 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

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