Python SQLAlchemy Query using labeled OVER clause with ORM
This other question says how to use the OVER clause on sqlalchemy:
Using the OVER window function in SQLAlchemy
But how to do that using ORM? I have something like:
q = self.session.query(self.entity, func.count().over().label('count_over'))
This fails when I call
q.all() with the following message:
sqlalchemy.exc.InvalidRequestError: Ambiguous column name 'count(*) OVER ()' in result set! try 'use_labels' option on select statement
How can I solve this?
You have the
over syntax almost correct, it should be something like this:
import sqlalchemy q = self.session.query( self.entity, sqlalchemy.over(func.count()).label('count_over'), )
Example from the docs:
from sqlalchemy import over over(func.row_number(), order_by='x')
Query API, This section presents the API reference for the ORM Query object. This results in an execution of the underlying SQL statement. 'evaluate' - Evaluate the query's criteria in Python straight on the objects in the session. by this Query , converted to a scalar subquery with a label of the given name. The following are code examples for showing how to use sqlalchemy.orm.session.query().They are from open source Python projects. You can vote up the examples you like or vote down the ones you don't like.
SQLAlchemy Query object has
with_entities method that can be used to customize the list of columns the query returns:
Resulting in following SQL:
SELECT models.foo AS models_foo, count(*) OVER () AS count_over FROM models
Column Elements and Expressions, The and_() conjunction is also available using the Python & operator (though and the string SQL statement will be transformed on a per-execution Using IN expressions - with baked queries A label changes the name of an element in the columns clause of a Using Textual SQL - in the ORM tutorial. method sqlalchemy.orm.query.Query. label (name) ¶ Return the full SELECT statement represented by this Query, converted to a scalar subquery with a label of the given name. Analogous to SelectBase.label(). attribute sqlalchemy.orm.query.Query. lazy_loaded_from = None¶ An InstanceState that is using this Query for a lazy load operation.
You got the functions right. They way to use them to produce the desired result would be as follows:
from sqlalchemy import func q = self.session.query(self.entity, func.count(self.entity).over().label('count_over'))
This will produce a
COUNT(*) statement since no
Entity.field was specified. I use the following format:
from myschema import MyEntity from sqlalchemy import func q = self.session.query(MyEntity, func.count(MyEntity.id).over().label('count'))
That is if there is an id field, of course. But you get the mechanics :-)
SQL Expression Language Tutorial, Whereas the ORM, introduced in Object Relational Tutorial, presents a high In this case the SQLite dialect will interpret instructions to the Python built-in sqlite3 module. a BETWEEN clause, and ColumnElement.label() is used in a column Using Textual SQL - integrating ORM-level queries with text() The following are code examples for showing how to use sqlalchemy.orm.Query().They are from open source Python projects. You can vote up the examples you like or vote down the ones you don't like.
Object Relational Tutorial, When using the ORM, we typically don't use the Engine directly once the Column objects with special Python accessors known as descriptors; So if running this tutorial on one of those databases, and you wish to use SQLAlchemy sql>>> for row in session.query(User.name.label('name_label')).all(): SQLAlchemy's ORM query API simplifies the way we write database queries. Instead of writing raw SQL queries, we can construct queries on our SQLAlchemy session by chaining together methods to retrieve data. We're going to dive into SQLAlchemy's extensive query API to get an idea of all the ways we can query our data.
SQL Expressions as Mapped Attributes, Attributes on a mapped class can be linked to SQL expressions, which can be used in Often, the SQL expression must be distinguished from the Python expression, using the if statement in Python and the case() construct for SQL expressions: from sqlalchemy.orm import with_expression q = session.query(A).options( The following are code examples for showing how to use sqlalchemy.orm.attributes.InstrumentedAttribute().They are from open source Python projects. You can vote up the examples you like or vote down the ones you don't like.
Nested Queries with SQLAlchemy ORM, In SQL, the grouping is done with the following statement: If you were to run the above query on the example data I provided, the result would be: Flask-SQLAlchemy makes working with sessions much easier, so I In SQLAlchemy, the label() method applied to a column achieves the same result. construct used by the ORM to construct database queries. The :class:`.Query` class should not be confused with the. :class:`.Select` class, which defines database. SELECT operations at the SQL (non-ORM) level.