Building Database Applications in Elixir with Ecto/

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Cast and Filter

Cast and Filter

Learn how to cast and filter data.

We'll cover the following...

The following example inserts a new Artist record based on data supplied by the user:

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import Ecto.Changeset
params = %{name: "Gene Harris"} 
changeset =
  %Artist{} \
  |> cast(params, [:name]) \
  |> validate_required([:name])
case Repo.insert(changeset) do
  {:ok, artist} -> IO.puts("Record for #{artist.name} was created.") 
  {:error, changeset} -> IO.inspect(changeset.errors)
end

As this example demonstrates, changesets help us with the entire life cycle of making a change, starting with raw data and ending with the operation succeeding or failing at the database level. Let’s now zoom in on each step.

The first step is to take the raw input data that we want to apply to the database and generate an Ecto.Changeset struct. We call this “casting and filtering” because we perform any needed type casting operations, like turning a string into an integer, and filter out any values we don’t want to use. We can do this two different ways, depending on where our data is coming from. We’ll look at both in the following sections.

Create changesets using internal data

If the data is internal to the application, we can create a changeset using the Ecto.Changeset.change function. Here’s how we would create a changeset that inserts a new Artist record:

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import Ecto.Changeset
changeset = change(%Artist{name: "Charlie Parker"})

The import statement makes all of the functions in Ecto.Changeset available to our code. We won’t include this in the rest of the examples for brevity.

The process of making changes to an existing record is similar, but instead of passing in a new struct, ...