You should only set a property of a temporal type (like DateTime or DateTimeOffset) as the primary key of a table if the values are guaranteed to be unique.

Why is this an issue?

Using temporal types as the primary key of a table is risky. When these types are used as primary keys, it usually means that each new key is created with the use of .Now or .UtcNow properties from DateTime and DateTimeOffset classes. In those cases, duplicate keys exceptions may occur in many ways:

• when entries are added consecutively by a machine with low-enough system clock resolution;
• when two different threads are inserting entries in close enough sequence for both to have the same time;
• when changes such as daylight saving time (DST) transitions occur, where values can be repeated the following hour (only for DateTime type);

The rule raises an issue if:

• Entity Framework, or Entity Framework Core dependencies are found;
• a class contains a property either named Id, <type name>Id or decorated by the [Key] or [PrimaryKey] attribute.
• the key property is of one of the following types:
  • System.DateTime
  • System.DateTimeOffset
  • System.TimeSpan
  • System.DateOnly
  • System.TimeOnly

How to fix it

Either use a GUID or the auto generated ID as a primary key.

Code examples

Noncompliant code example

Public Class Account
    Public Property Id As DateTime

    Public Property Name As String
    Public Property Surname As String
End Class

Compliant solution

Public Class Account
    Public Property Id As Guid

    Public Property Name As String
    Public Property Surname As String
End Class

or

Noncompliant code example

Public Class Person
    <Key>
    Public Property PersonIdentifier As DateTime

    Public Property Name As String
    Public Property Surname As String
End Class

Compliant solution

Public Class Person
    <Key>
    Public Property PersonIdentifier As Guid

    Public Property Name As String
    Public Property Surname As String
End Class

Resources

Documentation

• Entity Framework keys and data annotation
• GUID