C# Nullable DateTime Formatting Error - Cannot implicitly convert type 'string' to 'System.DateTime?'

Question

I have a nullable datetime column in my database.

In my viewmodel I have this property defined as follows:

public DateTime? ExpiryDate { get; set; }

In my controller edit method I am trying to set the value of this property as follows:

 viewModel.ExpiryDate = topic.ExpiryDate.HasValue ?
          topic.ExpiryDate.Value.ToString("DD MMM YYYY") : null;

But I'm getting error:

 Cannot implicitly convert type 'string' to 'System.DateTime?'

If I have the following i.e non nullable, it works fine without any errors:

 public DateTime ExpiryDate { get; set; }

 viewModel.ExpiryDate = topic.ExpiryDate.ToString("DD MMM YYYY")

viewModel.ExpiryDate is a DateTime? but you're trying to assign a string. Isn't it clear? A DateTime has no format, what are you trying to achieve with ToString("DD MMM YYYY") here? — Tim Schmelter
– Tim Schmelter, Commented Jun 16, 2016 at 8:00
Clearly ExpiryDate should be assigned as Convert.ToDateTime(string format) or DateTime.ParseExact(string format). — Tetsuya Yamamoto
– Tetsuya Yamamoto, Commented Jun 16, 2016 at 8:01
ExpiryDate is a nullable DateTime value in my database table. In my view I want to format its display inside a textbox field. That is why i'm trying to format it when I assign it the the viewmodel. — adam78
– adam78, Commented Jun 16, 2016 at 8:21

Dr. Stitch · Accepted Answer · 2016-06-16 08:01:39Z

3

do this:

viewModel.ExpiryDate = topic.ExpiryDate.HasValue ?
          topic.ExpiryDate.Value : null;

With this code .ToString("DD MMM YYYY"), you're passing a string to a DateTime type property. Please make sure viewModel.ExpiryDate is also a nullable DateTime type since you're trying to assign a null value.

answered Jun 16, 2016 at 8:01

Dr. Stitch

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4 Comments

fubo Over a year ago

why not directly viewModel.ExpiryDate = topic.ExpiryDate?

Dr. Stitch Over a year ago

not sure what is the type of both but you're correct fubo. :)

Tetsuya Yamamoto Over a year ago

Convert.ToDateTime(String.Format("{0:dd MMM yyyy}", topic.ExpiryDate.Value) or DateTime.ParseExact(topic.ExpiryDate.Value, "dd MMM yyyy", CultureInfo.InvariantCulture) are possible if OP requires certain date format, i.e. topic.ExpiryDate is a string and not DateTime.

adam78 Over a year ago

@ Tetsuya topic.ExpiryDate is a datetime value which can be nullable.

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