C#•2y ago

❔ EntityFramework does not track changes for the select projection

Hey, With Select (), I only extracted the data I needed, which I want to update later. However, after SaveChanges () is executed, the value in DB does not change.

var product = await _dbContext.Products
                .Include(x => x.Additionals)
                .Where(p => p.Id == Id)
                .Select(x => new Product { Id = x.Id, Name = x.Name, Additionals = x.Additionals })
                .SingleOrDefaultAsync();

product.Name = "ChangedName";
await _dbContext.SaveChangesAsync();   //no database changes

var product = await _dbContext.Products
                .Include(x => x.Additionals)
                .Where(p => p.Id == Id)
                .Select(x => new Product { Id = x.Id, Name = x.Name, Additionals = x.Additionals })
                .SingleOrDefaultAsync();

product.Name = "ChangedName";
await _dbContext.SaveChangesAsync();   //no database changes

On the other hand, with such a code, the change already appears correctly

var product = await _dbContext.Products
                .Include(x => x.Additionals).SingleOrDefaultAsync(p => p.Id == Id);

product.Name = "ChangedName";
await _dbContext.SaveChangesAsync();   //correct changes

var product = await _dbContext.Products
                .Include(x => x.Additionals).SingleOrDefaultAsync(p => p.Id == Id);

product.Name = "ChangedName";
await _dbContext.SaveChangesAsync();   //correct changes

Can I somehow make changes to the truncated retrieved data like in the first code?

2 Replies

Angius•2y ago

Well, yeah After .Select() it's a different object What if you .Select(p => p.Price)? Or .Select(p => new { Cost = p.Price, Text = p.Name }? EF has no way to track those If you want to edit the entity, you need it whole Or you can use .ExecuteUpdateAsync() that was added in EF Core 7 .Select() is used when you only intend to display the values, not change them

Accord•2y 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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❔ EntityFramework does not track changes for the select projection