How can I serialize DateTime values as `yyyy-MM`?

Question

In an ASP.NET MVC application, I get the date from the database in this way:

public class MonthController : ApiController

{
    public List<Month> monthContainer;

    public List<Month> getMonth()
    {
        DataContext dataContext = new DataContext();

        monthContainer = (from d in dataContext.Duties
                          select new Month()
                          {
                              MonthDate = d.Date
                          }).ToList();
        return monthContainer;
    }

In the answer comes a date in this format:

{
    "MonthDate": "2015-10-01T00:00:00"
},
{
    "MonthDate": "2015-10-02T00:00:00"
}

And so it goes every day of the month MonthDate until a certain year. How can I withdraw only months in this format without doubles? How to make a change in the controller? I want to get this format:

    "MonthDate": "2015-10"
    "MonthDate": "2015-11"
    "MonthDate": "2015-12"
    "MonthDate": "2016-01"
... "MonthDate": "2019-12"

Dates have no format. They are binary values. Formats are used *only* when text is parsed into a date, or a date is formatted as a text for display. Wherever you display those dates, add a format string or a call to `ToString` or `String.Format` with the format you want — Panagiotis Kanavos, Nov 21 '19 at 10:27
How do you display those dates? That's where you need to use formatting. At the very least post the relevant view code — Panagiotis Kanavos, Nov 21 '19 at 10:27
You can use the [DisplayFormat](https://learn.microsoft.com/en-us/dotnet/api/system.componentmodel.dataannotations.displayformatattribute?view=netframework-4.8) attribute to tell MVC how to format specific fields. You could add `[DisplayFormat(DataFormatString = "{0:yyyy-MM}")]` to the `MonthDate` property — Panagiotis Kanavos, Nov 21 '19 at 10:33
You may need to change `MonthDate` property of the `Month` class to string type. then you may use the following code. monthContainer = (from d in dataContext.Duties select new Month() { MonthDate = d.Date.ToString("yyyy-MM", CultureInfo.InvariantCulture) }).ToList(); because `date` type does not have any format it is a binary value which you may format when converting to string. — Mukul Keshari, Nov 21 '19 at 10:33
@MukulKeshari there's no reason for this. All UI stacks, whether web or desktop, offer ways to format data. — Panagiotis Kanavos, Nov 21 '19 at 10:34
Guys, I write only the backend and want to format the date in the controller. Model - public class Month { public DateTime MonthDate { get; set; } } — just, Nov 21 '19 at 10:44
@just did you try adding the `DisplayFormat` attribute ? That's the easiest way for the backend to affect how the *front*end renders data. — Panagiotis Kanavos, Nov 21 '19 at 10:53
@just wait, are you asking about *JSON serialization* in Web API? That's a *very* different question, already supported by JSON.NET through custom converters. The second duplicate shows how to create a custom date converter. Change the `DateTimeFormat` to `yyyy-MM` and add `[Newtonsoft.Json.JsonConverter(typeof(CustomDateTimeConverter))]` to the `MonthDate` property. The result will be `{"MonthDate":"2019-11"}` — Panagiotis Kanavos, Nov 21 '19 at 11:03
@Panagiotis Kanavos, I get a response in JSON, sorry, not indicated. I do not quite understand how to apply the solution with [Newtonsoft.Json.JsonConverter (typeof (CustomDateTimeConverter))] — just, Nov 21 '19 at 11:10
Did you read the duplicate? Create the converter class shown there, use the custom format and apply the converter. You'll find more examples at [JSON.NET's doc site](https://www.newtonsoft.com/json/help/html/JsonConverterAttributeClass.htm). JSON.NET converts data to JSON and vice versa using converters. You can create your own converters to change how the conversion works, use different formats etc. — Panagiotis Kanavos, Nov 21 '19 at 11:11
@Panagiotis Kanavos, hi! Solution from a duplicate helped me, I created new classes in the model, and they converted my JSON, thx u! — just, Nov 22 '19 at 06:04

score -1 · Answer 1 · answered Nov 21 '19 at 10:21

-1

Please, use DateTime.ParseExact like this :

DateTime.ParseExact(MonthDate.ToString(), "yy/MM/dd HH:mm:ss", 
    CultureInfo.InvariantCulture
    ).ToString("yyyy-MM")

answered Nov 21 '19 at 10:21

ChillAndCode

188
2
12

Hi! Tell me, please, in which part of the code will this code be added correctly? – just Nov 21 '19 at 10:26
@just none - both answers are wrong. Dates get formatted in the *view*, not the query. Post your view code – Panagiotis Kanavos Nov 21 '19 at 10:29
The OP asks about formatting, not parsing. The string doesn't match `yy/MM/dd HH:mm:ss` anyway. Besides, if `MonthDate` is *already* a date, what's the point of parsing? – Panagiotis Kanavos Nov 21 '19 at 10:29

score -1 · Answer 2 · answered Nov 21 '19 at 10:22

-1

you have to use parseExact method like:

MonthDate = DateTime.ParseExact(d.Date, "yyyy-MM",CultureInfo.InvariantCulture);

Some Documentation: https://learn.microsoft.com/en-us/dotnet/api/system.datetime.parseexact?view=netframework-4.8

answered Nov 21 '19 at 10:22

Pugnatore

395
3
19

The OP asks about formatting, not parsing. The string doesn't match `yyyy-MM` anyway – Panagiotis Kanavos Nov 21 '19 at 10:29
He is not asking for formating or parsing, he only said he wants to CONVERT the date in a specific format – Pugnatore Nov 21 '19 at 10:41
That's what formatting means. Even in SQL, `CONVERT` formats non-text values to string with predefined formats – Panagiotis Kanavos Nov 21 '19 at 10:47

How can I serialize DateTime values as `yyyy-MM`?

2 Answers2