Sqlite.Function

Create and add custom functions to a SQLite database.

Sqlite.Function.register "add_one" db <| 
    Sqlite.Function.arg Decode.int <| \num ->
    Sqlite.Function.return (Encode.int (num + 1))

Function arguments must be decoded with Sqlite.Decode and the return value of the function must be an encoded with Sqlite.Encode.

The above function can then be using in SQL.

SELECT answer FROM answers WHERE answer_number = add_one(1)

For this example, answer_number in the SQL above you be equivalant to writing answer_number = 2 and will be evaluated by SQLite as such.

Functions can have any number of arguments by stringing together multiple arg functions for each expected argument. All arguments are expected to be provided when using the function in SQL.

Due to limitations in the underlying Node SQLite implementation, custom functions do not error. Instead, any failures change the return value of the function to null.

type Function

A custom SQLite function. This function can be used in a database by giving it as an argument to the register function.
arg : Decoder a -> (a -> Function) -> Function

An argument in a custom SQLite function. The argument must be decoded into a Gren value by using a Sqlite.Decode.Decoder.
return : Value -> Function

The encoded SQLite value that's returned by a custom SQLite function. This return value is what will be handed to SQLite and must be encoded as Sqlite.Encode.Value.
register : String -> Database -> Function -> Task a {}

Register a given Function with the given SQLite Database, allowing it to be used in SQL queries.

Functions must be registered with a database each time it's opened and used. It's recommended you register all necessary functions right after opening the database.