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Mikhail
Asked:2020-10-22 19:54:01 +0000 UTC2020-10-22 19:54:01 +0000 UTC

将计算列添加到强类型数据集中的表中

  • 772

我在强类型 ShopDB 数据集中有 2 个表。Orders 表通过外键 FK_Employees_Orders 通过 EmployeeID 字段连接到Employees 表：

在此处输入图像描述

我的任务是显示每个员工的总销售额。（做类似 LEFT JOIN 的事情，但我想以不同的方式解决问题）。这是我的代码：

ShopDB shopDB = new ShopDB();
var employeesTableAdapter = new ShopDBTableAdapters.EmployeesTableAdapter();
employeesTableAdapter.Fill(shopDB.Employees);

var ordersTableAdapter = new ShopDBTableAdapters.OrdersTableAdapter();
ordersTableAdapter.Fill(shopDB.Orders);

ShopDB.EmployeesDataTable employees = employeesTableAdapter.GetData();
ShopDB.OrdersDataTable orders = ordersTableAdapter.GetData();
employees.Columns.Add("AggregateColumn", typeof(double), "Count(Child(FK_Orders_Employees).EmployeeID)"); /*название отношения взял из определения ShopDB.Designer.cs*/

 foreach (DataRow employeeRow in employees.Rows)
        {
            foreach (DataColumn employeeColumn in employees.Columns)
                Console.WriteLine("{0}: {1}", employeeColumn.ColumnName, employeeRow[employeeColumn]);

调试时，在添加列的那一行出现异常：错误

System.Data.EvaluateException HResult=0x80131920 消息 = 复合表达式“System.Data.AggregateNode”中的未绑定引用。Source = System.Data 堆栈跟踪：在 System.Data.AggregateNode.Eval（DataRow 行，DataRowVersion 版本）在 System.Data.DataExpression.Evaluate（DataRow 行，DataRowVersion 版本）在 System.Data.DataTable.EvaluateExpressions（DataColumn 列）到 System.Data.DataColumn.set_Expression(String value) 到 System.Data.DataColumnCollection.AddAt(Int32 index, DataColumn column) 到 System.Data.DataColumnCollection.Add(String columnName, Type type, String expression)

你能建议什么可能是解决方案吗？

c#

1 个回答

  1. Best Answer

    我得到了我想要的。我放弃了这段关系，使用了 Linq，一切都解决了：

            ShopDB shopDB = new ShopDB();

        var employeesTableAdapter = new ShopDBTableAdapters.EmployeesTableAdapter();
        employeesTableAdapter.Fill(shopDB.Employees);

        var ordersTableAdapter = new ShopDBTableAdapters.OrdersTableAdapter();
        ordersTableAdapter.Fill(shopDB.Orders);

        var orderDetailsTableAdapter = new ShopDBTableAdapters.OrderDetailsTableAdapter();
        orderDetailsTableAdapter.Fill(shopDB.OrderDetails);

        ShopDB.EmployeesDataTable employees = employeesTableAdapter.GetData();
        ShopDB.OrdersDataTable orders = ordersTableAdapter.GetData();

        employees.Columns.Add("Count", typeof(int));
        foreach (DataRow employeeRow in employees.Rows)
        {
            employeeRow["Count"] = orders.Count(o => o.EmployeeID == (int)employeeRow["EmployeeID"]);

            foreach (DataColumn column in employees.Columns) {
                if (column.ColumnName=="EmployeeID" || column.ColumnName == "Count")
                    Console.WriteLine("{0}: {1}", column.ColumnName, employeeRow[column]);
            }
            Console.WriteLine();
        }

    }

    在此处输入图像描述

    • 2

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