EF Core Enumeration class throwing exception - ef-core-2.1

Question

I am using an enumeration class like this:
public class BillTransactionState
{
public static readonly BillTransactionState Initialized = new BillTransactionState(1, "Initialized");
public static readonly BillTransactionState Invoiceable = new BillTransactionState(2, "Invoiceable");
public static readonly BillTransactionState NoSow = new BillTransactionState(3, "NoSow");
public static readonly BillTransactionState Invoiced = new BillTransactionState(4, "Invoiced");
public virtual int Id { get; set; }
public virtual string Name { get; set; }
}
I have another class that references BillTransactionState:
public class BillTransactionStateHistory : IEntity<long>
{
public long Id { get; set; }
public DateTime EffectiveDate { get; set; }
public BillTransactionState BillTransactionState { get; set; }
}
In my webapi, when I do something like this:
var billTransactionStateHistory = new BillTransactionStateHistory ({
BillTransaction = BillTransaction .Initialized,
EffectiveDate = DateTime.Now
});
_dbContext.BillTransactionStateHistories.AddAsync(billTransactionStateHistory)
I get an error:
Identity insert is off for BillTransactionState.
I realized EF Core is trying to insert a row in BillTransactionState table with values 1 (for Id) and 'Initliazed'. How can I stop EF Core from trying to insert a row in this enumerated class. Any help regarding this will be highly appreciated. Thank you.

Answer 1

Write your BillTransactionStateHistory model class as follows:
public class BillTransactionStateHistory : IEntity<long>
{
public long Id { get; set; }
public DateTime EffectiveDate { get; set; }
public int BillTransactionState { get; set; }
}
Note: After that don't forget to update the database accordingly!
Then in the Web API Method:
var billTransactionStateHistory = new BillTransactionStateHistory ()
{
BillTransactionState = BillTransactionState.Initialized.Id,
EffectiveDate = DateTime.Now
};
_dbContext.BillTransactionStateHistories.AddAsync(billTransactionStateHistory)

Answer 2

You can see this answer on the official EF Core GitHub repository.
Your enumeration class and entity class would remain the same. You would have to introduce a ValueConverter or use PropertyBuilder.HasConverter to provide your mappings to and from BillTransactionState and int.
Lambda example:
// builder is IEntityTypeConfiguration<BillTransactionStateHistory>
builder.Property(e => e.BillTransactionState)
.HasColumnName("state")
.HasConversion(state => state.Id, stateId => SomeLookupMethod(stateId));
public BillTransactionState SomeLookupMethod(int id)
{
// TODO: Lookup transaction state based on id.
}
Please be aware that EF Core 2.x has issues with value converters and lambdas properly mapping to query expressions. EF Core 3.x has fixed this (related issue)