Microsoft SQL Server 数据库/Visual Studio C#：日期处理

Question

I'm trying to figure out what would be the quickest and most convenient way to grab dates from the database and parse/cast them correctly into my DAL (DataAccessLayer) methods.

The columns inside my database are of datatype date .

Specifically I have this Order class:

public int Id { get; set; }
public DateTime OrderDate { get; set; }  
public DateTime ConfirmedDeliveryDate { get; set; }  
public DateTime ShippingDate { get; set; }
public Supplier Supplier { get; set; }
public List<Product> ListOfProducts { get; set; } = new List<Product>();

And then of course I have a DAL method for, let's say, getting a list of orders from the database.

List<Order> GetAll()
{
  ... ... ...
  ... ... ...
  SqlDataReader rdr = cmd.ExecuteReader()

  while(rdr.Read())
  {
    int orderId = (int)rdr["id"];
    DateTime orderDate = ???                 // HOW TO IMPLEMENT?
    DateTime? confirmedDeliveryDate = ???    // HOW TO IMPLEMENT?
    DateTime? shippingDate = ???             // HOW TO IMPLEMENT?
    ... ...
    ... ...

  }
  ... ... ...
}

NOTE: On my web I will only need YEAR , MONTH and DAY from the above mentioned dates. Not sure if that helps you, probably not but just wanted to say.

Answer 1

A date column in sql maps to a DateTime in c# . There is no need to do any special parsing. Assuming you're using a SqlDataReader , just use SqlDataReader.GetDateTime , or if you don't know the column ordinal use the indexer and pass it the column name then cast the result to a DateTime just like you're doing with the "id" column.

DateTime orderedDate = (DateTime)rdr["orderedDate"];
// or
DateTime orderdDate = rdr.GetDateTime(/*column ordinal*/)

If the date columns in the database are nullable, then you need to account for that in your code by making the DateTime objects nullable ( DateTime? ) and checking for null when reading the results from the SqlDataReader .

List<Order> GetAll()
{
    SqlDataReader rdr = cmd.ExecuteReader()
    while(rdr.Read())
    {
        int orderId = (int)rdr["id"];
        DateTime? orderedDate = null;
        if (rdr["orderedDate"] != DBNull.Value)
        {
            orderedDate = (DateTime)rdr["orderedDate"];
        }
    }
}

You could put this into an extension method on SqlDataReader if you wanted...

public static class SqlDataReaderExtensions
{
    public static DateTime? GetNullableDateTime(this SqlDataReader rdr, string columnName)
    {
        if (rdr[columnName] != DBNull.Value)
        {
            return (DateTime)rdr[columnName];
        }
        return null;
    }
}

List<Order> GetAll()
{
    SqlDataReader rdr = cmd.ExecuteReader()
    while(rdr.Read())
    {
        int orderId = (int)rdr["id"];
        DateTime? orderedDate = rdr.GetNullableDateTime("ordredDate");
    }
}

If your view only needs to display the year, month, and day then you can do that in several ways. For example, DateTime.ToShortDateString or DateTime.ToString(string) .