通过Entity框架插入当前数据库日期时间

Question

We want to put the current datetime into a database column.

We have a web farm where the time on the web servers can vary, we therefore need to use the datetime on the database server.

We have a database with a Not Null datetime column. This column has a default datetime of current time.

This works fine when we insert data using a SQL statement that does not include the datetime column.

From Entity Framework:

• If we define the datetime as not null , the datetime is set to low date, and low date is inserted into the database.
• If we define the datetime as null , we get an exception on the insert that the value cannot be null.

We could fix this using a database trigger that changed the datetime to current datetime if the insert value is low date.

Does anyone have a better solution?

Answer 1

As the column has a default value set by the database you can simply mark the datetime column as computed:

[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
property DateTime Date { get; set; }

or in fluent mapping

this.Property(t => t.Date)
    .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Computed);

in a EntityTypeConfiguration class, or

modelBuilder.Entity<MyClass>().Property(t => t.Date)
    .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Computed);

in an OnModelCreating override.

This will cause EntityFramework to read the value of the column at each read, insert or update of a record, but it will never set it.

Answer 2

One way is to use UTC dateTime so in C# you can use

DateTime.UtcNow

You could also set

DateTime dateTime = new DateTime();
dateTime = SqlDateTime.MinValue.Value;

You can even create extension method :

public static class DateExtension
    {
        public static DateTime SqlValidDateTime(this DateTime d)
        {
            return SqlDateTime.MinValue.Value;
        }
    }

Also for:

If we define the datetime as null, we get an exception on the insert that the value cannot be null.

You should pass instead of null ->

DbNull.Value 

and then insert should pass.