How to set DateTime equals method with Dynamic Linq in C#?

Question

I need to filter data with Dynamic LINQ by DateTime field.

I'm try doing this like:

public class MyClass
{
    private DateTime datetime_field;
    //...
    //some other fields
    //...
}

public void MyMethod(string where_clause)
{
    List<MyClass> myData = new List<MyClass>()
    {
        //...
        //initialization
        //...
    };
    var query = myData.Where(where_clause).ToList();
    myDataGridView.DataSource = query;
}

// usage
string value = DateTime.Now.ToString(); // for example
if (DateTime.TryParse(value, out DateTime dt))
    MyMethod("datetime_field == DateTime(" + dt.Year + ", " + dt.Month + ", " + dt.Day + ", " + dt.Hour + ", " + dt.Minute + ", " + dt.Second + ")");

But the query return zero records. But if i set compare method >= or <= instead ==, query returns needed records amount.
Maybe I'm doing something wrong?

UPDATE:
I found example here: https://stackoverflow.com/a/26450835/7760805, but I'm still search a better solution.

UPDATE:
Solved by Stef Heyenrath.

DateTimes are precise way below the level of a second. Try throw away the milliseconds part of your datetime_field — Flydog57, Aug 22 '19 at 23:32
@Flydog57, thanks, it's realy may help me. But how can I ignore milliseconds of my datetime_field with Dynamic LINQ? — Vlad i Slav, Aug 23 '19 at 01:01

Cameron Wilby · Answer 1 · 2019-08-23T12:40:41.207

3

You should pass a string into the MyMethod method, then convert to DateTime and remove milliseconds within the method.

public class MyClass
{
    public DateTime datetime_field; // note this needs to be public, not private
}

public void MyMethod(string strDate)
{
    if (DateTime.TryParse(value, out DateTime dt))
    {
        List<MyClass> myData = new List<MyClass>()
        {
            // initialization
        };

        var roundedDate = new DateTime(dt.Year, dt.Month, dt.Day,
                                       dt.Hour, dt.Minute, dt.Second);

        var query = myData.Where(obj => obj.date_time == roundedDate).ToList();

        myDataGridView.DataSource = query;   
    }
}

// usage
string value = DateTime.Now.ToString();
MyMethod(value);

edited Aug 23 '19 at 12:40

answered Aug 22 '19 at 21:53

Cameron Wilby

2,222
1
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Thanks, but this solution will crash all logic of my application. I need that parameter of `MyMethod` will be `string` type. – Vlad i Slav Aug 23 '19 at 01:12
1

@VladiSlav Updated to match your logic. In my opinion, MyMethod should accept a DateTime object and chop milliseconds there. – Cameron Wilby Aug 23 '19 at 12:35
I need to use Dynamic LINQ because I have several fields in MyClass, which besides DateTime can be string, int, etc. So `MyMethod` need to take **where clause** as string, not value for search. – Vlad i Slav Aug 23 '19 at 13:17

score 3 · Accepted Answer · answered Aug 23 '19 at 19:19

3

Depending on the accuracy you need, you could just use the >= and < operators together, like this:

var date = DateTime.Now;

// accuracy is 1 day in this example
var from = date.Date;
var to = from.AddDays(1);

// If you only need to select on a day, use this:
var result = query.Where("datetime_field >= @0 && datetime_field < @1", from, to);

answered Aug 23 '19 at 19:19

Stef Heyenrath

9,335
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Thanks a lot! This is exactly what I need! – Vlad i Slav Aug 23 '19 at 19:33

score -1 · Answer 3 · answered Aug 23 '19 at 10:32

-1

What is the content of MyMethod ?

Try using the $ string builder.

MyMethod($"datetime_field == {new DateTime(dt.Year, dt.Month, dt.Day, dt.Hour, dt.Minute , dt.Second)}");

OR

MyMethod($"datetime_field == {dt.ToString())}");

I think its a problem with your logic not how you are constructing or passing datetime parameter.

answered Aug 23 '19 at 10:32

Gabriel Scavassa

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Sorry, but this way calling an error: "Syntax error '{' ". – Vlad i Slav Aug 23 '19 at 13:04
@VladiSlav hm. I think its a old version of C# – Gabriel Scavassa Aug 26 '19 at 06:56
That is weird, You must be able to use $"". https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/tokens/interpolated – Gabriel Scavassa Aug 28 '19 at 13:42

How to set DateTime equals method with Dynamic Linq in C#?

3 Answers3