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FlaskSQLAlchemy教程 AI君 231℃

这部分文档记录了 Flask-SQLAlchemy 里的所有公开的类和函数。


class flask.ext.sqlalchemy.SQLAlchemy(app=None, use_native_unicode=True, session_options=None, metadata=None, query_class=<class ‘flask_sqlalchemy.BaseQuery’>, model_class=<class ‘flask_sqlalchemy.Model’>)

This class is used to control the SQLAlchemy integration to one
or more Flask applications. Depending on how you initialize the
object it is usable right away or will attach as needed to a
Flask application.

There are two usage modes which work very similarly. One is binding
the instance to a very specific Flask application:

app = Flask(__name__)
db = SQLAlchemy(app)

The second possibility is to create the object once and configure the
application later to support it:

db = SQLAlchemy()

def create_app():
    app = Flask(__name__)
    return app

The difference between the two is that in the first case methods like
create_all() and drop_all() will work all the time but in
the second case a flask.Flask.app_context() has to exist.

By default Flask-SQLAlchemy will apply some backend-specific settings
to improve your experience with them. As of SQLAlchemy 0.6 SQLAlchemy
will probe the library for native unicode support. If it detects
unicode it will let the library handle that, otherwise do that itself.
Sometimes this detection can fail in which case you might want to set
use_native_unicode (or the SQLALCHEMY_NATIVE_UNICODE configuration
key) to False. Note that the configuration key overrides the
value you pass to the constructor.

This class also provides access to all the SQLAlchemy functions and classes
from the sqlalchemy and sqlalchemy.orm modules. So you can
declare models like this:

class User(db.Model):
    username = db.Column(db.String(80), unique=True)
    pw_hash = db.Column(db.String(80))

You can still use sqlalchemy and sqlalchemy.orm directly, but
note that Flask-SQLAlchemy customizations are available only through an
instance of this SQLAlchemy class. Query classes default to
BaseQuery for db.Query, db.Model.query_class, and the default
query_class for db.relationship and db.backref. If you use these
interfaces through sqlalchemy and sqlalchemy.orm directly,
the default query class will be that of sqlalchemy.

Check types carefully

Don’t perform type or isinstance checks against db.Table, which
emulates Table behavior but is not a class. db.Table exposes the
Table interface, but is a function which allows omission of metadata.

You may also define your own SessionExtension instances as well when
defining your SQLAlchemy class instance. You may pass your custom instances
to the session_extensions keyword. This can be either a single
SessionExtension instance, or a list of SessionExtension instances. In the
following use case we use the VersionedListener from the SQLAlchemy
versioning examples.:

from history_meta import VersionedMeta, VersionedListener

app = Flask(__name__)
db = SQLAlchemy(app, session_extensions=[VersionedListener()])

class User(db.Model):
    __metaclass__ = VersionedMeta
    username = db.Column(db.String(80), unique=True)
    pw_hash = db.Column(db.String(80))

The session_options parameter can be used to override session
options. If provided it’s a dict of parameters passed to the
session’s constructor.

New in version 0.10: The session_options parameter was added.

New in version 0.16: scopefunc is now accepted on session_options. It allows specifying
a custom function which will define the SQLAlchemy session’s scoping.

New in version 2.1: The metadata parameter was added. This allows for setting custom
naming conventions among other, non-trivial things.


The BaseQuery class.

apply_driver_hacks(app, info, options)

This method is called before engine creation and used to inject
driver specific hacks into the options. The options parameter is
a dictionary of keyword arguments that will then be used to call
the sqlalchemy.create_engine() function.

The default implementation provides some saner defaults for things
like pool sizes for MySQL and sqlite. Also it injects the setting of

create_all(bind=’__all__’, app=None)

Creates all tables.

Changed in version 0.12: Parameters were added


Helper factory method that creates a scoped session. It
internally calls create_session().


Creates the session. The default implementation returns a

New in version 2.0.

drop_all(bind=’__all__’, app=None)

Drops all tables.

Changed in version 0.12: Parameters were added


Gives access to the engine. If the database configuration is bound
to a specific application (initialized with an application) this will
always return a database connection. If however the current application
is used this might raise a RuntimeError if no application is
active at the moment.


Helper method that implements the logic to look up an application.


Returns a dictionary with a table->engine mapping.

This is suitable for use of sessionmaker(binds=db.get_binds(app)).

get_engine(app, bind=None)

Returns a specific engine.

New in version 0.12.


Returns a list of all tables relevant for a bind.


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

make_connector(app, bind=None)

Creates the connector for a given state and bind.

make_declarative_base(model, metadata=None)

Creates the declarative base.


Returns the metadata

reflect(bind=’__all__’, app=None)

Reflects tables from the database.

Changed in version 0.12: Parameters were added


class flask.ext.sqlalchemy.Model

Baseclass for custom user models.


Optionally declares the bind to use. None refers to the default
bind. For more information see 绑定多个数据库.


The name of the table in the database. This is required by SQLAlchemy;
however, Flask-SQLAlchemy will set it automatically if a model has a
primary key defined. If the __table__ or __tablename__ is set
explicitly, that will be used instead.

query = None

an instance of query_class. Can be used to query the
database for instances of this model.


the query class used. The query attribute is an instance
of this class. By default a BaseQuery is used.

alias of BaseQuery

class flask.ext.sqlalchemy.BaseQuery(entities, session=None)

The default query object used for models, and exposed as
Query. This can be subclassed and
replaced for individual models by setting the query_class
attribute. This is a subclass of a standard SQLAlchemy
Query class and has all the methods of a
standard query as well.


Return the results represented by this query as a list. This
results in an execution of the underlying query.


apply one or more ORDER BY criterion to the query and return the
newly resulting query.


Apply a LIMIT to the query and return the newly resulting query.


Apply an OFFSET to the query and return the newly resulting


Return the first result of this query or None if the result
doesn’t contain any rows. This results in an execution of the
underlying query.


Like first() but aborts with 404 if not found instead of
returning None.


Return an instance based on the given primary key identifier,
or None if not found.


my_user = session.query(User).get(5)

some_object = session.query(VersionedFoo).get((5, 10))

get() is special in that it provides direct
access to the identity map of the owning Session.
If the given primary key identifier is present
in the local identity map, the object is returned
directly from this collection and no SQL is emitted,
unless the object has been marked fully expired.
If not present,
a SELECT is performed in order to locate the object.

get() also will perform a check if
the object is present in the identity map and
marked as expired – a SELECT
is emitted to refresh the object as well as to
ensure that the row is still present.
If not, ObjectDeletedError is raised.

get() is only used to return a single
mapped instance, not multiple instances or
individual column constructs, and strictly
on a single primary key value. The originating
Query must be constructed in this way,
i.e. against a single mapped entity,
with no additional filtering criterion. Loading
options via options() may be applied
however, and will be used if the object is not
yet locally present.

A lazy-loading, many-to-one attribute configured
by relationship(), using a simple
foreign-key-to-primary-key criterion, will also use an
operation equivalent to get() in order to retrieve
the target value from the local identity map
before querying the database. See /orm/loading_relationships
for further details on relationship loading.

Parameters: ident – A scalar or tuple value representing
the primary key. For a composite primary key,
the order of identifiers corresponds in most cases
to that of the mapped Table object’s
primary key columns. For a mapper() that
was given the primary key argument during
construction, the order of identifiers corresponds
to the elements present in this collection.
Returns: The object instance, or None.

Like get() but aborts with 404 if not found instead of
returning None.

paginate(page=None, per_page=None, error_out=True)

Returns per_page items from page page. By default it will
abort with 404 if no items were found and the page was larger than
1. This behavor can be disabled by setting error_out to False.

If page or per_page are None, they will be retrieved from the
request query. If the values are not ints and error_out is
true, it will abort with 404. If there is no request or they
aren’t in the query, they default to page 1 and 20

Returns an Pagination object.


class flask.ext.sqlalchemy.SignallingSession(db, autocommit=False, autoflush=True, app=None, **options)

The signalling session is the default session that Flask-SQLAlchemy
uses. It extends the default session system with bind selection and
modification tracking.

If you want to use a different session you can override the
SQLAlchemy.create_session() function.

New in version 2.0.

New in version 2.1: The binds option was added, which allows a session to be joined
to an external transaction.

app = None

The application that this session belongs to.


class flask.ext.sqlalchemy.Pagination(query, page, per_page, total, items)

Internal helper class returned by BaseQuery.paginate(). You
can also construct it from any other SQLAlchemy query object if you are
working with other libraries. Additionally it is possible to pass None
as query object in which case the prev() and next() will
no longer work.


True if a next page exists.


True if a previous page exists

items = None

the items for the current page

iter_pages(left_edge=2, left_current=2, right_current=5, right_edge=2)

Iterates over the page numbers in the pagination. The four
parameters control the thresholds how many numbers should be produced
from the sides. Skipped page numbers are represented as None.
This is how you could render such a pagination in the templates:

{% macro render_pagination(pagination, endpoint) %}
  <div class=pagination>
  {%- for page in pagination.iter_pages() %}
    {% if page %}
      {% if page != %}
        <a href="{{ url_for(endpoint, page=page) }}">{{ page }}</a>
      {% else %}
        <strong>{{ page }}</strong>
      {% endif %}
    {% else %}
      <span class=ellipsis></span>
    {% endif %}
  {%- endfor %}
{% endmacro %}

Returns a Pagination object for the next page.


Number of the next page

page = None

the current page number (1 indexed)


The total number of pages

per_page = None

the number of items to be displayed on a page.


Returns a Pagination object for the previous page.


Number of the previous page.

query = None

the unlimited query object that was used to create this
pagination object.

total = None

the total number of items matching the query


In debug mode Flask-SQLAlchemy will log all the SQL queries sent
to the database. This information is available until the end of request
which makes it possible to easily ensure that the SQL generated is the
one expected on errors or in unittesting. If you don’t want to enable
the DEBUG mode for your unittests you can also enable the query
recording by setting the 'SQLALCHEMY_RECORD_QUERIES' config variable
to True. This is automatically enabled if Flask is in testing mode.

The value returned will be a list of named tuples with the following

The SQL statement issued
The parameters for the SQL statement
start_time / end_time
Time the query started / the results arrived. Please keep in mind
that the timer function used depends on your platform. These
values are only useful for sorting or comparing. They do not
necessarily represent an absolute timestamp.
Time the query took in seconds
A string giving a rough estimation of where in your application
query was issued. The exact format is undefined so don’t try
to reconstruct filename or function name.

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