Is it possible to commit a read only field using EF to the database in Cosmos?

Question

I would like to store a "calculated field" in a Cosmos document.
For example, I would like to store CostGross to be used in reporting, but EFCore should be responsible for sending the value in inserts/updates:

    public class OrderItem
    {
        public decimal CostNet { get; set; }

        public decimal CostVat { get; set; }

        public decimal CostGross => CostNet + CostVat;
    }

expected document in Cosmos (trimmed for brevity):

{
    ...
    "CostNet": 1,
    "CostVat": 0.2,
    "CostGross": 1.2
    ...
}

actual document in Cosmos (trimmed for brevity):

{
    ...
    "CostNet": 1,
    "CostVat": 0.2
    ...
}

Is it possible to use EF to map a field so that the read only property appears in the document, meaning that the value doesn't have to be re-calculated by other clients doing a read operation?

Thanks

score 0 · Answer 1 · edited Apr 03 '21 at 04:05

0

Yes, you can save data in any object schema. Just populate OrderItem and save it.

edited Apr 03 '21 at 04:05

Nimantha

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answered Feb 22 '21 at 14:15

Harshita Singh

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Hi @singhh-msft Unfortunately it does not. I've updated the question with the result I am getting. – zXynK Feb 23 '21 at 12:24
Can you try adding calculation in set{} once? This essentially just gets the property : https://stackoverflow.com/questions/31764532/what-is-the-assignment-in-c-sharp-in-a-property-signature – Harshita Singh Feb 23 '21 at 13:36
I could have a setter that does nothing. I was hoping to avoid that – zXynK Feb 23 '21 at 13:51
Not empty setter, add CostNet + CostVat in the setter block – Harshita Singh Feb 23 '21 at 15:50
You've lost me there sorry. Could you show me what you mean by amending this fiddle? https://dotnetfiddle.net/0fYubH Thanks – zXynK Feb 23 '21 at 16:02
Check out the fiddle. – Harshita Singh Mar 01 '21 at 07:57
It looks the same. Do you need to fork it and send a new URL? – zXynK Mar 01 '21 at 10:32
Change it to `public decimal CostGross { get {return CostNet + CostVat;} set{} }` – Harshita Singh Mar 01 '21 at 12:01
Hi. That idea will work but as I mentioned, I was hoping to avoid an empty setter – zXynK Mar 01 '21 at 13:30
Ok, try this: `public decimal CostGross { get {return CostNet + CostVat;}}`. – Harshita Singh Mar 01 '21 at 13:51
That's exactly what it's doing now. `public decimal CostGross => CostNet + CostVat;` is the same as your suggestion – zXynK Mar 01 '21 at 15:00
I know, but can you check, sometimes, we miss out on small things. Otherwise, `public decimal CostGross { get {return CostNet + CostVat;} set{} }` should work. – Harshita Singh Mar 01 '21 at 15:19
It does work, but I want to avoid empty setters. It's not good practice – zXynK Mar 01 '21 at 15:42
Did you ever figure out a solution other than the empty setter? – Solo812 Sep 07 '22 at 03:13

score 0 · Answer 2 · answered Apr 03 '21 at 19:14

0

In Ef core 3 this is possible but you need to tweak your model builder

See this GitHub issue https://github.com/dotnet/efcore/issues/18998#issuecomment-557702703

Relevant code

protected override void OnModelCreating(ModelBuilder modelBuilder)
 {
 modelBuilder
     .Entity<User>()
     .Property(e => e.FullName)
     .UsePropertyAccessMode(PropertyAccessMode.Property); //need this line


 }

That should cause EF core 3.0 to store the computed property in the database since Ef would read the property instead of the backing fields directly

answered Apr 03 '21 at 19:14

RubberChickenLeader

983
8
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Hi, Thanks for your reply. Unfortunately this doesn't work without a setter either: `System.InvalidOperationException: 'The property 'OrderItem.CostGross' does not have a setter. Either make the property writable or use a different 'PropertyAccessMode'.'` – zXynK Apr 06 '21 at 08:44
@zXynK If you want to hack around, my next thought would be to add a setter that does nothing, just an empty set – RubberChickenLeader Apr 06 '21 at 13:31
that's my approach at the moment but I was hoping to avoid that – zXynK Apr 07 '21 at 08:13

Is it possible to commit a read only field using EF to the database in Cosmos?

2 Answers2