EF6和MySQL时区支持

Question

I am storing datetimes at the UTC format (using DateTime.UtcNow ) in a MySQL database. After some manipulations of the entity containing that dates, it becomes a mess.

Here is how I defined my table:

CREATE TABLE `gsrep`.`GlobalVersion` (
  [..],
  `CreationDate` TIMESTAMP NOT NULL,
  `LastUpdateDate` TIMESTAMP NOT NULL,
  [..]
);

I am running the framework .NET 4.5.2 and I mapped my database with Entity Framework 6 and Database first principle.

Here is what I am doing:

First step, create the object:

var now = DateTime.UtcNow;
var globalVersion = new GlobalVersion
{
    CreationDate = now,
    LastUpdateDate = now
};
// saving the object

Let's say it is 10:00 am in my country and I am GMT +2 . The created dates have their Kind property set to DateTimeKind.Utc and their value set to 08h00 am. In the database, the dates value are 08:00 am.

Everything is fine.

Second step, get the object:

Using another connection, when I get the object from the database, the date are set to 08:00 am but their Kind property are set to DateTimeKind.Local.

This is not totally fine, but while I am only reading the data, this is not a problem. I did not even notice it until I need to change one date.

Updating one date:

And here comes the mess. At one moment, I need to change only one date. Let's say it is now 11:00 am in my country.

// getting the object
globalVersion.LastUpdateDate = DateTime.UtcNow;
// saving the object

Once saved, the LastUpdateDate is set to 09:00 am in the database (which is fine) but the CreationDate is now set to... 11:00 am . It looks like it is set to DateTime.Now at the DbContext.SaveChangesAsync() (I am saying that because if I pause during the debug between the DateTime.UtcNow and the SaveChangesAsync instruction, the CreationDate is set to the moment I click on continue).

Absolutely nothing in my code changes the CreationDate... Before the call to DbContext.SaveChangesAsync() , the CreationDate has the unchanged expected value. Right after, the CreationDate is set to the moment I clicked on continue (only in the database, in the EF cache, the value is still the same, but at the next connection, if will take the value in the database).

I am absolutely lost with this behavior... What could cause that?

I am writing the same operations in parallel in a SQLite database (I set the DateTimeKind to Utc in the connection string, and I do not have the problem).

Answer 1

Wow... though I was creating my table with this script:

CREATE TABLE `gsrep`.`GlobalVersion` (
  [..],
  `CreationDate` TIMESTAMP NOT NULL,
  `LastUpdateDate` TIMESTAMP NOT NULL,
  [..]
);

MySQL Workbench (or MySQL ?) actually created a table like that (get it using the MySQL Workbench reverse engineering):

CREATE TABLE `GlobalVersion` (
  [..],
  `CreationDate` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  `LastUpdateDate` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
  [..]
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

It had no sense that Entity Framework update the CreationDate on his own. Finally, this as nothing to do with the DateTimeKind issue. To solved it, I follow the solution proposed in the joshp's link but with some improvements .