How to use DateTime in LINQ when it's NULL

Make Birth nullable in both the EF Core entity and the view model, then use null-conditional formatting in the view so a missing birth date renders as an empty string.

Entity and view model

A nullable SQL datetime column should map to DateTime?; EF Core treats nullable value types as optional properties and non-nullable value types as required properties.^1^

// EF Core entity mapped to mytable
public class MyTable
{
    public DateTime? Birth { get; set; }
}

// Model passed to the view
public class MyModel
{
    public DateTime? Birth { get; set; }
}

Ensure the mapped entity property is nullable—not only the projected view-model property. Otherwise, EF Core can fail while materializing the database row, before assigning the result to MyModel.^2^

The projection then remains straightforward:

var query =
    from aa in mydb.MyTable
    select new MyModel
    {
        Birth = aa.Birth
    };

Format it safely in the view

Use ?. to call ToShortDateString() only when Birth has a value, and ?? to specify what should be displayed when it is null:^3^

var dob = Model.Birth?.ToShortDateString() ?? "";

Or directly in a Razor view:

<span>@(Model.Birth?.ToShortDateString() ?? "")</span>

To display a label instead of an empty value:

<span>@(Model.Birth?.ToShortDateString() ?? "Not provided")</span>

An equivalent explicit check is:

var dob = Model.Birth.HasValue
    ? Model.Birth.Value.ToShortDateString()
    : "";

Do not use Birth.Value.ToShortDateString() without first checking HasValue; accessing Value when the nullable date is empty throws InvalidOperationException with “Nullable object must have a value.”^4^

If a missing birth date is valid business data, preserving it as null is preferable to replacing it with an arbitrary date such as DateTime.MinValue.

References

1. Entity Properties
2. LINQ returns System.Data.SqlTypes.SqlNullValueException. Why? - Microsoft Q&A
3. C# null safety
4. System.Nullable<T> structure