Entity Framework DatabaseGenerated Data Annotations

The DatabaseGenerated attribute is added to the properties whose value is automatically computed/updated by the Database. It specifies how the database generates values for the property. There are three possible values:

• Identity: Specifies that the column is an identity column, which is typically used for integer primary keys.
• Computed: Specifies that the database generates the value for the column.
• None: Specifies that the values are not generated by the database.

DatabaseGeneratedOption.None

The DatabaseGeneratedOption.None prevents the database from creating the computed values, and the values must be provided by the user.

public class Book
{
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int BookId { get; set; }
    public int SrNo { get; set; }
    public string Title { get; set; }
}

The BookId property is denoted with DatabaseGeneratedOption.None, so its value must be specified when inserted into the database.

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DatabaseGeneratedOption.Identity

When DatabaseGenerated.Identity is applied to a property, the Entity Framework expects the data to be updated by the database when the row is inserted.

public class Book
{
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int BookId { get; set; }
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int SrNo { get; set; }
    public string Title { get; set; }
}

The SrNo property is denoted with DatabaseGeneratedOption.Identity so its value will be updated by the database, when the row is inserted.

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DatabaseGeneratedOption.Computed

The DatabaseGeneratedOption.Computed is useful when you have computed columns in your database. EF will not update these columns, but it will query and return the values of these fields once the data is inserted or updated.

public class Book
{
    public int BookId { get; set; }
    public int SrNo { get; set; }
    public string Title { get; set; }
    [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public DateTime? CreatedAt { get; set; } = DateTime.Now;
}