IdentityAttribute Class

.NET Standard 2.x

Specifies that the database generates a value for the property when a row is inserted.

Namespace: SnapObjects.Data

Assembly: SnapObjects.Data.dll

Inheritance Constructor

System.Attribute

Syntax

  public class IdentityAttribute : Attribute

Examples

The following code example demonstrates how to use the Identity attribute. In the Person class, the PersonID property is applied with the Identity attribute. When a Person object is created, the PersonID property needs not to be assigned with a value, instead the database will automatically assign a value to it.

Model: Person

using System;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using SnapObjects.Data;

namespace Appeon.ApiDoc.Models.School
{
    /// <summary>
    /// This model class maps to the dbo.Person table. 
    /// When Discriminator is 'Instructor', it represents an instructor record; 
    /// when Discriminator is 'Student', it represents a student record.
    /// 
    /// It uses the primary key to generate the Where clause for the Update operation.
    /// 
    /// PersonID is the pimary key and the identity.
    /// </summary>
    [Table("Person", Schema = "dbo")]
    [UpdateWhereStrategy(UpdateWhereStrategy.KeyColumns)]
    public class Person
    {
        [Key]
        [Identity]
        public int PersonID { get; set; }

        public string LastName { get; set; }

        public string FirstName { get; set; }

        public DateTime? HireDate { get; set; }

        public DateTime? EnrollmentDate { get; set; }

        public string Discriminator { get; set; }

    }
}

Example Method:

using Appeon.ApiDoc.Models.School;

namespace Appeon.ApiDoc.IdentityAttributeExamples
{
    public class IdentityAttributeExample
    {
        private SchoolContext _context;

        public IdentityAttributeExample(SchoolContext dataContext)
        {
            // Sets the data context.
            _context = dataContext;
        }

        public void Example()
        {
            var mapper = _context.SqlModelMapper;

            // Adds a Person record.
            var person = new Person()
            {
                LastName = "Walker",
                FirstName = "Kim",
                Discriminator = "Student"
            };

            mapper.TrackCreate(person).SaveChanges();

            /* The following INSERT SQL is generated: 
            exec sp_executesql N'INSERT 
            INTO [dbo].[Person] ([LastName], [FirstName], [Discriminator])
            VALUES (@p0, @p1, @p2);
            SELECT [PersonID]
            FROM [dbo].[Person]
            WHERE @@ROWCOUNT = 1 AND [PersonID] = scope_identity();

            ',N'@p0 nvarchar(4000),@p1 nvarchar(4000),@p2 nvarchar(4000)',
            @p0=N'Walker',@p1=N'Kim',@p2=N'Student'         
            */
        }
    }
}