Harald Coppoolse Harald Coppoolse - 10 months ago 99
C# Question

Entity Framework Code First: which DataType attribute for DateTime2?

Sometime when using Entity Framework Code First, the default conventions do not create the database type you want. For instance by default a property of type System.DateTime gets a database column of datetime. But what to do if you want it to have a type of datetime2 (the datetime type that has no problems with time zones and daylight saving time)?

Luckily if is possible to specify the required database type using the DataTypeAtrribute. One of the constructors of DataTypeAttribute accepts a parameter DataType Enumeration. So one could specify something like:

public DateTime DateOfBirth {get; set;}

The DataType enumeration type contains a lot of types, however it is missing a value for DateTime2.

It is possible to create a DateTime2 via the method DBContext.OnModelCreating:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
modelBuilder.Entity<Student>().Property(p => p.BirthDate)

The DataTypeAttribute has a second constructor that accepts a string, where the string is defined:

The name of the custom field template to associate with the data field.

So one would assume that the following would be enough to create a datetime2:

public DateTime DateOfBirth {get; set;}

Alas, this doesn't work. The created column has the datetime format.

Question: which string to use in the constructor to create a datetime2?

Answer Source

The DataType attribute is not used for column type mapping for Code First:

The Column annotation is a more adept in specifying the attributes of a mapped column. You can stipulate a name, data type or even the order in which a column appears in the table. [...] Don’t confuse Column’s TypeName attribute with the DataType DataAnnotation. DataType is an annotation used for the UI and is ignored by code first.