CODEWITHSUNDEEP
pythonsqlalchemy
blue note
blue note

Reputation: 29081

sqlalchemy: rename a column on *query* level

I need to rename a column in a query, but I can't do it on column level, eg

session.query(MyModel.col_name.label('new_name'))

Is there any way to rename a column on the resulting query object?

Eg, something like

session.query(...).blah().blah().rename_column('old_name', 'new_name')

Upvotes: 6

Views: 4942

Answers (2)

B T
B T

Reputation: 60875

I've figured out a way to do this. In my case, I was having issues with except_, which prefixes columns with the table name. Here's how I did that:

def _except(included_query, excluded_query, Model, prefix):
    """An SQLALchemy except_ that removes the prefixes on the columns, so they can be
    referenced in a subquery by their un-prefixed names."""
    query = included_query.except_(excluded_query)
    subquery = query.subquery()
    # Get a list of columns from the subquery, relabeled with the simple column name.
    columns = []
    for column_name in _attribute_names(Model):
        column = getattr(subquery.c, prefix + column_name)
        columns.append(column.label(column_name))
    # Wrap the query to select the simple column names. This is necessary because
    # except_ prefixes column names with a string derived from the table name.
    return Model.query.from_statement(Model.query.with_entities(*columns).statement)

Upvotes: 0

Yaakov Bressler
Yaakov Bressler

Reputation: 12018

It doesn't look like there's any built in solution for that – but here's a workaround I've implemented which may help you:

To rename before the query has been executed:

# Start off with your regular query – but as a subquery
query = session.query(MyModel.col_name.label('old_name')).subquery()

# Now, perform a second query with new labels
query_2 = session.query(query.c.old_name.label('new_name'))

# Or, if there's only one column:
query_3 = session.query(query.label('new_name'))

Upvotes: 2

Related Questions