feat: enables users to add custom query filters

[subaru9]

Overview

Added the EctoShorts.QueryBuilder.Custom behavior. This module enables the addition of custom query filters to the query builder through a custom module defined in the configuration of the dependent application.

Example

An example of how custom filters can be implemented using the EctoShorts.QueryBuilder.Custom behavior.

This module offers the following features:

• Defines custom filters such as :select_balance_field_only, :currency_code, and :amount_gte.
• Implements the create_custom_schema_filter/2 function to build queries based on custom filter types.

  
defmodule MyApp.EctoShorts.QueryBuilder.Custom do
  import Ecto.Query, only: [select: 3, where: 3]

  alias EctoShorts.QueryBuilder.Custom

  @behaviour Custom

  @custom_filters [:select_balance_field_only, :currency_code, :amount_gte]

  @impl Custom
  def custom_filters, do: @custom_filters

  @impl Custom
  def create_custom_schema_filter({:select_balance_field_only, true}, query),
    do: select(query, [b], b.balance)
  def create_custom_schema_filter({:select_balance_field_only, _}, query), do: query

  @impl Custom
  def create_custom_schema_filter({:currency_code, val}, query) do
    where(query, [b], fragment("(?).currency_code = ?", b.balance, ^to_string(val)))
  end

  @impl Custom
  def create_custom_schema_filter({:amount_gte, val}, query) do
    where(query, [b], fragment("(?).amount >= ?", b.balance, ^val))
  end
end