Form a text search query (tsquery) with dbcontext / ado.net

PostgresFullTextSearchApi.cs

public async Task<NpgsqlTsQuery> ToTsQuery(DbContext dbContext, string searchTerm)
{
    var connection = dbContext.Database.GetDbConnection() as NpgsqlConnection;

    await using var cmd = new NpgsqlCommand("select plainto_tsquery('english', @search_term)", connection);

    cmd.CommandType = CommandType.Text;

    if (connection!.State != ConnectionState.Open) connection.Open();
    cmd.Parameters.Add(new NpgsqlParameter("search_term", searchTerm));

    var value = await cmd.ExecuteScalarAsync();
    var tsVector = value == DBNull.Value || value == null ? null : value as NpgsqlTsQuery;

    return tsVector;
}