动态 linq 日期对比查询 asp.net 核心

Question

I have a simplified version of dynamic main query as follows:

var items = context.itemsGalore.Where(where).ToList();

The where for the Where condition is built dynamically as below.

if(compare == "Greater")
{
    where = String.Format("{0} > {1}", DueDate, DateTime.ParseExact(dtValue.ToShortDateString(), "MM/dd/yyyy", CultureInfo.InvariantCulture));                            
}
else if(compare == "Lesser")
{
    where = String.Format("{0} < {1}", field, DateTime.ParseExact(dtValue.ToShortDateString(), "MM/dd/yyyy", CultureInfo.InvariantCulture));
}

However I am getting the following error: Operator '<' incompatible with operand types 'DateTime' and 'Int32'

How do I go about fixing the issue?

Answer 1

in the code this section:

else if(compare == "Lesser")
{
    where = String.Format("{0} < {1}", field, DateTime.ParseExact(dtValue.ToShortDateString(), "MM/dd/yyyy", CultureInfo.InvariantCulture));
}

The Error is because of the data type of variable 'field' that is not DateTime.

for example run this code:

using System;
using System.Globalization;
                    
public class Program
{
    public static void Main()
    {
        var compare = "Lesser";
        var where = "";
        var DueDate = DateTime.Now;
        var dtValue = DateTime.Now;
        var field = 1;
        if(compare == "Greater")
        {
            where = String.Format("{0} > {1}", DueDate, DateTime.ParseExact(dtValue.ToShortDateString(), "MM/dd/yyyy", CultureInfo.InvariantCulture));                            
        }
        else if(compare == "Lesser")
        {
            where = String.Format("{0} < {1}", field, DateTime.ParseExact(dtValue.ToShortDateString(), "MM/dd/yyyy", CultureInfo.InvariantCulture));
        }
        
        Console.WriteLine(where);
    }
}

the output is something like this: "1 < 10/07/2021 00:00:00" and you can not use this as a where clause.