如何在asp.net web API中从postgresql数据库读取数据

// 数据访问层
public class DataAccessLayer
{
    private readonly string connectionString;

    public DataAccessLayer(string connectionString)
    {
        this.connectionString = connectionString;
    }

    public IEnumerable<Customer> GetCustomers()
    {
        using (var connection = new NpgsqlConnection(connectionString))
        {
            connection.Open();
            var query = "SELECT * FROM customers";
            return connection.Query<Customer>(query);
        }
    }
}

// 控制器
public class CustomersController : ApiController
{
    private readonly DataAccessLayer dataAccessLayer;

    public CustomersController()
    {
        var connectionString = ConfigurationManager.ConnectionStrings["PostgreSQLConnection"].ConnectionString;
        dataAccessLayer = new DataAccessLayer(connectionString);
    }

    public IHttpActionResult GetCustomers()
    {
        var customers = dataAccessLayer.GetCustomers();
        return Ok(customers);
    }
}

// 数据模型
public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
    // 其他属性...
}