NotMapped atribute .NET 5.0

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NotMapped atribute .NET 5.0

Andrej Čačala 6

I´m trying to use data anotation NOTMAPPED in .NET 5 and when i run aplication i get error that collumn can not find in db. In NET framework what i used before on this project was working fine

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Answer 1

Michael Wang-MSFT 1,066

Hi, @Andrej Čačala ,

The NotMapped attribute is still supported in .NET 5. It can be applied to properties of an entity class for which we do not want to create corresponding columns in the database. By default, EF creates a column for each property (must have get; & set;) in an entity class. The [NotMapped] attribute overrides this default convention. You can apply the [NotMapped] attribute on one or more properties for which you do NOT want to create a corresponding column in a database table.

public class Student  
    {  
        public int Id { get; set; }  
        public string Name { get; set; }  
  
        [NotMapped]  
        public int Age { get; set; }  
    }

The above model maps to the database as shown below.

Alternatively you could try Ignore() :

protected override void OnModelCreating(DbModelBuilder modelBuilder)  
{  
   modelBuilder.Entity<Student>().Ignore(m => m.Age );  
   base.OnModelCreating(modelBuilder);  
}

If the answer doesn’t solve your issue, please provide more details of error that will help us track down what’s happening.

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Best Regards,
Michael Wang

Yurii Zhukow 1 Reputation point

2022-01-07T09:48:22.447+00:00

The problem is that when marking a propery with [NotMapped] attribute, this property still involved in EF model. No need to explain how it should work. Better explain why it doesn`t work.
AgaveJoe 31,361 Reputation points

2022-01-07T14:45:11.617+00:00

I tested the [NotMapped] attribute in .NET Core and [NotMapped] does not create a table column as expected. Is there anyway you can provide example code and the steps to reproduce this behavior?

Yurii Zhukow 1

Seems, this happens when [NotMapped] property is declared on base abstract class, while EF table is based on derived class. At least in my case.

[Serializable]
    public abstract class BaseClass {

        [NotMapped, JsonIgnore]
        public string Label { get; set; } // Here we declare hidden prop

}

public class MiddleClass : BaseClass {} // derived



public class MyEntityClass : MiddleClass { 

// our EF entity

}

AgaveJoe 31,361 Reputation points

2022-01-07T22:06:09.737+00:00

While I do not agree with the design approach, I still cannot reproduce this issue with two layer of inheritance. My best guess is you are trying to use the property in a LINQ query which of course is not possible since the column does not exist in the table.

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NotMapped atribute .NET 5.0

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