How to create an SQL View with SQLAlchemy?

Update: See also the SQLAlchemy usage recipe here

Creating a (read-only non-materialized) view is not supported out of the box as far as I know. But adding this functionality in SQLAlchemy 0.7 is straightforward (similar to the example I gave here). You just have to write a compiler extension CreateView. With this extension, you can then write (assuming that t is a table object with a column id)

createview = CreateView('viewname', t.select().where(t.c.id>5))engine.execute(createview)v = Table('viewname', metadata, autoload=True)for r in engine.execute(v.select()):    print r

Here is a working example:

from sqlalchemy import Tablefrom sqlalchemy.ext.compiler import compilesfrom sqlalchemy.sql.expression import Executable, ClauseElementclass CreateView(Executable, ClauseElement):    def __init__(self, name, select):        self.name = name        self.select = select@compiles(CreateView)def visit_create_view(element, compiler, **kw):    return "CREATE VIEW %s AS %s" % (         element.name,         compiler.process(element.select, literal_binds=True)         )# test datafrom sqlalchemy import MetaData, Column, Integerfrom sqlalchemy.engine import create_engineengine = create_engine('sqlite://')metadata = MetaData(engine)t = Table('t',          metadata,          Column('id', Integer, primary_key=True),          Column('number', Integer))t.create()engine.execute(t.insert().values(id=1, number=3))engine.execute(t.insert().values(id=9, number=-3))# create viewcreateview = CreateView('viewname', t.select().where(t.c.id>5))engine.execute(createview)# reflect view and print resultv = Table('viewname', metadata, autoload=True)for r in engine.execute(v.select()):    print r

If you want, you can also specialize for a dialect, e.g.

@compiles(CreateView, 'sqlite')def visit_create_view(element, compiler, **kw):    return "CREATE VIEW IF NOT EXISTS %s AS %s" % (         element.name,         compiler.process(element.select, literal_binds=True)         )

stephan's answer is a good one and covers most bases, but what left me unsatisfied was the lack of integration with the rest of SQLAlchemy (the ORM, automatic dropping etc.). After hours of experimenting and piecing together knowledge from all corners of the internet I came up with the following:

import sqlalchemy_viewsfrom sqlalchemy import Tablefrom sqlalchemy.ext.compiler import compilesfrom sqlalchemy.sql.ddl import DropTableclass View(Table):    is_view = Trueclass CreateView(sqlalchemy_views.CreateView):    def __init__(self, view):        super().__init__(view.__view__, view.__definition__)@compiles(DropTable, "postgresql")def _compile_drop_table(element, compiler, **kwargs):    if hasattr(element.element, 'is_view') and element.element.is_view:        return compiler.visit_drop_view(element)    # cascade seems necessary in case SQLA tries to drop     # the table a view depends on, before dropping the view    return compiler.visit_drop_table(element) + ' CASCADE'

Note that I am utilizing the sqlalchemy_views package, just to simplify things.

Defining a view (e.g. globally like your Table models):

from sqlalchemy import MetaData, text, Text, Columnclass SampleView:    __view__ = View(        'sample_view', MetaData(),        Column('bar', Text, primary_key=True),    )    __definition__ = text('''select 'foo' as bar''')# keeping track of your defined views makes things easierviews = [SampleView]

Mapping the views (enable ORM functionality):

Do when loading up your app, before any queries and after setting up the DB.

for view in views:    if not hasattr(view, '_sa_class_manager'):        orm.mapper(view, view.__view__)

Creating the views:

Do when initializing the database, e.g. after a create_all() call.

from sqlalchemy import ormfor view in views:    db.engine.execute(CreateView(view))

How to query a view:

results = db.session.query(SomeModel, SampleView).join(    SampleView,    SomeModel.id == SampleView.some_model_id).all()

This would return exactly what you expect (a list of objects that each has a SomeModel object and a SampleView object).

Dropping a view:

SampleView.__view__.drop(db.engine)

It will also automatically get dropped during a drop_all() call.

This is obviously a very hacky solution but in my eyes it is the best one and cleanest one out there at the moment. I have tested it these past few days and have not had any issues. I'm not sure how to add in relationships (ran into problems there) but it's not really necessary, as demonstrated above in the query.

If anyone has any input, finds any unexpected issues, or knows a better way to do things, please do leave a comment or let me know.

This was tested on SQLAlchemy 1.2.6 and Python 3.6.

These days there's a PyPI package for that: SQLAlchemy Views.

From it's PyPI Page:

>>> from sqlalchemy import Table, MetaData>>> from sqlalchemy.sql import text>>> from sqlalchemy_views import CreateView, DropView>>> view = Table('my_view', metadata)>>> definition = text("SELECT * FROM my_table")>>> create_view = CreateView(view, definition, or_replace=True)>>> print(str(create_view.compile()).strip())CREATE OR REPLACE VIEW my_view AS SELECT * FROM my_table

However, you asked for a no "pure SQL" query, so you probably want the definition above to be created with SQLAlchemy query object.

Luckily, the text() in the example above makes it clear that the definition parameter to CreateView is such a query object. So something like this should work:

>>> from sqlalchemy import Table, Column, Integer, String, MetaData, ForeignKey>>> from sqlalchemy.sql import select>>> from sqlalchemy_views import CreateView, DropView>>> 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=False)...  )

Here is the interesting bit:

>>> view = Table('my_view', metadata)>>> definition = select([users, addresses]).where(...     users.c.id == addresses.c.user_id... )>>> create_view = CreateView(view, definition, or_replace=True)>>> print(str(create_view.compile()).strip())CREATE OR REPLACE VIEW my_view AS SELECT users.id, users.name,users.fullname, addresses.id, addresses.user_id, addresses.email_address FROM users, addresses WHERE users.id = addresses.user_id