Defines how DataSchema.to_struct/2 should access data for each given field type.

When we create a struct defined by the schema we will visit each struct field in turn and attempt to extract values from the source data. You tell the schema how to extract that data by providing a module that implements this behaviour. Modules that implement this behaviour are implementing how to access data in the source for each kind of field.

Examples

To define a schema that consumes a map to create a struct you would first create a module that implements this behaviour like so:

defmodule DataSchema.MapAccessor do
  @behaviour DataSchema.DataAccessBehaviour

  @impl true
  def field(data = %{}, field) do
    Map.get(data, field)
  end

  @impl true
  def list_of(data = %{}, field) do
    Map.get(data, field)
  end

  @impl true
  def has_one(data = %{}, field) do
    Map.get(data, field)
  end

  @impl true
  def has_many(data = %{}, field) do
    Map.get(data, field)
  end
end

Then you would pass it into the schema definition:

defmodule BlogPost do
  import DataSchema, only: [data_schema: 2]

  data_schema([
    field: {:content, "content", &{:ok, to_string(&1)}}
  ], DataSchema.MapAccessor)
end

When we call DataSchema.to_struct/2 the functions in DataSchema.MapAccessor will be used to access the data from the source.

DataSchema ships with the above example (see DataSchema.MapAccessor) and you can use DataSchema.data_schema/1 to leverage it automatically.