Session.ExecuteScalarAsync(String, Object[], CancellationToken) Method

Executes the specified SQL query and returns the first column of the first row in the result set returned by the query.

Namespace: DevExpress.Xpo

Assembly: DevExpress.Xpo.v19.2.dll

Declaration

C#

public Task<object> ExecuteScalarAsync(
    string sql,
    object[] parameterValues,
    CancellationToken cancellationToken = default(CancellationToken)
)

VB.NET

Public Function ExecuteScalarAsync(
    sql As String,
    parameterValues As Object(),
    cancellationToken As CancellationToken = Nothing
) As Task(Of Object)

Parameters

Name	Type	Description
sql	String	A String value that specifies a parameterized SQL query.
parameterValues	Object[]	An array of objects specifying parameters to pass to the database server along with the query.

Optional Parameters

Name	Type	Default	Description
cancellationToken	CancellationToken	*null*	A CancellationToken object that delivers a cancellation notice to the running operation.

Returns

Type	Description
Task<Object>	The first column of the first row in the query’s result set. If the column is not found in the result set, a null reference (Nothing in Visual Basic) is returned. If the value in the database is null, DBNull.Value is returned.

Remarks

Use ExecuteScalarAsync to query data stores for a single or aggregate value, without having to retrieve a result set.

The following example demonstrates how to use this method. Here, session is the Session instance.

C#

using System.Threading;
using System.Threading.Tasks;
using DevExpress.Xpo;
using DevExpress.Xpo.DB;
// ...
CancellationTokenSource cts = new CancellationTokenSource();
int ordersCount = await GetEmployeeOrdersCountAsync(cts.Token, 152);
// ...
public async Task<int> GetEmployeeOrdersCountAsync(CancellationToken cancellationToken, 
int employeeId) {
    const string queryString = 
        "SELECT COUNT(*) FROM [Northwind].[dbo].[Orders] WHERE [EmployeeID] = @p1";
    object result = await session.ExecuteScalarAsync(
        queryString, 
        new object[] { employeeId },
        cancellationToken
    );
    return (int)result;
}

VB.NET

Imports System.Threading
Imports System.Threading.Tasks
Imports DevExpress.Xpo
Imports DevExpress.Xpo.DB
' ...
Private cts As New CancellationTokenSource()
Private ordersCount As Integer = Await GetEmployeeOrdersCountAsync(cts.Token, 152)
' ...
Public Async Function GetEmployeeOrdersCountAsync(ByVal cancellationToken As CancellationToken, _
ByVal employeeId As Integer) As Task(Of Integer)
    Const queryString As String = _
        "SELECT COUNT(*) FROM [Northwind].[dbo].[Orders] WHERE [EmployeeID] = @p1"
    Dim result As Object = Await session.ExecuteScalarAsync( _
        queryString, _
        New Object() { employeeId }, _
        cancellationToken)
    Return CType(result, Integer)
End Function

Note that a format of parameter names in a SQL statement depends on the ADO.NET provider and database you use.

To learn more about executing SQL queries in XPO, refer to Direct SQL Queries.

Note

The ExecuteScalarAsync method sends queries directly, so the correct query syntax depends on a particular database server.