ISqlExecutor.ScalarAsync<TValue>(ISqlQueryBuilder sqlQueryBuilder, object[] parameters, CancellationToken cancellationToken) Method

.NET Standard 2.x

Asynchronously executes the SQL SELECT statement created by an ISqlQueryBuilder object and returns the first column of the first row in the result set. All other columns and rows are ignored.

Namespace: SnapObjects.Data

Assembly: SnapObjects.Data.dll

Syntax

public Task<TValue> ScalarAsync<TValue>(ISqlQueryBuilder sqlQueryBuilder, object[] parameters, CancellationToken cancellationToken)

Type Parameters

TValue

The datatype of the first column in the result set.

Parameters

sqlQueryBuilder SnapObjects.Data.ISqlQueryBuilder

A SqlQueryBuilder object which can be used to generate a SQL SELECT statement.

parameters System.Object[]

One or more objects which contain the values corresponding to the SQL parameter identifier names.

You can also pass the arguments directly in the order in which they appear in the SQL SELECT statement generated by sqlQueryBuilder without using the objects.

cancellationToken CancellationToken

A cancellation token that can be used by other objects or threads to receive notice of cancellation.

Returns

Task<TValue>

Returns a task that represents the asynchronous operation.

Remarks

You can use parameter placeholders in the raw SQL Statement. It is recommended to use the syntax for parameter placeholders that is specific to the data source. e.g., uses @parametername for SQL Server and uses :parametername for Oracle.

Examples

The following code example demonstrates how to use the ScalarAsync<TValue> (ISqlQueryBuilder, params object[], CancellationTokenSource) method to execute the SQL statement generated by an ISqlQueryBuilder object. It uses a CancellationTokenSource type parameter to make this operation cancelable.

using System;
using System.Threading;
using System.Threading.Tasks;
using SnapObjects.Data;

namespace Appeon.ApiDoc.ISqlExecutorExamples
{
    public class ScalarAsyncExample
    {
        private readonly SchoolContext _context;
        
        public ScalarAsyncExample(SchoolContext dataContext)
        {
            // Sets the data context.
            _context = dataContext;
        }

        public async Task<string> Example4(CancellationTokenSource cts)
        {
            // Creates a SqlQueryBuilder.
            var builder = new SqlQueryBuilder();
            
            var idParam = SqlBuilder.Parameter<int>("id");
            
            // Builds the SQL SELECT statement.
            builder.Select("Title")
                .From("Course")
                .Where("Credits", idParam);
            
            int id = 2;
            string title = null;
                
            try
            {
                // If a task has been cancelled, the call to the 
                // SqlExecutor.ScalarAsync method throws an OperationCanceledException.
                title = await _context.SqlExecutor.ScalarAsync<string>(builder,
                    new object[] { id }, cts.Token);
                    
                Console.WriteLine("Title: {0}", title);
            }
            catch (OperationCanceledException e)
            {
                // The operation was cancelled before completion.
                Console.WriteLine(e.Message);
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
            finally 
            {
                cts.Dispose();
            }
            
            return title;
            
            
            /*This code produces the following output:
            
                A task was canceled.
            */
        }
    }
}

Applies to

.NET Standard

2.x