How to order by week number in Entity Framework Core?

Question

I need to OrderBy the DbSet by number of the week in the year. Like iso_week datepart in T-SQL (https://learn.microsoft.com/en-us/sql/t-sql/functions/datepart-transact-sql?redirectedfrom=MSDN&view=sql-server-ver16#iso_week-datepart).

It is possible to use SqlFunctions.DatePart() in Entity Framework 6, however, there is no such method in EF Core.

So how can I use LINQ's OrderBy with WeekOfYear in EF core?

Check [SqlFunctions.DatePart equivalent in EF Core](https://stackoverflow.com/questions/52529454/sqlfunctions-datepart-equivalent-in-ef-core) — T. Dominik, Oct 17 '22 at 11:01

DavidG · Answer 1 · 2022-10-17T11:29:04.430

It's not built into EF Core by default, but you can create your own function mapping. Assuming this is in .NET 6, you can do something like this:

public class MyDbContext : DbContext
{
    //snip other stuff

    // Add a stub method we can use later...
    public int? DatePart(string datepart, DateTime? date) => throw new NotImplementedException();

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        // Get a reference to the stub method
        var methodInfo = typeof(MyDbContext)
            .GetRuntimeMethod(nameof(DatePart), new[] { typeof(string), typeof(DateTime?) });

        // Now tell the context how to map the stub method to the actual SQL
        builder
            .HasDbFunction(methodInfo)
            .HasTranslation(args =>
            {
                var datepartFragment = new SqlFragmentExpression(((SqlConstantExpression)args[0]).Value.ToString());
                var datePropertyFragment = new SqlFragmentExpression(((ColumnExpression)args[1]).Name);

                return new SqlFunctionExpression(
                    nameof(DatePart),
                    new SqlExpression[] { datepartFragment, datePropertyFragment },
                    true,
                    new[] { true, true },
                    typeof(int?),
                    RelationalTypeMapping.NullMapping
                );
            });
    }

}

Now you can call this method in your Linq queries like this:

var products = _context.Products
    .Select(p => new 
    {
        Name = p.Name,
        IsoWeekCreated = _context.DatePart("iso_week", p.DateCreated) // <--- The clever bit here
    })
    .ToList();

How to order by week number in Entity Framework Core?

1 Answers1