Transform DateTime field to provided format in where clause

Question

I'm trying to integrate a search function in my datatable in Asp.Net Core. I load the content dynamically with a query to my MSSQL server. As the database table content will increase drastically over time I'd like to "preselect" the page result, by applying all filters directly onto the sql command (rather than using AsEnumerable and doing this on client side).

But I've ran into a problem with my datetime field (actually datetime2(7)). In my view I display this value as "ShortDateFormat <HH:mm:ss> created by admin" so for example "12/11/2024 02:40:20 created by admin".

Now I implemented a search bar and would like the entry to show up if I type "12/11" in it, but this doesn't happen.

I used this query for that:

string searchValue;
string localizedText = null; // Doesn't matter how this is filled for this problem.
IQueryable<Entity> query = Entities.Where(x => x.CreateDate.ToString() + " " + localizedText).ToLower().Contains(searchValue));

Unfortunately it seems like my client and the server use different date formats as when I search for "2024-" the entry does shows up. The ToString() method doesn't seem to support the date format parameter here, so how can I convert my server format to the format the client uses? I don't know the client format at compile time though and this should support multiple languages so I'm unsure how I can do this.

Technically I used .ToShortDateString for the view, but at least in my language it matches the <HH:mm:ss>" format so it should theoretically work. I've given up on trying to use ShortDateFormat for my query as it results in the same error as providing a format in ToString() that it could not be translated.

Answer 1

Thanks to Ralf I found the Built-In "FORMAT" method from SQL and an implementation that seems to solve my issue:

public class AppContext : DbContext
{
    [DbFunction(IsBuiltIn = true)]
    public static string FORMAT(DateTime value, string formatType, string culture)
        => throw new InvalidOperationException("Do not call this directly");

    protected override void OnModelCreating(ModelBuilder builder)
    {
        builder.HasDbFunction(typeof(AppContext)
            .GetRuntimeMethod("FORMAT", [typeof(DateTime), typeof(string), typeof(string)]));
        base.OnModelCreating(builder);
    }
}

and then my query:

string culture = CultureInfo.CurrentCulture.Name;
string datePattern = CultureInfo.CurrentCulture.DateTimeFormat.ShortDatePattern;
Entities.Where(x => (ApplicationContext.FORMAT(x.CreateDate, datePattern, culture) + " " + localizedText).Contains(searchValue);

There is likely a cleaner and better way to write this, but for the moment it is sufficient.