first commit

RS_system/Data/PostgresScalarExecutor.cs

@@ -0,0 +1,36 @@
+using System.Data;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Storage;
+using Npgsql;
+
+namespace Rs_system.Data;
+
+public static class PostgresScalarExecutor
+{
+    public static async Task<T> ExecuteAsync<T>(
+        DbContext context,
+        string sql,
+        Action<NpgsqlParameterCollection>? parameters = null
+    )
+    {
+        var conn = (NpgsqlConnection)context.Database.GetDbConnection();
+
+        if (conn.State != ConnectionState.Open)
+            await conn.OpenAsync();
+
+        await using var cmd = new NpgsqlCommand(sql, conn);
+
+        var currentTx = context.Database.CurrentTransaction;
+        if (currentTx != null)
+            cmd.Transaction = (NpgsqlTransaction)currentTx.GetDbTransaction();
+
+        parameters?.Invoke(cmd.Parameters);
+
+        var result = await cmd.ExecuteScalarAsync();
+
+        if (result == null || result == DBNull.Value)
+            throw new InvalidOperationException("La consulta escalar no devolvió ningún valor.");
+
+        return (T)Convert.ChangeType(result, typeof(T));
+    }
+}