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Showing content from https://docs.microsoft.com/en-us/dotnet/api/system.data.linq.mapping.columnattribute.expression below:

ColumnAttribute.Expression Property (System.Data.Linq.Mapping) | Microsoft Learn

ColumnAttribute.Expression Property Definition

Gets or sets whether a column is a computed column in a database.

public:
 property System::String ^ Expression { System::String ^ get(); void set(System::String ^ value); };

public string Expression { get; set; }

member this.Expression : string with get, set

Public Property Expression As String

Property Value

Default = empty.

Examples

[Column(Storage="_UnitPrice", DbType="Money",Expression="UnitPrice + 1.00")]
public System.Nullable<decimal> UnitPrice
{
    get
    {
        return this._UnitPrice;
    }
    set
    {
        if ((this._UnitPrice != value))
        {
            this.OnUnitPriceChanging(value);
            this.SendPropertyChanging();
            this._UnitPrice = value;
            this.SendPropertyChanged("UnitPrice");
            this.OnUnitPriceChanged();
        }
    }
}

   <Column(Storage:="_UnitPrice", DbType:="Money NOT NULL", Expression:="UnitPrice + 1.00")> _
Public Property UnitPrice() As Decimal
       Get
           Return Me._UnitPrice
       End Get
       Set(ByVal value As Decimal)
           If ((Me._UnitPrice = Value) _
              = False) Then
               Me.OnUnitPriceChanging(Value)
               Me.SendPropertyChanging()
               Me._UnitPrice = Value
               Me.SendPropertyChanged("UnitPrice")
               Me.OnUnitPriceChanged()
           End If
       End Set
   End Property

Remarks

Use this property when you use CreateDatabase to define a column as containing computed values.

For example, if you want to create a column defined in SQL as InventoryVal AS UnitPrice * UnitsInStock, use the following expression string: "UnitPrice * UnitsInStock".

Note

LINQ to SQL does not support computed columns as primary keys.

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