C#•8mo ago

❔ EFCore Change Tracker Confusion

Assuming a entity Order with a relationship to entity Table

var order = new Order() {
   ...
   TableId = requestTableId
};
db.Orders.Add(order);
await db.SaveChangesAsync();

var sameOrder = await db.Orders.Include(o => o.Table).Where(o => order.Id).SingleAsync();

var order = new Order() {
   ...
   TableId = requestTableId
};
db.Orders.Add(order);
await db.SaveChangesAsync();

var sameOrder = await db.Orders.Include(o => o.Table).Where(o => order.Id).SingleAsync();

Shouldn't the "sameOrder" be fetched from the tracker and do a single query for the table only? Since it's already being tracked.. Because in my application I'm seeing it fetches the whole order from the start... Unless there's some kinda of rule about relationships that I couldn't find

12 Replies

UltraWelfare•8mo ago

Seems like the answer relies here

Jimmacle•8mo ago

what if the order was modified in the database between saving it and getting it back? the change tracker tracks local modifications, it's not a caching layer per se

UltraWelfare•8mo ago

I read somewhere that reading an entity that already exists in the changetracker, returns the entity from the changetracker that is especially true with the "Include" there's a pitfall too Seems like it only works with Find

    public class Order
    {
        public int Id { get; set; }
        public string Title { get; set; }
        
        public int TableId { get; set; }
        public Table Table { get; set; }
    }
    
    public class Table
    {
        public int Id { get; set; }
        public string Title { get; set; }
        
        public List<Order> Orders { get; set; } = new();
    }

    public class TestContext : DbContext
    {
        public TestContext(){ }

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

        public DbSet<Order> Orders { get; set; }
        
        public DbSet<Table> Tables { get; set; }
    }
    
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("This is an example of using EF Core InMemory Database");
            Console.WriteLine("======================================================");
            Console.WriteLine("");
            
            var options = new DbContextOptionsBuilder<TestContext>()
                .UseSqlite("DataSource=test.db")
                .LogTo(Console.WriteLine)
                .Options;
            var ctxOld = new TestContext(options);
            ctxOld.Database.EnsureCreated();
            
            ctxOld.Tables.Add(new Table() { Id = 1, Title = "a" });
            ctxOld.SaveChanges();
            ctxOld.Dispose();
            
            var ctx = new TestContext(options);
            
            var order = new Order() {
                Title = "Order Title",
                TableId = 1
                
            };
            
            ctx.Orders.Add(order);
            ctx.SaveChanges();
            
            ctx.Orders.Single(o => o.Id == 1);
            ctx.Orders.Single(o => o.Id == 1);
        }
    }

    public class Order
    {
        public int Id { get; set; }
        public string Title { get; set; }
        
        public int TableId { get; set; }
        public Table Table { get; set; }
    }
    
    public class Table
    {
        public int Id { get; set; }
        public string Title { get; set; }
        
        public List<Order> Orders { get; set; } = new();
    }

    public class TestContext : DbContext
    {
        public TestContext(){ }

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

        public DbSet<Order> Orders { get; set; }
        
        public DbSet<Table> Tables { get; set; }
    }
    
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("This is an example of using EF Core InMemory Database");
            Console.WriteLine("======================================================");
            Console.WriteLine("");
            
            var options = new DbContextOptionsBuilder<TestContext>()
                .UseSqlite("DataSource=test.db")
                .LogTo(Console.WriteLine)
                .Options;
            var ctxOld = new TestContext(options);
            ctxOld.Database.EnsureCreated();
            
            ctxOld.Tables.Add(new Table() { Id = 1, Title = "a" });
            ctxOld.SaveChanges();
            ctxOld.Dispose();
            
            var ctx = new TestContext(options);
            
            var order = new Order() {
                Title = "Order Title",
                TableId = 1
                
            };
            
            ctx.Orders.Add(order);
            ctx.SaveChanges();
            
            ctx.Orders.Single(o => o.Id == 1);
            ctx.Orders.Single(o => o.Id == 1);
        }
    }

using linq operators will always do a db roundtrip even with or without include

Jimmacle•8mo ago

yes, i wouldn't want it to work any other way

UltraWelfare•8mo ago

it works like that on include though thats strange if you query something and include orderby then query it again and do the same thing the include will not work

Jimmacle•8mo ago

define "not work"

UltraWelfare•8mo ago

literally, it will ignore it it's in the ms documentation https://learn.microsoft.com/en-us/ef/core/querying/related-data/eager#filtered-include look at Caution

var orders = context.Orders.Where(o => o.Id > 1000).ToList();

// customer entities will have references to all orders where Id > 1000, rather than > 5000
var filtered = context.Customers.Include(c => c.Orders.Where(o => o.Id > 5000)).ToList();

var orders = context.Orders.Where(o => o.Id > 1000).ToList();

// customer entities will have references to all orders where Id > 1000, rather than > 5000
var filtered = context.Customers.Include(c => c.Orders.Where(o => o.Id > 5000)).ToList();

Jimmacle•8mo ago

i have never used a filtered include

UltraWelfare•8mo ago

yeah I accidently did it... and then I assumed tracked entities are always returned Stay away from it

Jimmacle•8mo ago

yeah that syntax is wrong if you're just trying to get orders nvm, read wrong syntax is still wrong either way

UltraWelfare•8mo ago

Yep, in my case when i did a filtered include i was trying just to orderby the collection but it didn't work and it was this " bug " so I assumed changetracker always returns the tracked entities seems like not the case unless you're using Find(key) this seems to always return the tracked entity if found anything else just does a db roundtrip

Accord•8mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ EFCore Change Tracker Confusion