EF Core - How to create a relation when the foreign key is a concatenated field with constant value

Question

I have to map in Entity Framework a database with weird relations. There is no primary key nor foreign key, I guess relations by analysing already existing SQl request. And there is a case I cannot define in fluent api.

The SQL request

SELECT *
FROM TABLE_A A
INNER JOIN TABLE_B B ON A.Company = B.Company AND A.Kind = 7 AND A.[Key] = CONCAT(B.Field1, B.Field2, '000', B.Field3) 

I expect a one to one relationship, so I tried somethink like that in the context:

modelBuilder.Entity<Table_A>(A =>
    A.HasOne(x => x.Table_B).WithOne(x => x.Table_A)
   .HasForeignKey<Table_B>(x => new { x.Company, x.Kind, x.Key })
   .HasPrincipalKey<Table_A>(x => new { Company = x.Company, Kind = 7, Key = $"{x.Field1}{x.Field2}000{x.Field3}" });
);

I got an error that told I must use direct property acces in the HasPrincipalKey object construction.

I also tried to create a read only property in the Table_A class like that:

Public virtual string Key => $"{Field1}{Field2}000{Field3}";

and I adapt the context (I remove the Kind property because of the constant)

modelBuilder.Entity<Table_A>(A =>
        A.HasOne(x => x.Table_B).WithOne(x => x.Table_A)
       .HasForeignKey<Table_B>(x => new { x.Company x.Key })
       .HasPrincipalKey<Table_A>(x => new { x.Company, x.Key });
    );

in that case I have a message about a missing setter on the property Key. I also tried various stuff but without any success.

If anyone knows how to translate this SQL relation into EF Core fluent API, I would be glad to hear it. Thank you