Don't migrate between text and varchar in Postgres / domains #762
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* These types are synonyms, with the exact same memory representation in Postgres * So there's no need to suggest migrating from one to the other https://stackoverflow.com/a/4849030/1176156
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Postgres supports the concept of domains, which are data types with optional constraints. An app might make an "email" domain over the varchar type, with a CHECK that the emails are valid In this case the generated SQL should use the domain name: ALTER TABLE users ALTER COLUMN foo TYPE email Previously the migration code only looked at the underlying type (varchar), and tried to migrate something already of the domain email back to an email.
MaxGabriel
commented
Dec 19, 2017
| type SafeToRemove = Bool | ||
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| data AlterColumn = Type SqlType Text | ||
| data AlterColumn = ChangeType SqlType Text |
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In the course of debugging this issue I found it extremely hard to search for Type, so I renamed this to ChangeType.
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My use case is that I have a database not using Persistent for migrations, and I want to use persistent to interact with it. I would also like to check that Persistent's models match the database schema by running
getMigrationand ensuring there are no changes to be made, but if there are spurious migrations then I'll have false positives.In this database,
textis being used instead ofvarchar, so Persistent claims it needs migrations. Sincetextandvarcharare synonyms, this should be unnecessary.Edit:
I found another, similar issue where Persistent would try to migrate a domained type to itself. This needed all the same test infrastructure and has the same theme, so I added it here. This is documented extensively in the comments; see there for details.