Documentation

Validates that e.g. an email (or another field) is unique across all users before inserting.

This validator reads the given field name (e.g. email) from the record, and runs a database query to check that there is no other record using the same field value (e.g. email value).

Example: Validate that an email is unique

action CreateUserAction = do
    let user = newRecord @User
    user
        |> fill @'["email"]
        |> validateIsUnique #email
        >>= ifValid \case
            Left user -> render NewView { .. }
            Right user -> do
                createRecord user
                redirectTo UsersAction

Case insensitive version of validateIsUnique.

Uses a comparison like LOWER(field) = LOWER(value) internally, so it's best to have an index for LOWER(field) in your Schema.sql

>>> CREATE UNIQUE INDEX users_email_index ON users ((LOWER(email)));

Example: Validate that an email is unique, ignoring case

action CreateUserAction = do
    let user = newRecord @User
    user
        |> fill @'["email"]
        |> validateIsUniqueCaseInsensitive #email
        >>= ifValid \case
            Left user -> render NewView { .. }
            Right user -> do
                createRecord user
                redirectTo UsersAction

Overrides the error message of a given IO validator function.

Example: Validate that an email is unique with a custom error message

action CreateUserAction = do
    let user = newRecord @User
    user
        |> fill @'["email"]
        |> withCustomErrorMessageIO "Email Has Already Been Used" validateIsUnique #email
        >>= ifValid \case
            Left user -> render NewView { .. }
            Right user -> do
                createRecord user
                redirectTo UsersAction