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(* Module for a specific record type *)
module User = struct
  type t = { id : int; name : string }

  (* Database-specific functions for User records *)
  module Queries = struct
    let get_user_by_id (id : int) : t option =
      (* Database query implementation *)
      ...

    let insert_user (user : t) : unit =
      (* Database query implementation *)
      ...
  end
end

In this approach, the User module defines the record type t representing a user. Within the User module, we have an inner module Queries that encapsulates the database-specific functions for interacting with User records. Here, we have two functions: get_user_by_id retrieves a user from the database based on the provided ID, and insert_user inserts a user record into the database.

Alternatively, you can use a separate module responsible for database operations that can be parameterized by the record type module using functors. Here's an example:

(* Module for database operations *)
module DatabaseOperations (R : sig
  type t
  (* Additional record type specific requirements, if any *)
end) = struct
  let get_by_id (id : int) : R.t option =
    (* Database query implementation *)
    ...

  let insert (record : R.t) : unit =
    (* Database query implementation *)
    ...
end

(* Module for a specific record type *)
module User = struct
  type t = { id : int; name : string }
end

(* Module that includes database operations for User records *)
module UserDatabaseOperations = DatabaseOperations(User)

In this approach, we define a separate module DatabaseOperations that is parameterized by a record type module R. The DatabaseOperations module contains generic database operations such as get_by_id and insert that can work with any record type. We then instantiate the DatabaseOperations module for the specific User record type, resulting in the UserDatabaseOperations module that includes the database operations specifically tailored for User records.

By using functors, we can achieve code reusability and encapsulation of database operations while maintaining type safety and modularity.

These examples showcase two different approaches to organizing database-related code in OCaml. The choice between them depends on the specific requirements and structure of your application.