MySqlConnector


DateTime Storage

MySQL cannot store all the information from a DateTime or DateTimeOffset value, so the following considerations should be kept in mind when storing DateTime and DateTimeOffset values in MySQL DATETIME or TIMESTAMP columns.

MySQL Column Types

There are two MySQL column types for date values: TIMESTAMP and DATETIME.

The MySQL documentation should be consulted to understand the behavior of these two column types, particularly around:

  • Range: 1970-01-01 00:00:01 to 2038-01-19 03:14:07 for TIMESTAMP; 1000-01-01 to 9999-12-31 for DATETIME.
  • Time zones: TIMESTAMP values will be converted to UTC for storage and from UTC for retrieval, which can lead to reading different values.

Range and DateTime.MinValue/MaxValue

DateTime.MinValue and DateTime.MaxValue both exceed the range of a DATETIME column (and are well outside the range of a TIMESTAMP column).

DateTime.MinValue is 0001-01-01 00:00:00, but the minimum supported value for a DATETIME column is 1000-01-01 00:00:00. In many versions of MySQL Server, you can successfully insert this value; however, it is not officially supported.

By default, inserting DateTime.MaxValue into a DATETIME column will fail with a “datetime field overflow” error, because the timestamp is 23:59:59.9999999 but DATETIME can’t store fractional seconds. To fix this, declare the column as DATETIME(6).

DateTime Notes

The DateTime.Kind property cannot be round-tripped. By default, all DateTime values read from MySQL will have a Kind property of DateTimeKind.Unspecified.

A best practice is to ensure that only UTC values are stored in a DATETIME column, to avoid data loss when reading or comparing values across different timezones. To enforce this, set DateTimeKind=Utc in the connection string. When this is set, all values will be retrieved as DateTimeKind.Utc, and it is an error to insert DateTimeKind.Local values.

Conversely, this connection string option can also be set to DateTimeKind=Local to force the storage and retrieval of only local values.

DateTimeOffset Notes

It is not possible to store a DateTimeOffset in a DATETIME column. If you create a MySqlParameter with a Value holding a DateTimeOffset, only the UtcDateTime property will be stored in MySQL. The recommended approach to store and retrieve DateTimeOffset values is to use two columns: one for the LocalDateTime and one for the Offset.

DateTimeOffset Table Schema

CREATE TABLE times (
    LocalDateTime DATETIME(6),
    Offset TIME
);

Storing a DateTimeOffset

DateTimeOffset dto;
using var cmd = connection.CreateCommand();
cmd.CommandText = "insert into times(LocalDateTime, Offset) values(@LocalDateTime, @Offset);";
cmd.Parameters.AddWithValue("@LocalDateTime", dto.LocalDateTime);
cmd.Parameters.AddWithValue("@Offset", dto.Offset);
cmd.ExecuteNonQuery();

Reading a DateTimeOffset

using var cmd = connection.CreateCommand();
cmd.CommandText = "select LocalDateTime, Offset from times;";
using var reader = cmd.ExecuteReader();
while (reader.Read())
{
    var dto = new DateTimeOffset(reader.GetDateTime(0), reader.GetTimeSpan(1));
}