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POHow to alter column type from character varying to integer using sqlalchemy-migrate
 

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  1. POHow to alter column type from character varying to integer using sqlalchemy-migrate
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    <p>I'm using sqlalchemy-migrate to alter the type of one of the columns in a table in a Postgre SQL database. The upgrade script I'm using is:</p> <pre class="lang-python prettyprint-override"><code># -*- cofing: utf-8 -*- from sqlalchemy import MetaData, Table, Column, String, Integer from migrate import changeset metadata = MetaData() def upgrade(migrate_engine): # ALTER TABLE courses ALTER COLUMN number SET DATA TYPE character varying; metadata.bind = migrate_engine courses = Table('courses', metadata, Column("number", Integer), extend_existing=True) courses.c.number.alter(type=String) def downgrade(migrate_engine): # ALTER TABLE courses ALTER COLUMN number SET DATA TYPE integer; metadata.bind = migrate_engine courses = Table('courses', metadata, Column("number", String), extend_existing=True) courses.c.number.alter(type=Integer, cast='numeric') </code></pre> <p>The upgrade part seems to work but the downgrade always fails with the following error:</p> <pre><code>sqlalchemy.exc.ProgrammingError: (ProgrammingError) column "number" cannot be cast to type integer '\nALTER TABLE courses ALTER COLUMN number TYPE INTEGER' {} </code></pre> <p>Now, if I were using plain SQL I could use <code>ALTER TABLE courses ALTER COLUMN number TYPE INTEGER USING number::numeric</code> to alter the column type back from <code>character varying</code> to <code>integer</code>, but I don't know how to achieve that using sqlalchemy-migrate.</p> <p>Is there a way to force sqlalchemy to include <code>USING number::numeric</code> in the <code>ALTER</code> clause? or is there another way to avoid the error I posted above?</p> <p>I appreciate your help.</p>
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    1. USWillington Vega
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