unikernel/duniverse/pgx/pgx_async/bin/pgx_async_example.ml

@@ -0,0 +1,141 @@
+(* A basic example of Pgx_async usage *)
+open Core_kernel
+open Async_kernel
+open Async_unix
+
+module Employee = struct
+  let create db =
+    Pgx_async.simple_query
+      db
+      {|
+      CREATE TEMPORARY TABLE Employee (
+        id SERIAL PRIMARY KEY,
+        name VARCHAR(100) NOT NULL UNIQUE);
+    |}
+    |> Deferred.ignore_m
+  ;;
+
+  (* This function lets us insert multiple users relatively efficiently *)
+  let insert_many db names =
+    let params = List.map names ~f:(fun name -> Pgx_async.Value.[ of_string name ]) in
+    Pgx_async.execute_many
+      db
+      ~params
+      ~query:
+        {|
+      INSERT INTO Employee (name)
+      VALUES ($1)
+      RETURNING id
+    |}
+    >>| List.map ~f:(function
+            | [ [ id ] ] -> Pgx.Value.to_int_exn id
+            | _ -> assert false)
+  ;;
+
+  let insert ~name db = insert_many db [ name ] >>| List.hd_exn
+end
+
+module Facility = struct
+  let create db =
+    Pgx_async.simple_query
+      db
+      {|
+      CREATE TEMPORARY TABLE Facility (
+        id SERIAL PRIMARY KEY,
+        name VARCHAR(100) NOT NULL UNIQUE,
+        director_id INT REFERENCES Employee(id) ON DELETE SET NULL);
+
+      CREATE INDEX facility_director_id ON Facility (director_id);
+    |}
+    |> Deferred.ignore_m
+  ;;
+
+  let insert ~name ?director_id db =
+    let params = Pgx_async.Value.[ of_string name; opt of_int director_id ] in
+    Pgx_async.execute
+      db
+      ~params
+      {|
+      INSERT INTO Facility (name, director_id)
+      VALUES ($1, $2)
+      RETURNING id
+    |}
+    >>| function
+    | [ [ id ] ] -> Pgx.Value.to_int_exn id
+    | _ -> assert false
+  ;;
+
+  let all_name_and_director_name db =
+    Pgx_async.execute
+      db
+      {|
+      SELECT f.name, e.name
+      FROM Facility f
+      LEFT JOIN Employee e ON e.id = f.director_id
+    |}
+    >>| List.map ~f:(function
+            | [ name; director_name ] ->
+              Pgx.Value.(to_string_exn name, to_string director_name)
+            | _ -> assert false)
+  ;;
+
+  let reassign_director db ~director_id ~from_facility_id ~to_facility_id =
+    (* Note: with_transaction doesn't currently have any special handling
+       for concurrent queries *)
+    Pgx_async.with_transaction db
+    @@ fun db ->
+    let params = Pgx.Value.[ of_int director_id; of_int from_facility_id ] in
+    Pgx_async.execute
+      db
+      ~params
+      {|
+      UPDATE Facility SET director_id = NULL WHERE id = $2 AND director_id = $1
+    |}
+    >>= fun _ ->
+    let params = Pgx.Value.[ of_int director_id; of_int to_facility_id ] in
+    Pgx_async.execute
+      db
+      ~params
+      {|
+      UPDATE Facility SET director_id = $1 WHERE id = $2
+    |}
+    |> Deferred.ignore_m
+  ;;
+end
+
+let setup db = Employee.create db >>= fun () -> Facility.create db
+
+let main () =
+  Pgx_async.with_conn
+  @@ fun db ->
+  setup db
+  >>= fun () ->
+  Employee.insert ~name:"Steve" db
+  >>= fun steve_id ->
+  (* Parallel queries are not an error, but will execute in serial *)
+  [ Facility.insert ~name:"Headquarters" ~director_id:steve_id db
+  ; Facility.insert ~name:"New Office" db
+  ]
+  |> Deferred.all
+  >>= function
+  | [ headquarters_id; new_office_id ] ->
+    Facility.all_name_and_director_name db
+    >>| List.iter ~f:(fun (name, director_name) ->
+            let director_name = Option.value director_name ~default:"(none)" in
+            printf "The director of %s is %s\n" name director_name)
+    >>= fun () ->
+    print_endline "Re-assigning Steve to the New Office";
+    Facility.reassign_director
+      db
+      ~director_id:steve_id
+      ~from_facility_id:headquarters_id
+      ~to_facility_id:new_office_id
+    >>= fun () ->
+    Facility.all_name_and_director_name db
+    >>| List.iter ~f:(fun (name, director_name) ->
+            let director_name = Option.value director_name ~default:"(none)" in
+            printf "The director of %s is %s\n" name director_name)
+  | _ -> assert false
+;;
+
+let () = Thread_safe.block_on_async_exn main