C#•4w ago

✅ Accessing associated records through navigation properties

say I had a class like so (I'm using them with EF Core)

    public class Project
    {
        public int Id { get; set; }

        [Column(TypeName="VARCHAR(32)")]
        public string Name { get; set; }
        public bool Original { get; set; }
        public int CreatedOn { get; set; }
        public int UpdatedOn { get; set; }
        public int DeletedOn { get; set; }

        public List<FeedbackRecord> FeedbackRecords { get; set; }
        public List<ManufacturingInstructions> ManufacturingInstructions { get; set; }
        public List<ModelPrototype> ModelPrototypes { get; set; }
        public List<Sketch> Sketches { get; set; }
    }

    public class Project
    {
        public int Id { get; set; }

        [Column(TypeName="VARCHAR(32)")]
        public string Name { get; set; }
        public bool Original { get; set; }
        public int CreatedOn { get; set; }
        public int UpdatedOn { get; set; }
        public int DeletedOn { get; set; }

        public List<FeedbackRecord> FeedbackRecords { get; set; }
        public List<ManufacturingInstructions> ManufacturingInstructions { get; set; }
        public List<ModelPrototype> ModelPrototypes { get; set; }
        public List<Sketch> Sketches { get; set; }
    }

given an instance of Project, how would I go about getting the related FeedbackRecords, ManufacturingInstructions, ModelPrototypes, and Sketches? Do I have to go through dbContext? or is there a way to go straight through them model itself (kinda like the way Django does it)?

11 Replies

ero•4w ago

uhh, am i missing something? given you have an instance of Project named proj1, then you access FeedbackRecords by doing proj1.FeedbackRecords.

Angius•4w ago

You would need to load them first

enrico11011OP•4w ago

I thought they were empty until loaded?

Angius•4w ago

.Include()

ero•4w ago

that i didn't know

Angius•4w ago

Or, ideally, .Select() the exact data you need into DTOs

enrico11011OP•4w ago

ok i think i got it now. basically any db access would need to go through the dbContext, is that right?

Angius•4w ago

Well, yes Hard to get the data from database without... querying the database var post = new Blogpost() doesn't just automagically grab one from the db

enrico11011OP•4w ago

in my defense Django's ORM lets you do it straight from the model itself via something like Project.objects.all() (i'm coming from a Python background) but yeah i see how it's laid out now thanks

Angius•4w ago

Guess it uses active record or something, then But yeah, with EF you'd either include, or ideally select

var post = await _ctx.Blogposts
    .Where(p => p.Id == id)
    .Include(p => p.Category)
    .Include(p => p.Tags)
    .FirstOrDefaultAsync();

var post = await _ctx.Blogposts
    .Where(p => p.Id == id)
    .Include(p => p.Category)
    .Include(p => p.Tags)
    .FirstOrDefaultAsync();

var post = await _ctx.Blogposts
    .Where(p => p.Id == id)
    .Select(p => new BlogpostDto {
        Title = p.Title,
        Body = p.Body,
        CategoryName = p.Category.Name,
        Tags = p.Tags.Select(t => new TagDto {
            Name = t.Name,
            Color = t.Color,
        }),
        Author = $"{t.Author.FirstName} {t.Author.LastName}"
    })
    .FirstOrDefaultAsync();

var post = await _ctx.Blogposts
    .Where(p => p.Id == id)
    .Select(p => new BlogpostDto {
        Title = p.Title,
        Body = p.Body,
        CategoryName = p.Category.Name,
        Tags = p.Tags.Select(t => new TagDto {
            Name = t.Name,
            Color = t.Color,
        }),
        Author = $"{t.Author.FirstName} {t.Author.LastName}"
    })
    .FirstOrDefaultAsync();

The latter would fetch only the requested data Instead of loading everything

enrico11011OP•4w ago

ahh ok so that's how you do it. TIL thanks

Gaming

Programming

✅ Accessing associated records through navigation properties

Did you find this page helpful?