这部分文档叙述了所有 Flask-SQLAlchemy 中的公共类和函数。


class flask.ext.sqlalchemy.SQLAlchemy(app=None, use_native_unicode=True, session_extensions=None, session_options=None)

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 similar. 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.request_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.


BaseQuery 类。

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 SQLALCHEMY_NATIVE_UNICODE.

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.

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 leak.

make_connector(app, bind=None)

Creates the connector for a given state and bind.


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.


可选地声明要使用的 bind 。 None 为默认的 bind 。更多信息见 :ref:`binds 。

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.




对查询应用一个或更多 ORDER BY 约束,并返回新的结果查询。


对应用一个 LIMIT ,并返回新的结果查询。


对查询应用一个 OFFSET ,并返回新的结果查询。


返回此查询中的第一个结果,如果结果不包含任何行,返回 None 。 这会执行底层查询。


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 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, per_page=20, 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.

Returns an Pagination object.


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 != pagination.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 attributes:

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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