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?

Store the date created and use a computed column in the database. — Gert Arnold, Dec 22 '22 at 12:44
That's easier. Thanks!! I will create a virtual property with the getter having that logic. — Lakshitha Kanchana, Dec 22 '22 at 14:35

Lakshitha Kanchana · Accepted Answer · 2022-12-24T13:46:43.237

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;
         }
    }
}

score 0 · Answer 2 · edited Dec 24 '22 at 23:55

0

Please try this

public class Quotation
{
    public int Id { get; set; } //PK
    public string QuotationNo
            {
                get
                {
                    return string.IsNullOrWhiteSpace(this.QuotationNo)
                       ? $"QUOT/{DateTime.Today:dd-MM:hh:mm:ss/}{Id:D7}"
                       : this.QuotationNo;
                }

                set { this.QuotationNo = value; }
            }}

For example

var x = new Quotation();
x.Id = 12345;
var quotationNo = x.QuotationNo; 
// quotationNo will be QUOT/22-12/0012345

Some reference here Setting the default value of a DateTime Property to DateTime.Now inside the System.ComponentModel Default Value Attrbute

edited Dec 24 '22 at 23:55

Lakshitha Kanchana

844
2
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answered Dec 22 '22 at 06:51

MichaelMao

2,596
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dd-MM are not saved in the database here? I think setter should be changed. – Lakshitha Kanchana Dec 22 '22 at 07:08
1

Please check the updated answer I add a example for you. ```DateTime.Today:dd-MM/``` is shortcut for ```DateTime.Today.ToString("dd-MM/")``` – MichaelMao Dec 22 '22 at 07:13
If the same quotation was viewed next month. The quotation number will be different. It is not what I expected. – Lakshitha Kanchana Dec 22 '22 at 07:14
I think you're right. Just thinking how to do it – MichaelMao Dec 22 '22 at 07:36
@LakshithaKanchana Could you try my updated answer, I add second to test it – MichaelMao Dec 22 '22 at 07:49
Sorry, took long to discover, there is an issue with {Id:D7} section. Because Id is the primary key auto increment type, it is generated by the DB itself. So {Id:D7} always be 0000000? – Lakshitha Kanchana Dec 24 '22 at 13:44

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

2 Answers2