WEB三层结构的设计思路

青旅半醒 2022-08-11 00:48 187阅读 0赞

WEB三层结构的设计思路

1.DAL层的设计：

1.1.强类型的DataTable并不包括如何访问对应底层的数据表的任何信息,DataTable的作用是在分层间传输数据。要获取用来填充DataTable的

数据 ，我们使用TableAdapter类，它提供了数据访问层的功能,对于TableAdapter类中的自定义方法,我们使用部分类来保存。

using System;

using System.Data;

using NorthwindTableAdapters;

public partial class Northwind

public partial class SuppliersRow

public Northwind.ProductsDataTable GetProducts()

ProductsTableAdapter productsAdapter = new ProductsTableAdapter();

return productsAdapter.GetProductsBySupplierID(this.SupplierID);

1.2.如果使用DB直接模式,DataSet设计器会根据SELECT语句自动生成插入，更新，删除方法,而且不会受SELECT子句中的子查询的影响。但如果

使用JOIN语句的话，DataSet设计器就不能自动生成插入，更新，以及删除数据库记录的方法了,这时,必须手工设置InsertCommand，

UpdateCommand和DeleteCommand属性值.

SELECT ProductID, ProductName, SupplierID, CategoryID,

QuantityPerUnit, UnitPrice, UnitsInStock, UnitsOnOrder, ReorderLevel, Discontinued,

(SELECT CategoryName FROM Categories

WHERE Categories.CategoryID = Products.CategoryID) as CategoryName,

(SELECT CompanyName FROM Suppliers

WHERE Suppliers.SupplierID = Products.SupplierID) as SupplierName

FROM Products

2.BLL层的设计:

2.1简单的调用DAL中的方法

using System;

using System.Data;

using System.Configuration;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

using NorthwindTableAdapters;

\[System.ComponentModel.DataObject\]

public class ProductsBLL

private ProductsTableAdapter \_productsAdapter = null;

protected ProductsTableAdapter Adapter

get \{

if (\_productsAdapter == null)

\_productsAdapter = new ProductsTableAdapter();

return \_productsAdapter;

\[System.ComponentModel.DataObjectMethodAttribute(System.ComponentModel.DataObjectMethodType.Select, true)\]

public Northwind.ProductsDataTable GetProducts()

return Adapter.GetProducts();

\[System.ComponentModel.DataObjectMethodAttribute(System.ComponentModel.DataObjectMethodType.Select, false)\]

public Northwind.ProductsDataTable GetProductByProductID(int productID)

return Adapter.GetProductByProductID(productID);

\[System.ComponentModel.DataObjectMethodAttribute(System.ComponentModel.DataObjectMethodType.Select, false)\]

public Northwind.ProductsDataTable GetProductsByCategoryID(int categoryID)

return Adapter.GetProductsByCategoryID(categoryID);

\[System.ComponentModel.DataObjectMethodAttribute(System.ComponentModel.DataObjectMethodType.Select, false)\]

public Northwind.ProductsDataTable GetProductsBySupplierID(int supplierID)

return Adapter.GetProductsBySupplierID(supplierID);

\[System.ComponentModel.DataObjectMethodAttribute(System.ComponentModel.DataObjectMethodType.Insert, true)\]

public bool AddProduct(string productName, int? supplierID, int? categoryID, string quantityPerUnit,

decimal? unitPrice, short? unitsInStock, short? unitsOnOrder, short? reorderLevel,

bool discontinued)

// 新建一个ProductRow实例

Northwind.ProductsDataTable products = new Northwind.ProductsDataTable();

Northwind.ProductsRow product = products.NewProductsRow();

product.ProductName = productName;

if (supplierID == null) product.SetSupplierIDNull(); else product.SupplierID = supplierID.Value;

if (categoryID == null) product.SetCategoryIDNull(); else product.CategoryID = categoryID.Value;

if (quantityPerUnit == null) product.SetQuantityPerUnitNull(); else product.QuantityPerUnit = quantityPerUnit;

if (unitPrice == null) product.SetUnitPriceNull(); else product.UnitPrice = unitPrice.Value;

if (unitsInStock == null) product.SetUnitsInStockNull(); else product.UnitsInStock = unitsInStock.Value;

if (unitsOnOrder == null) product.SetUnitsOnOrderNull(); else product.UnitsOnOrder = unitsOnOrder.Value;

if (reorderLevel == null) product.SetReorderLevelNull(); else product.ReorderLevel = reorderLevel.Value;

product.Discontinued = discontinued;

// 添加新产品

products.AddProductsRow(product);

int rowsAffected = Adapter.Update(products);

// 如果刚好新增了一条记录，则返回true，否则返回false

return rowsAffected == 1;

\[System.ComponentModel.DataObjectMethodAttribute(System.ComponentModel.DataObjectMethodType.Update, true)\]

public bool UpdateProduct(string productName, int? supplierID, int? categoryID, string quantityPerUnit,

decimal? unitPrice, short? unitsInStock, short? unitsOnOrder, short? reorderLevel,

bool discontinued, int productID)

Northwind.ProductsDataTable products = Adapter.GetProductByProductID(productID);

if (products.Count == 0)

// 没有找到匹配的记录，返回false

return false;

Northwind.ProductsRow product = products\[0\];

product.ProductName = productName;

if (supplierID == null) product.SetSupplierIDNull(); else product.SupplierID = supplierID.Value;

if (categoryID == null) product.SetCategoryIDNull(); else product.CategoryID = categoryID.Value;

if (quantityPerUnit == null) product.SetQuantityPerUnitNull(); else product.QuantityPerUnit = quantityPerUnit;

if (unitPrice == null) product.SetUnitPriceNull(); else product.UnitPrice = unitPrice.Value;

if (unitsInStock == null) product.SetUnitsInStockNull(); else product.UnitsInStock = unitsInStock.Value;

if (unitsOnOrder == null) product.SetUnitsOnOrderNull(); else product.UnitsOnOrder = unitsOnOrder.Value;

if (reorderLevel == null) product.SetReorderLevelNull(); else product.ReorderLevel = reorderLevel.Value;

product.Discontinued = discontinued;

// 更新产品记录

int rowsAffected = Adapter.Update(product);

// 如果刚好更新了一条记录，则返回true，否则返回false

return rowsAffected == 1;

\[System.ComponentModel.DataObjectMethodAttribute(System.ComponentModel.DataObjectMethodType.Delete, true)\]

public bool DeleteProduct(int productID)

int rowsAffected = Adapter.Delete(productID);

// 如果刚好删除了一条记录，则返回true，否则返回false

return rowsAffected == 1;

2.2.给DataRow添加字段级验证

新建一个名为ProductsDataTable.ColumnChanging.cs的类文件

public partial class Northwind

public partial class ProductsDataTable

public override void BeginInit()

this.ColumnChanging += ValidateColumn;

void ValidateColumn(object sender, DataColumnChangeEventArgs e)

if(e.Column.Equals(this.UnitPriceColumn))

if(!Convert.IsDBNull(e.ProposedValue) && (decimal)e.ProposedValue < 0)

throw new ArgumentException("UnitPrice cannot be less than zero", "UnitPrice");

else if (e.Column.Equals(this.UnitsInStockColumn) ||

e.Column.Equals(this.UnitsOnOrderColumn) ||

e.Column.Equals(this.ReorderLevelColumn))

if (!Convert.IsDBNull(e.ProposedValue) && (short)e.ProposedValue < 0)

throw new ArgumentException(string.Format("\{0\} cannot be less than zero", e.Column.ColumnName),

e.Column.ColumnName);

2.3添加业务规则

public bool UpdateProduct(string productName, int? supplierID, int? categoryID, string quantityPerUnit,

decimal? unitPrice, short? unitsInStock, short? unitsOnOrder, short? reorderLevel,

bool discontinued, int productID)

Northwind.ProductsDataTable products = Adapter.GetProductByProductID(productID);

if (products.Count == 0)

// 没有找到匹配项，返回false

return false;

Northwind.ProductsRow product = products\[0\];

// 业务规则检查 – 不能停用某供应商所提供的唯一一个产品

if (discontinued)

// 获取我们从这个供应商处获得的所有产品

Northwind.ProductsDataTable productsBySupplier = Adapter.GetProductsBySupplierID(product.SupplierID);

if (productsBySupplier.Count == 1)

// 这是我们从这个供应商处获得的唯一一个产品

throw new ApplicationException("You cannot mark a product as discontinued if its the only product purchased

from a supplier");

product.ProductName = productName;

if (supplierID == null) product.SetSupplierIDNull(); else product.SupplierID = supplierID.Value;

if (categoryID == null) product.SetCategoryIDNull(); else product.CategoryID = categoryID.Value;

if (quantityPerUnit == null) product.SetQuantityPerUnitNull(); else product.QuantityPerUnit = quantityPerUnit;

if (unitPrice == null) product.SetUnitPriceNull(); else product.UnitPrice = unitPrice.Value;

if (unitsInStock == null) product.SetUnitsInStockNull(); else product.UnitsInStock = unitsInStock.Value;

if (unitsOnOrder == null) product.SetUnitsOnOrderNull(); else product.UnitsOnOrder = unitsOnOrder.Value;

if (reorderLevel == null) product.SetReorderLevelNull(); else product.ReorderLevel = reorderLevel.Value;

product.Discontinued = discontinued;

// 更新产品记录

int rowsAffected = Adapter.Update(product);

// 如果刚好更新了一条记录，则返回true，否则返回false

return rowsAffected == 1;

2.4在表示层中对异常的处理

那么表示层如何捕捉到异常？一种是通过try...catch()的方法，另一种就是通过WEB控件中的事件来捕捉异常。  
在插入、更新或删除操作的过程中，数据Web控件和ObjectDataSource控件都包含了pre- 和post-级的事件，它们记录着当前的操作。当使用一  
个可编辑的GridView时，事件触发顺序如下：ObjectDataSource\_Updating-->GridView\_RowUpdating-->GridView\_RowUpdated--  
>ObjectDataSource\_Updated  
我们可以为这些发生在操作之前的事件创建事件处理程序，目的是自定义输入参数；为发生在操作之后的事件创建事件处理，目的是检测和相应操作的结果。Post-level的事件处理程序通常用作侦测在操作过程中是否出现了一个异常。当面对一个异常时，这些post-level的事件处理程序可以随意地处理该异常。

示例1：

ProductsBLL productLogic = new ProductsBLL();  
// 更新ProductID为1的产品信息  
try  
\{  
// 这个操作将会失败，因为我们试图使用一个小于0的UnitPrice  
productLogic.UpdateProduct("Scott's Tea", 1, 1, null, -14m, 10, null, null, false, 1);  
\}  
catch (ArgumentException ae)  
\{  
Response.Write("There was a problem: " + ae.Message);  
\}

示例2：  
protected void GridView1\_RowUpdated(object sender, GridViewUpdatedEventArgs e)  
\{  
if (e.Exception != null)  
\{  
// Display a user-friendly message  
ExceptionDetails.Visible = true;  
ExceptionDetails.Text = "There was a problem updating the product. ";  
if (e.Exception.InnerException != null)  
\{  
Exception inner = e.Exception.InnerException;  
if (inner is System.Data.Common.DbException)  
ExceptionDetails.Text += "Our database is currently experiencing problems. Please try again later.";  
else if (inner is NoNullAllowedException)  
ExceptionDetails.Text += "There are one or more required fields that are missing.";  
else if (inner is ArgumentException)  
\{  
string paramName = ((ArgumentException)inner).ParamName;  
ExceptionDetails.Text += string.Concat("The ", paramName, " value is illegal.");  
\}  
else if (inner is ApplicationException)ExceptionDetails.Text += inner.Message;  
\}  
// Indicate that the exception has been handled  
e.ExceptionHandled = true;  
// Keep the row in edit mode  
e.KeepInEditMode = true;  
\}  
\}

总之，每个工单由3部分组成(DAL,BLL,Web)，DAL和BLL都有相应有命名空间.  
如工单MPR:则可以建一个NetSoft.MPR.DAL和NetSoft.MPR.BLL,然后再做一个WEB模板。这样就可以实现三层结构，而且可以使代码量较少。