Dynamic Linq Query not working with DateTime field

Question

I am using Dynamic linq to provide my MVC app with data and I have trouble with DateTime fields.

The objects I'm parsing through has a System.Datetime field and I want to check if the dates correspond.

So I try to build the string like this (I'm parsing through a dynamic dictionary to get the data):

string dateToParse = keyValuePair.Value;

DateTime objDate = DateTime.Parse(dateToParse);

valuesToUse.Add("OBJ_DATE.Date == " + objDate.ToShortDateString());

And when I load the data, I do it like this:

var objQry = from pl in m_Db.OBJS.Where(whereConditions)
                               select pl;

The whereConditions variable is a string I build when I have all the data.

But when the data hits the datetime field, the app crashes with the following statement:

Operator '==' incompatible with operand types 'DateTime' and 'Int32'

How can I check a DateTime field using dynamic Linq? I have tried many options, like putting the objDate without ToShortDateString, but with the same effect.

EDIT:

"OBJ_DATE.Date == 2012.01.01", for example

Your two code samples appear to have nothing to do with each other. — Bobson, Apr 25 '13 at 20:40
And I'm using dynamic query for my app, which worked quite nice up to now — hsim, Apr 25 '13 at 20:44

score 3 · Answer 1 · answered Apr 25 '13 at 20:45

3

Convert your date to an actual date object and use the Compare() method.

http://msdn.microsoft.com/en-us/library/system.datetime.compare.aspx

Or, you can convert both to a long and compare them that way. You're trying to compare an object to a literal.

Edit: You could also convert them both to strings and compare. The important thing is you're comparing apples to apples. Not apples to Date objects. =)

answered Apr 25 '13 at 20:45

Yatrix

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How do you do this with dynamic linq and a string? – hsim Apr 25 '13 at 20:58
I mean, I do understand what you are saying, but I need to format the string so that the dynamic linq knows what I'm asking out of it... – hsim Apr 25 '13 at 20:59
@HerveS I'm not sure. I've never tried linq like that, but if it's just reading that string as code, then you can probably do *DateTime.Compare(OBJ_Date.Date, DateTime.Parse("2012.01.01"))*. The result of compare is an int and 0 means they're equal. – Yatrix Apr 25 '13 at 21:02
1

@HerveS I found this as well, which may be helpful: http://stackoverflow.com/questions/2818044/linq-to-sql-dynamic-query-with-date-type-fields/6291803#6291803 – Yatrix Apr 25 '13 at 21:06

Nick Albrecht · Answer 2 · 2013-04-25T22:25:45.597

Maybe I'm missing something but don't you have to wrap your date in quotes or something to get it to treat it as a date? I'm trying to remember how the Dynamic Linq works but there must be some way of telling the extension methods that your criteria isn't a primitive type?

OBJ_DATE.Date == "2012.01.01"

UPDATE - Ah ha I knew that code looked funny. Try passing it as a parameter to the extension method rather than trying to do it as one inline string. I was able to come up with this, but I couldn't spend any more time on it. So you'll have to do some digging on how to combine multiple expressions so that you can build them up dynamically the way you say you're doing it in your question.

This is a Copy & Paste from LinqPad

public void Main()
{
    var people = new List<Person>()
    {
        new Person(){Name = "Jpe", BirthDate =DateTime.Parse("March 18, 1980")},
        new Person(){Name = "Bob", BirthDate =DateTime.Parse("July 22, 1989")},
        new Person(){Name = "Sarah", BirthDate =DateTime.Parse("Nov 5, 1995")}
    };

    var firstExpression = System.Linq.Dynamic.DynamicExpression.ParseLambda<Person, bool>("BirthDate = @0", DateTime.Parse("July 22, 1989"));
    //var secondExpression = System.Linq.Dynamic.DynamicExpression.ParseLambda<Person, bool>("Name = @0", "Nick");
    //var finalExpression = Expression.And(firstExpression, secondExpression);
    people.AsQueryable().Where(firstExpression).FirstOrDefault().Dump();
}

public class Person
{
    public string Name{get;set;}
    public DateTime BirthDate {get;set;}
}

Nope, I've tried writing valuesToUse.Add("OBJ_DATE.Date == \"" + objDate + "\"");` and the same error occurs again. — hsim, Apr 25 '13 at 20:56

Dynamic Linq Query not working with DateTime field

EDIT:

2 Answers2