在Linq中使用.NET 4动态关键字的好例子?

这里有一个想法:通过将LINQ与dynamic结合起来,您可以查询非类型化的数据集,就像它们是类型化的一样。

例如,假设myDataSet是一个非类型化的数据集。使用动态类型和名为AsDynamic()的扩展方法,可以执行以下操作:

var query = from cust in myDataSet.Tables[0].AsDynamic()
  where cust.LastName.StartsWith ("A")
  orderby cust.LastName, cust.FirstName
  select new { cust.ID, cust.LastName, cust.FirstName, cust.BirthDate };

下面是如何定义AsDynamic扩展方法。注意它如何返回IEnumerable of dynamic,这使它适合于LINQ查询:

public static class Extensions
{    
  public static IEnumerable<dynamic> AsDynamic (this DataTable dt)
  {
    foreach (DataRow row in dt.Rows) yield return row.AsDynamic();
  }

  public static dynamic AsDynamic (this DataRow row)
  {
    return new DynamicDataRow (row);
  }

  class DynamicDataRow : DynamicObject
  {
    DataRow _row;
    public DynamicDataRow (DataRow row) { _row = row; }

    public override bool TryGetMember (GetMemberBinder binder, out object result)
    {
      result = _row[binder.Name];
      return true;
    }

    public override bool TrySetMember (SetMemberBinder binder, object value)
    {
      _row[binder.Name] = value;
      return true;
    }

    public override IEnumerable<string> GetDynamicMemberNames()
    {   
        return _row.Table.Columns.Cast<DataColumn>().Select (dc => dc.ColumnName);
    }
  }
}

乔的回答很酷。我知道如何简化用法。如果将此添加到扩展类中:

public static class Extensions
{    

    public static IEnumerable<dynamic> ExecuteSql(this UserQuery uq, string sql)
    {
        var connStr="Provider=SQLOLEDB.1;"+uq.Connection.ConnectionString; 

        OleDbConnection connection = new OleDbConnection(connStr);
        DataSet myDataSet = new DataSet();
        connection.Open();

        OleDbDataAdapter DBAdapter = new OleDbDataAdapter();
        DBAdapter.SelectCommand = new OleDbCommand(sql, connection); 
        DBAdapter.Fill(myDataSet);

        var result = myDataSet.Tables[0].AsDynamic();
        return result;
    }
}

它允许在 LINQPad :

void Main()
{
    var query1 = from cust in this.ExecuteSql("SELECT * from Customers")
        where cust.ContactName.StartsWith ("C")
        orderby cust.ContactName
        select new { cust.CustomerID, cust.ContactName, cust.City };        
    query1.Dump();      
}

N、 B.:

• 添加 System.Data.OleDb 从 System.Data 程序集到查询属性

• 添加 System.Dynamic

• uq.Connection 只有通过“连接”下拉列表关联了数据库时才可用。如果您选择了 "<none>" ,将发生编译错误。

更新: ExecuteQueryDynamic 在 latest Beta v4.53.03 of LinqPad ,可用于实现此目的,例如:

void Main()
{
    var q=this.ExecuteQueryDynamic("select * from Customers");
    q.Dump();
}

这将返回 Customers 来自Northwind数据库的表 IEnumerable<dynamic> ,使用Linq2Sql连接。

 using (SqlConnection connection = new SqlConnection(this.Connection.ConnectionString))
{
  connection.Open();

  SqlCommand command = new SqlCommand(query, connection);
  SqlDataReader reader = command.ExecuteReader();

  reader.Cast<IDataRecord>().AsQueryable().Dump();      
}