C#•12mo ago

✅ Combining a List inside of a Select

I have an object:

    public class BackendSuccess
    {
        [Key]
        public int id { get; set; }
        public DateTime creationDate { get; set; }
        public ICollection<Label> labels { get; set; } = new List<Label>(); // BEEEEG list of base64 encoded labels
    }

    public class BackendSuccess
    {
        [Key]
        public int id { get; set; }
        public DateTime creationDate { get; set; }
        public ICollection<Label> labels { get; set; } = new List<Label>(); // BEEEEG list of base64 encoded labels
    }

And when i want to grab them all from the database, I want them combined by creationDate using LINQ. For example: creationDate:2023-12-15, labels:[{1},{2}] and creationDate:2023-12-15, labels:[{3},{4}] would combine to create creationDate:2023-12-15, labels:[{1},{2},{3},{4}] The order of the elements in labels doesn't matter, I just want them combined.

4 Replies

Angius•12mo ago

var stuff = await _context.Labels
    .GroupBy(l => l.BackendSuccess.CreationDate)
    .Select(g => new ThingDto {
        CreationDate = g.Key,
        Labels = g.Select(l => l.Id)
    })
    .ToListasync();

var stuff = await _context.Labels
    .GroupBy(l => l.BackendSuccess.CreationDate)
    .Select(g => new ThingDto {
        CreationDate = g.Key,
        Labels = g.Select(l => l.Id)
    })
    .ToListasync();

Something like that?

UntoldTitanOP•12mo ago

Lemme try that I put that in, im just converting the DateTime to a DateOnly so that they'll actually match lol made some changes, this is what I have now @ZZZZZZZZZZZZZZZZZZZZZZZZZ,

            return await _context.Successes
                .GroupBy(l => l.creationDate)
                .Select(p => new BackendSuccess { creationDate = p.Key, labels = (ICollection<Label>)p.Select(l => l.labels) })
                .ToListAsync();

            return await _context.Successes
                .GroupBy(l => l.creationDate)
                .Select(p => new BackendSuccess { creationDate = p.Key, labels = (ICollection<Label>)p.Select(l => l.labels) })
                .ToListAsync();

(ICollection<Label>)p.Select(l => l.labels) seems to be an ICollection<ICollection<>> tho, why would that be?

Angius•12mo ago

Because each success has a collection of labels, and each group will be a collection of those collections That's why I went through label and not success You can use .SelectMany() instead of .Select() there That'll flatten it

UntoldTitanOP•12mo ago

ohhh, i didnt notice that XD ok, ty it works!! thank you so much!

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✅ Combining a List inside of a Select