SelectColumnExpression Class

Defines a column in the SELECT statement by the name, alias and source.

Namespace: DevExpress.DataAccess.DataFederation

Assembly: DevExpress.DataAccess.v24.2.dll

Declaration

C#

public class SelectColumnExpression :
    INodeSelectExpression,
    ISelectExpression,
    IAliasedSelectExpression

VB.NET

Public Class SelectColumnExpression
    Implements INodeSelectExpression,
               ISelectExpression,
               IAliasedSelectExpression

Remarks

To specify a field in the federated query’s SELECT statement, create a SelectColumnExpression object and add it to the SelectNode.Expressions collection.

Tip

Instead of adding multiple SelectColumnExpression instances to the collection, you can call the Source.From extension method to build a query with a Fluent API.

Example

This code snippet demonstrates how to create a federated data source that uses a filter with a parameter.

Note

The complete sample project How to Create a Federated Data Source at Runtime is available in the DevExpress Examples repository.

C#

using DevExpress.DataAccess.DataFederation;
// ...
    FederationDataSource federation = new FederationDataSource();

    Source source = new Source("excelSource", CreateExcelDataSource("SalesPerson.xlsx", "Data"));

    var sourceNode = new SourceNode(source, "Orders");

    var query = new SelectNode(sourceNode)
    {
        Alias = "excel",
        Expressions = {
                new SelectColumnExpression(sourceNode, "OrderID"),
                new SelectColumnExpression(sourceNode, "OrderDate"),
                new SelectColumnExpression(sourceNode, "Sales Person"),
                new SelectColumnExpression(sourceNode, "ProductName"),
                new SelectColumnExpression(sourceNode, "Extended Price")
            },
        FilterString = "[Orders.CategoryName] = ?cat",
    };
    federation.Queries.Add(query);
    federation.Fill(new[] { 
        new DevExpress.DataAccess.Sql.QueryParameter("cat", typeof(string), "Seafood") });

VB.NET

Imports DevExpress.DataAccess.DataFederation
' ... 
    Dim federation As New FederationDataSource()

    Dim source As New Source("excelSource", CreateExcelDataSource("SalesPerson.xlsx", "Data"))

    Dim sourceNode = New SourceNode(source, "Orders")

    Dim query = New SelectNode(sourceNode)
    query.Alias = "excel"
    query.Expressions.Add(New SelectColumnExpression(sourceNode, "OrderID"))
    query.Expressions.Add(New SelectColumnExpression(sourceNode, "OrderDate"))
    query.Expressions.Add(New SelectColumnExpression(sourceNode, "Sales Person"))
    query.Expressions.Add(New SelectColumnExpression(sourceNode, "ProductName"))
    query.Expressions.Add(New SelectColumnExpression(sourceNode, "Extended Price"))
    query.FilterString = "[Orders.CategoryName] = ?cat"
    federation.Queries.Add(query)
    federation.Fill( { 
        New DevExpress.DataAccess.Sql.QueryParameter("cat", GetType(String), "Seafood") })

Implements

INodeSelectExpression

IAliasedSelectExpression

ISelectExpression

Inheritance

Object

SelectColumnExpression