Generate an unique string for a field in a pre-defined pattern when save using Code First Approch: Entity Framework

Question

I have a table called Quotations and it has an unique string field called QuotationNo.

public class Quotation
{
    [Key]
    public int Id { get; set; } //PK
    public string QuotationNo{ get; set; } // Pattern QUOT/12-22/00001 => QUOT + MONTH-YEAR + PrimaryKey.ToStrin("5d");
}

So I have implemented it by calling _db.SaveChanges() method twice as follows.

if (ModelState.IsValid)
{
     _db.Quotations.Add(quot);
     _db.SaveChanges(); // 1 time saving
    
     quot.QuotationNo= "QUOT/" + DateTime.Today.ToString("dd-MM/") + quot.Id.ToString("D5");
     _db.Quotations.Update(quot);
     _db.SaveChanges(); // 2 time saving
}

Is there a short way to do this?

Answer 1

I found this method is more clear.

Step 1: Creating new field in the table to store DateCreated.

Step 2: Making QuotationNo a virtual and NotMapped field, which is always a calculated/generated field.

See the code

public class Quotation
{
    [Key]
    public int Id { get; set; } //PK
    [Required]
    public DateTime DateCreated { get; set; } //New field to store quotation created date.
    [NotMapped]
    public virtual string? QuotationNo  //Ax Key(Quotation No: QUOT/01-22/0000001=> PQTN/mmYY/0000000)
    {
         get
         {
             return $"QUOT/{this.DateCreated:dd-MM/}{PolyCostingId:D5}"; 
         }
         set
         {
             this.PolyCostingCode = value;
         }
    }
}