Entity Framework to read a column but prevent it being updated

Question

Given a database table with a column that contains historic data but that is no longer populated, is there a way in Entity Framework to read the column but prevent it being updated when using the same model object?

For example I have an object

public class MyObject
{
    public string CurrentDataColumnName { get; set; }
    public string HistoricDataColumnName { get; set; }
}

From the documentation I don’t believe I can do either of the following, because this will stop EF reading the data as well as persisting it.

(1) Decorate the HistoricDataColumnName property with the following attribute

[NotMapped]

(2) Add the following to my EntityTypeConfiguration for MyObject

Ignore(x => x.HistoricDataColumnName)

Answer 1

You can mark the column as computed to prevent Entity Framework from updating / inserting into that column.

[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
public string HistoricDataColumnName { get; set; }

---

DatabaseGenerated

An important database features is the ability to have computed properties. If you're mapping your Code First classes to tables that contain computed columns, you don't want Entity Framework to try to update those columns. But you do want EF to return those values from the database after you've inserted or updated data. You can use the DatabaseGenerated annotation to flag those properties in your class along with the Computed enum. Other enums are None and Identity.

Answer 2

You can simply use IsModified to check whether a specific entity property was modified or not and by this way you can still Read,Insert and Delete data:

var item = context.MyObjects.Find(id);
item.CurrentDataColumnName = "ChangedCurrentDataColumnName";
item.HistoricDataColumnName = "ChangedHistoricDataColumnName";
context.Entry(item).Property(c => c.HistoricDataColumnName).IsModified = false;
context.SaveChanges();

By using IsModified = false you are excluding the HistoricDataColumnName property from updating, so the HistoricDataColumnName column will not be updated in the database but other properties will be updated.

Setting this value to false for a modified property will revert the change by setting the current value to the original value. If the result is that no properties of the entity are marked as modified, then the entity will be marked as Unchanged. Setting this value to false for properties of Added, Unchanged, or Deleted entities is a no-op.

Check the following answer as a supplementary explanation. It might be helpful also:

https://stackoverflow.com/a/13503683/2946329