Rails index uniqueness with specific value

Question

I'd like to create a unique index for a table, consisting of 3 columns, but to check only if one of them has a specific value:

something like add_index :table, [:col1, :col2, :col3], unique: true

but only if col3 = true, otherwise I don't care about col1, col2, :col3 = false uniqueness.

is there a way to do it in a migration to keep it at the DB level, or can I only validate this case in the model?

mattforni · Accepted Answer · 2014-11-19 17:22:58Z

2

I don't believe you can have conditional uniqueness constraints at the database layer (via migrations). You can add this as a conditional validation at the AR layer though which should be sufficient for your purposes (though it should be noted this can introduce some race conditions). ie.

validates [:col1, :col2], uniqueness: true, if: ":col3 == true"

Hope that helps.

answered Nov 19, 2014 at 17:22

mattforni

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