.NET Framework 4.5.2+
.NET Framework 4.5.2+
.NET Standard 2.0+

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.v20.2.dll

Declaration

public Task<object> ExecuteScalarAsync(
    string sql,
    object[] parameterValues,
    CancellationToken cancellationToken = default(CancellationToken)
)
Public Function ExecuteScalarAsync(
    sql As String,
    parameterValues As Object(),
    cancellationToken As CancellationToken = Nothing
) As Task(Of Object)

Parameters

Name Type Description
sql String

Specifies an SQL statement.

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>

A Task<TResult> that returns the first column of the first row in the query's result set. A null reference (Nothing in Visual Basic) if the result set does not contain columns. DBNull.Value if the first column does not contain a value.

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.

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;
}

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.

See Also