Support for multi-column primary keys? about grdb.swift HOT 4 CLOSED

Hello @schveiguy

It's not documented in the README, but you can pass a dictionary to the key argument of fetchOne:

MyRecord.fetchOne(db, key: ["col1": val1, "col2": val2])

Documentation is missing, but the feature is there to stay: I want GRDB to support any primary key.

This variant of fetchOne actually supports any key, not only primary keys, because it does not introspect the database schema. It implicitly requires that the dictionary columns are actually a table key, and returns the first record that matches.

Why did I not add any generic function that eats a tuple of 2, 3, ... N items? Because these functions would depend on the ordering of columns in the primary key. And this ordering is not always obvious, or may even be fragile (in case of wild schema change):

// Not supported, on purpose:
MyRecord.fetchOne(db, key: (1, 2))  // what is 1? what is 2?

So now, I suggest you write your own extension, as below :-)

extension MyRecord {
    static func fetchOne(db: Database, key: (Int64, Int)) -> MyRecord? {
        return fetchOne(db, ["col1": key.0, "col2": key.1])
    }
}

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Hm... yes, that's much better than my SQL string forward that I had written, thanks :)

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You're welcome 😄

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I added a paragraph in README.md: https://github.com/groue/GRDB.swift#fetching-by-primary-key

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