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I'm using the SQLAlchemy Python ORM in a Pylons project. I have a class "Project" which has a one to many relationship with another class "Entry". I want to do a query in SQLAlchemy that gives me all of the projects which have one or more entries associated with them. At the moment I'm doing:
[project for project in Session.query(Project) if len(project.entries)>0]
which I know isn't ideal, but I can't figure out how to do a filter that does what I require (e.g. Session.query(Project).filter(Project.entries.exists())).
Any ideas?
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The second one, filter_by(), may be used only for filtering by something specifically stated - a string or some number value. So it's usable only for category filtering, not for expression filtering. On the other hand filter() allows using comparison expressions (==, <, >, etc.)
method sqlalchemy.orm.Query. all() Return the results represented by this Query as a list. This results in an execution of the underlying SQL statement. The Query object, when asked to return either a sequence or iterator that consists of full ORM-mapped entities, will deduplicate entries based on primary key.
The alias in SQL corresponds to a “renamed” version of a table or SELECT statement, which occurs anytime you say “SELECT * FROM table1 AS a”. The AS creates a new name for the table. Aliases allow any table or subquery to be referenced by a unique name.
All SELECT statements generated by SQLAlchemy ORM are constructed by Query object. It provides a generative interface, hence successive calls return a new Query object, a copy of the former with additional criteria and options associated with it.
Session.query(Project).filter(Project.entries.any()) should work.
Edited credit of James Brady's comment, be sure to give him some love.
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