Translate to PostgreSQL date_trunc

date_trunc('week', now()::date

Looking to make a call similar to this, and can’t figure out what should be used now. I’ve also looked at EF.Property<DateTime>() but that doesn’t seem to help.

[roji]

The provider does translate certain expressions with date_trunc (e.g. DateTime.Date gets translated to date_trunc('day', ...), but there’s no general .NET method which is the equivalent of PostgreSQL date_trunc. We could add a translation for this under EF.Functions.

In the meantime you can map it via your own DbFunction mapping:

class Program
{
    static async Task Main(string[] args)
    {
        await using var ctx = new BlogContext();
        await ctx.Database.EnsureDeletedAsync();
        await ctx.Database.EnsureCreatedAsync();

        _ = ctx.Blogs.Where(b => BlogContext.DateTrunc("weeks", b.Creation) == new DateTime(2000, 1, 1)).ToList();
    }
}

public class BlogContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }

    static ILoggerFactory ContextLoggerFactory
        => LoggerFactory.Create(b => b.AddConsole().AddFilter("", LogLevel.Information));

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseNpgsql(@"Host=localhost;Username=test;Password=test")
            .EnableSensitiveDataLogging()
            .UseLoggerFactory(ContextLoggerFactory);

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.HasDbFunction(DateTruncMethod).HasName("date_trunc");
    }

    private static readonly MethodInfo DateTruncMethod
        = typeof(BlogContext).GetRuntimeMethod(nameof(DateTrunc), new[] { typeof(string), typeof(DateTime) });

    public static DateTime DateTrunc(string field, DateTime source)
        => throw new NotSupportedException();
}

public class Blog
{
    public int Id { get; set; }
    public DateTime Creation { get; set; }
}

[FossaMalaEnt]

I’m using it on a “.GroupBy()” and it don’t work.

public class MyContext : DbContext
{
    public DbSet<MyEntity> MyEntities { get; set; }

    public MyContext (DbContextOptions<MyContext> options) : base(options) { }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.HasDbFunction(DateTruncMethod).HasName("date_trunc");

        modelBuilder.Entity<MyEntity>().ToTable("TableName");
    }
    
    private static readonly MethodInfo DateTruncMethod
        = typeof(MyContext).GetRuntimeMethod(nameof(DateTrunc), new[] { typeof(string), typeof(DateTime) });

    public static DateTime DateTrunc(string field, DateTime source)
        => throw new NotSupportedException();
}

LINQ

        var q = this_context.MyEntities.Where(x => x.mac.Equals("address"));
        var qualcosa = await q.GroupBy(x => MyContext.DateTrunc("minute", x.Created))
                                 .Select(x => new ResultDTO()
                                 {
                                     Date = x.Key.ToString(),
                                     Average = x.Average(y => y.Value)
                                 })
                                 .ToListAsync();

But i get

The LINQ expression ‘DbSet<MyEntity>() .Where(x => x.Mac.Equals(“address”)) .GroupBy(x => MyContext.DateTrunc(field: “hour”, source: x.Created))’ could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to ‘AsEnumerable’, ‘AsAsyncEnumerable’, ‘ToList’, or ‘ToListAsync’. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.

It fails on the groupBy, I know cause I’ve tried commenting the Select and fails anyway, but if I comment also the groupBy then it works.