Optimizing Validations with Caching

When we have a Member model where each user has a specific number of coins. When performing operations like capturing or deducting coins, we want to validate:

1. The user exists or not.
2. The user has enough coins to complete the operation.
The basic validation will look like this (with dry-validation gem)

class CoinsValidator < Dry::Validation::Contract
  params do
    required(:user).filled(:integer)
    required(:coins).filled(:integer, gt?: 0)
  end

  rule(:user) do
    member = Member.find_by(unique_id: value) // querying database for member details
    key.failure("does not exist") if member.nil?
  end

  rule(:coins, :user) do
    member = Member.find_by(unique_id: values[:user]) // querying database for member details
    if member && member.coins < values[:coins]
      key(:coins).failure("are insufficient")
    end
  end
end

But the problem here is, We query the database twice to fetch the same Member object once in the :user rule and again in the :coins rule. This redundant querying increases database load and slows down validation, especially in high-traffic applications.

To avoid redundant queries, we can cache the Member object using the values hash provided by the dry-validation gem. The values hash allows us to store intermediate results, making them accessible to other validation rules.
The optimized code looks like this:

class CoinsValidator < Dry::Validation::Contract
  params do
    required(:user).filled(:integer)
    required(:coins).filled(:integer, gt?: 0)
  end

  rule(:user) do
    values[:member] = Member.find_by(unique_id: value)  // Caching the member object
    key.failure("does not exist") if values[:member].nil?
  end

  rule(:coins) do
    member = values[:member]  // accessing the cached Member from values[:member] rather than querying the database again.
    if member && member.coins < value
      key.failure("are insufficient")
    end
  end
end

#ruby on rails