Does Ecto.Changeset.cast provide a global configuration for empty_strings_to_nil?

Answer

There is no global configuration in Ecto that automatically sets empty_strings_to_nil: true for every Ecto.Changeset.cast/4 call. The option must be supplied explicitly on each cast, or you must provide your own helper that injects it.

Why the Option Is Per‑Call

The cast/4 implementation only accepts an opts keyword list. Internally it looks for the :empty_strings_to_nil flag and applies it to the fields it processes. There is no place in the Ecto source that reads a global configuration value, so the behavior cannot be changed without touching the library itself.

Recommended Project‑Wide Strategies

1. Wrap cast/4 in a helper function

   defmodule MyApp.Casts do
     def cast(changeset, schema, params, required, optional) do
       Ecto.Changeset.cast(changeset, schema, params, required, optional, empty_strings_to_nil: true)
     end
   end
   
   # Usage
   changeset = MyApp.Casts.cast(%MyApp.User{}, params, [:name], [:age])

2. Define a macro that injects the option

   defmacro cast_with_nil(changeset, schema, params, required, optional) do
     quote do
       Ecto.Changeset.cast(unquote(changeset), unquote(schema), unquote(params),
         unquote(required), unquote(optional), empty_strings_to_nil: true)
     end
   end

3. Use Phoenix LiveView’s form handling

   When you use form_for or live_form in a LiveView, Phoenix automatically sets empty_strings_to_nil: true on the underlying changeset. This covers the majority of web‑form use cases, but it does not affect API endpoints or other contexts.

When to Choose Which Approach

• API‑only projects: A wrapper module is the simplest way to enforce the policy across all changesets.
• Mixed web/API projects: Combine the LiveView automatic conversion with a wrapper for non‑LiveView code.
• Large codebases with many schemas: A macro can reduce boilerplate while keeping the syntax close to the original cast/4 call.

Verification Steps

1. Create a changeset that casts an empty string field without the option and confirm it remains an empty string.
2. Apply the wrapper/macro and verify the field becomes nil.
3. Run a quick unit test against a real database to ensure NULL is persisted.

Missing Diagnostic Detail

Are you using Phoenix LiveView for form submissions, or are all casts occurring in plain Elixir modules? Knowing this will help decide whether the LiveView automatic conversion suffices or a custom wrapper is required.