5.14 异步方法_MySQL 连接器/NET 开发人员指南

MySQL 连接器/NET 开发人员指南 / 第 5 章连接器/NET 编程 / 5.14 异步方法

5.14 异步方法

基于任务的异步模式 (TAP) 是 .NET Framework 中的一种异步模式。它基于命名空间中的 Task和Task<TResult> 类型，System.Threading.Tasks用于表示任意异步操作。

Async-Await是为与 TAP 一起使用而引入的新关键字。Async 修饰符用于指定方法、lambda 表达式或匿名方法是异步的。Await 运算符应用于异步方法中的任务，以暂停方法的执行，直到等待的任务完成。

要求

异步等待支持需要 .NET Framework 4.5 或更高版本
TAP支持需要 .NET Framework 4.0 或更高版本
MySQL 连接器/NET 6.9 或更高版本

方法

以下方法可与 TAP 或 Async-Await 一起使用。

命名空间MySql.Data.Entity
- 班级EFMySqlCommand
  - Task PrepareAsync()
  - Task PrepareAsync(CancellationToken)
命名空间MySql.Data
- 班级MySqlBulkLoader
  - Task<int> LoadAsync()
  - Task<int> LoadAsync(CancellationToken
- 班级MySqlConnection
  - Task<MySqlTransaction> BeginTransactionAsync()
  - Task<MySqlTransaction> BeginTransactionAsync (CancellationToken)
  - Task<MySqlTransaction> BeginTransactionAsync(IsolationLevel)
  - Task<MySqlTransaction> BeginTransactionAsync (IsolationLevel , CancellationToken)
  - Task ChangeDatabaseAsync(string)
  - Task ChangeDatabaseAsync(string, CancellationToken)
  - Task CloseAsync()
  - Task CloseAsync(CancellationToken)
  - Task ClearPoolAsync(MySqlConnection)
  - Task ClearPoolAsync(MySqlConnection, CancellationToken)
  - Task ClearAllPoolsAsync()
  - Task ClearAllPoolsAsync(CancellationToken)
  - Task<MySqlSchemaCollection> GetSchemaCollection(string, string[])
  - Task<MySqlSchemaCollection> GetSchemaCollection(string, string[], CancellationToken)
- 班级MySqlDataAdapter
  - Task<int> FillAsync(DataSet)
  - Task<int> FillAsync(DataSet, CancellationToken)
  - Task<int> FillAsync(DataTable)
  - Task<int> FillAsync(DataTable, CancellationToken)
  - Task<int> FillAsync(DataSet, string)
  - Task<int> FillAsync(DataSet, string, CancellationToken)
  - Task<int> FillAsync(DataTable, IDataReader)
  - Task<int> FillAsync(DataTable, IDataReader, CancellationToken)
  - Task<int> FillAsync(DataTable, IDbCommand, CommandBehavior)
  - Task<int> FillAsync(DataTable, IDbCommand, CommandBehavior, CancellationToken)
  - Task<int> FillAsync(int, int, params DataTable[])
  - Task<int> FillAsync(int, int, params DataTable[], CancellationToken)
  - Task<int> FillAsync(DataSet, int, int, string)
  - Task<int> FillAsync(DataSet, int, int, string, CancellationToken)
  - Task<int> FillAsync(DataSet, string, IDataReader, int, int)
  - Task<int> FillAsync(DataSet, string, IDataReader, int, int, CancellationToken)
  - Task<int> FillAsync(DataTable[], int, int, IDbCommand, CommandBehavior)
  - Task<int> FillAsync(DataTable[], int, int, IDbCommand, CommandBehavior, CancellationToken)
  - Task<int> FillAsync(DataSet, int, int, string, IDbCommand, CommandBehavior)
  - Task<int> FillAsync(DataSet, int, int, string, IDbCommand, CommandBehavior, CancellationToken)
  - Task<DataTable[]> FillSchemaAsync(DataSet, SchemaType)
  - Task<DataTable[]> FillSchemaAsync(DataSet, SchemaType, CancellationToken)
  - Task<DataTable[]> FillSchemaAsync(DataSet, SchemaType, string)
  - Task<DataTable[]> FillSchemaAsync(DataSet, SchemaType, string, CancellationToken)
  - Task<DataTable[]> FillSchemaAsync(DataSet, SchemaType, string, IDataReader)
  - Task<DataTable[]> FillSchemaAsync(DataSet, SchemaType, string, IDataReader, CancellationToken)
  - Task<DataTable[]> FillSchemaAsync(DataSet, SchemaType, IDbCommand, string, CommandBehavior)
  - Task<DataTable[]> FillSchemaAsync(DataSet, SchemaType, IDbCommand, string, CommandBehavior, CancellationToken)
  - Task<DataTable> FillSchemaAsync(DataTable, SchemaType)
  - Task<DataTable> FillSchemaAsync(DataTable, SchemaType, CancellationToken)
  - Task<DataTable> FillSchemaAsync(DataTable, SchemaType, IDataReader)
  - Task<DataTable> FillSchemaAsync(DataTable, SchemaType, IDataReader, CancellationToken)
  - Task<DataTable> FillSchemaAsync(DataTable, SchemaType, IDbCommand, CommandBehavior)
  - Task<DataTable> FillSchemaAsync(DataTable, SchemaType, IDbCommand, CommandBehavior, CancellationToken)
  - Task<int> UpdateAsync(DataRow[])
  - Task<int> UpdateAsync(DataRow[], CancellationToken)
  - Task<int> UpdateAsync(DataSet)
  - Task<int> UpdateAsync(DataSet, CancellationToken)
  - Task<int> UpdateAsync(DataTable)
  - Task<int> UpdateAsync(DataTable, CancellationToken)
  - Task<int> UpdateAsync(DataRow[], DataTableMapping, CancellationToken)
  - Task<int> UpdateAsync(DataSet, string)
  - Task<int> UpdateAsync(DataSet, string, CancellationToken)
- 班级MySqlHelper
  - Task<DataRow> ExecuteDataRowAsync(string, string, params MySqlParameter[])
  - Task<DataRow> ExecuteDataRowAsync(string, string, CancellationToken, params MySqlParameter[])
  - Task<int> ExecuteNonQueryAsync(MySqlConnection, string, params MySqlParameter[])
  - Task<int> ExecuteNonQueryAsync(MySqlConnection, string, CancellationToken, params MySqlParameter[])
  - Task<int> ExecuteNonQueryAsync(string, string, params MySqlParameter[])
  - Task<int> ExecuteNonQueryAsync(string, string, CancellationToken, params MySqlParameter[])
  - Task<DataSet> ExecuteDatasetAsync(string, string)
  - Task<DataSet> ExecuteDatasetAsync(string, string, CancellationToken)
  - Task<DataSet> ExecuteDatasetAsync(string, string, CancellationToken, params MySqlParameter[])
  - Task<DataSet> ExecuteDatasetAsync(MySqlConnection, string)
  - Task<DataSet> ExecuteDatasetAsync(MySqlConnection, string, CancellationToken)
  - Task<DataSet> ExecuteDatasetAsync(MySqlConnection, string, params MySqlParameter[])
  - Task<DataSet> ExecuteDatasetAsync(MySqlConnection, string, CancellationToken, params MySqlParameter[])
  - Task UpdateDataSetAsync(string, string, DataSet, string)
  - Task UpdateDataSetAsync(string, string, DataSet, string, CancellationToken)
  - Task<MySqlDataReader> ExecuteReaderAsync(MySqlConnection, MySqlTransaction, string, MySqlParameter[], bool)
  - Task<MySqlDataReader> ExecuteReaderAsync(MySqlConnection, MySqlTransaction, string, MySqlParameter[], bool, CancellationToken)
  - Task<MySqlDataReader> ExecuteReaderAsync(string, string)
  - Task<MySqlDataReader> ExecuteReaderAsync(string, string, CancellationToken)
  - Task<MySqlDataReader> ExecuteReaderAsync(MySqlConnection, string)
  - Task<MySqlDataReader> ExecuteReaderAsync(MySqlConnection, string, CancellationToken)
  - Task<MySqlDataReader> ExecuteReaderAsync(string, string, params MySqlParameter[])
  - Task<MySqlDataReader> ExecuteReaderAsync(string, string, CancellationToken, params MySqlParameter[])
  - Task<MySqlDataReader> ExecuteReaderAsync(MySqlConnection, string, params MySqlParameter[])
  - Task<MySqlDataReader> ExecuteReaderAsync(MySqlConnection, string, CancellationToken, params MySqlParameter[])
  - Task<object> ExecuteScalarAsync(string, string)
  - Task<object> ExecuteScalarAsync(string, string, CancellationToken)
  - Task<object> ExecuteScalarAsync(string, string, params MySqlParameter[])
  - Task<object> ExecuteScalarAsync(string, string, CancellationToken, params MySqlParameter[])
  - Task<object> ExecuteScalarAsync(MySqlConnection, string)
  - Task<object> ExecuteScalarAsync(MySqlConnection, string, CancellationToken)
  - Task<object> ExecuteScalarAsync(MySqlConnection, string, params MySqlParameter[])
  - Task<object> ExecuteScalarAsync(MySqlConnection, string, CancellationToken, params MySqlParameter[])
- 班级MySqlScript
  - Task<int> ExecuteAsync()
  - Task<int> ExecuteAsync(CancellationToken)

除了上面列出的方法外，以下是从 .NET Framework 继承的方法：

命名空间MySql.Data.Entity
- 班级EFMySqlCommand
  - Task<DbDataReader> ExecuteDbDataReaderAsync(CommandBehaviour, CancellationToken)
  - Task<int> ExecuteNonQueryAsync()
  - Task<int> ExecuteNonQueryAsync(CancellationToken)
  - Task<DbDataReader> ExecuteReaderAsync()
  - Task<DbDataReader> ExecuteReaderAsync(CancellationToken)
  - Task<DbDataReader> ExecuteReaderAsync(CommandBehaviour)
  - Task<DbDataReader> ExecuteReaderAsync(CommandBehaviour, CancellationToken)
  - Task<object> ExecuteScalarAsync()
  - Task<object> ExecuteScalarAsync(CancellationToken)
命名空间MySql.Data
- 班级MySqlCommand
  - Task<DbDataReader> ExecuteDbDataReaderAsync(CommandBehaviour, CancellationToken)
  - Task<int> ExecuteNonQueryAsync()
  - Task<int> ExecuteNonQueryAsync(CancellationToken)
  - Task<DbDataReader> ExecuteReaderAsync()
  - Task<DbDataReader> ExecuteReaderAsync(CancellationToken)
  - Task<DbDataReader> ExecuteReaderAsync(CommandBehaviour)
  - Task<DbDataReader> ExecuteReaderAsync(CommandBehaviour, CancellationToken)
  - Task<object> ExecuteScalarAsync()
  - Task<object> ExecuteScalarAsync(CancellationToken)
- 班级MySqlConnection
  - Task OpenAsync()
  - Task OpenAsync(CancellationToken)
- 班级MySqlDataReader
  - Task<T> GetFieldValueAsync<T>(int)
  - Task<T> GetFieldValueAsync<T>(int, CancellationToken)
  - Task<bool> IsDBNullAsync(int)
  - Task<bool> IsDBNullAsync(int, CancellationToken)
  - Task<bool> NextResultAsync()
  - Task<bool> NextResultAsync(CancellationToken)
  - Task<bool> ReadAsync()
  - Task<bool> ReadAsync(CancellationToken)

例子

以下 C# 代码示例演示了如何使用异步方法：

在此示例中，方法具有async修饰符，因为进行的方法await调用适用于方法LoadAsync。该方法返回一个 Task对象，该对象包含有关等待方法的结果的信息。返回Task就像有一个 void 方法，但async void如果你的方法不是像事件这样的顶级访问方法，你就不应该使用。

public async Task BulkLoadAsync()
{
  MySqlConnection myConn = new MySqlConnection("MyConnectionString");
  MySqlBulkLoader loader = new MySqlBulkLoader(myConn);

  loader.TableName       = "BulkLoadTest";
  loader.FileName        = @"c:\MyPath\MyFile.txt";
  loader.Timeout         = 0;

  var result             = await loader.LoadAsync();
}

在这个例子中，“async void”方法与“await” ExecuteNonQueryAsync方法一起使用，以对应按钮的 onclick 事件。这就是该方法不返回 Task.

private async void myButton_Click()
{
  MySqlConnection myConn = new MySqlConnection("MyConnectionString");
  MySqlCommand proc      = new MySqlCommand("MyAsyncSpTest", myConn);

  proc.CommandType       = CommandType.StoredProcedure;

  int result             = await proc.ExecuteNonQueryAsync();
}