How to update or insert with SQLite.swift

In this example, the user dictionary stores words that are typed on a custom keyboard. If the word is already in the dictionary, then that word's frequency count is incremented by 1. But if the word hasn't been entered before, then a new row is inserted with a default frequency of 1.

The table was created with the following schema:

let userDictionary = Table("user_dictionary")
let wordId = Expression<Int64>("id")
let word = Expression<String>("word")
let frequency = Expression<Int64>("frequency")        

// ...

let _ = try db.run( userDictionary.create(ifNotExists: true) {t in
    t.column(wordId, primaryKey: true)
    t.column(word, unique: true)
    t.column(frequency, defaultValue: 1)
    })

Taken from the question, this is what we want to do:

1. Begin a transaction
2. Do the update
3. Check the rowcount
4. If it is 0 do the insert
5. Commit

Here is how the code would look.

let wordToUpdate = "hello"

// ...

// 1. wrap everything in a transaction
try db.transaction {

    // scope the update statement (any row in the word column that equals "hello")
    let filteredTable = userDictionary.filter(word == wordToUpdate)

    // 2. try to update
    if try db.run(filteredTable.update(frequency += 1)) > 0 { // 3. check the rowcount

        print("updated word frequency")

    } else { // update returned 0 because there was no match

        // 4. insert the word
        let rowid = try db.run(userDictionary.insert(word <- wordToUpdate))
        print("inserted id: \(rowid)")
    }
} // 5. if successful, transaction is commited

See the SQLite.swift documentation for more help.