要解决Asp.net core 2.2 webapi中SQL依赖更改事件处理程序仅触发一次而不是多次的问题,你可以使用一个静态变量来跟踪事件是否已经触发过。
以下是一个代码示例:
services.AddDbContext(options =>
options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
// 注册SQL依赖更改事件处理程序
services.AddSingleton();
public interface ISqlDependencyService
{
void Configure(string connectionString, string tableName);
}
public class SqlDependencyService : ISqlDependencyService
{
private static bool _isDependencySet;
public void Configure(string connectionString, string tableName)
{
if (!_isDependencySet)
{
// 设置SQL依赖
using (SqlConnection connection = new SqlConnection(connectionString))
{
using (SqlCommand command = new SqlCommand($"SELECT * FROM {tableName}", connection))
{
// 为SQL命令启用查询通知
SqlDependency.Start(connectionString);
SqlDependency dependency = new SqlDependency(command);
dependency.OnChange += Dependency_OnChange;
// 执行SQL命令
connection.Open();
command.ExecuteReader();
}
}
_isDependencySet = true;
}
}
private void Dependency_OnChange(object sender, SqlNotificationEventArgs e)
{
// 处理SQL依赖更改事件
if (e.Type == SqlNotificationType.Change)
{
// 在这里编写处理逻辑
Console.WriteLine("SQL dependency changed");
}
// 重新设置SQL依赖
Configure(ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString, "YourTableName");
}
}
public class MyController : ControllerBase
{
private readonly ISqlDependencyService _sqlDependencyService;
public MyController(ISqlDependencyService sqlDependencyService)
{
_sqlDependencyService = sqlDependencyService;
}
[HttpGet("configure-dependency")]
public IActionResult ConfigureDependency()
{
_sqlDependencyService.Configure(Configuration.GetConnectionString("DefaultConnection"), "YourTableName");
return Ok();
}
}
这样,当你调用ConfigureDependency API时,将会设置SQL依赖并在更改事件发生时触发一次处理程序。