DA20 - Data Abstract Adapters

 

DA20 - Data Abstract Adapters

本文说明什么是 Data Abstract Adapters , 如何运行 , 以及 XML Adapter 可用于与 .Net, Java 或其他支持 XML 操作的语言生成的系统交换数据的 新特性 .

Data Adapters

Data Adapters 是一个 Data Abstract 架构中的支持数据特定格式化并在网络传输和本地存储的组件 . 此外 , data adapters 也可以同样处理数据表的 Delta 信息 .

Data Abstract 提供了两个 Data Adapter:

• TDABINAdapter: 将数据集数据转换为适当的二进制格式.这个Adapter是最快的一个也是在不需要考虑与外部系统互用时的首选.
• TDAXMLAdapter: 将数据集数据转换为XML文档. 这个XML格式是Data Abstract特有的,但是这个组件应用XSLT 轻松转化为其他格式

虽然你可以使用 data adapter 做其他任务 ( 例如使用 XML Adapter 将数据集数据转化为 HTML 页面 ), 但是它们通常用于客户端的 Data Tables 以及服务端的远程服务 ( 见 ServiceAdapter 属性 ). Data Tables 和 DARemoteServices 需要 data adapters 指定如何序列化或反序列化数据 .

所有的 data adapters 继承于 TDADataAdapter (uDADataTable.pas 单元 ).

TDADataAdapter 提供了所有写入或读取 Adapter 的必要方法 . 下面的代码展示了如何使用 XML Data Adapter 序列化两个查询 (Schema 中预先定义的 Customers 和 Orders ) 的数据 :

var

  conn : IDAConnection;

 orders, customers : IDADataset;

 xmlstream : TMemoryStream;

begin

xmlstream := TMemoryStream.Create;

try

  // Opens a database connections and queries for the two tables

  conn := ConnectionManager.NewConnection( 'ADO' );

 customers := Schema.NewDataset(conn, ds_Customers);

 orders := Schema.NewDataset(conn, ds_Orders);

  // Writes the data into the stream by using the XML Adapter

  XMLAdapter.WriteXSLT := NIL; // In case there's one set

  XMLAdapter.Initialize(xmlstream, aiWrite);

  XMLAdapter.WriteDataset(customers, [woSchema, woRows]);

 XMLAdapter.WriteDataset(orders, [woSchema, woRows]);

 XMLAdapter.Finalize;

 [..]

执行这段代码后 , xmlstream 流中将包含如下格式的 XML 文档 :

< XMLData >< Schema >< Datasets >< Customers >< Fields >

< Field Alignment =" taLeftJustify " BlobType =" dabtUnknown "

  BusinessRulesID ="" Calculated =" False " CustomAttributes =" 10370684 "

  DataType =" datAutoInc " DefaultValue ="" Description =""

  DictionaryEntry ="" DisplayFormat ="" DisplayLabel =" CustomerIdx "

  DisplayWidth =" 0 " EditFormat ="" EditMask ="" GeneratorName =""

  InPrimaryKey =" True " KeyFields ="" LogChanges =" True " Lookup =" False "

  LookupCache =" False " LookupKeyFields ="" LookupResultField =""

  LookupSource =" 0 " Name =" CustomerIdx " ReadOnly =" False "

  RegExpression ="" Required =" True " ServerAutoRefresh =" False " Size =" 0 "

  Visible =" True "/>

< Field Alignment =" taLeftJustify " BlobType =" dabtUnknown "

  BusinessRulesID ="" Calculated =" False " CustomAttributes =" 10370916 "

  DataType =" datString " DefaultValue ="" Description =""

  DictionaryEntry ="" DisplayFormat ="" DisplayLabel =" FirstName "

  DisplayWidth =" 0 " EditFormat ="" EditMask ="" GeneratorName =""

  InPrimaryKey =" False " KeyFields ="" LogChanges =" True " Lookup =" False "

  LookupCache =" False " LookupKeyFields ="" LookupResultField =""

  LookupSource =" 0 " Name =" FirstName " ReadOnly =" False " RegExpression =""

  Required =" True " ServerAutoRefresh =" False " Size =" 20 " Visible =" True "/>

[..]

</ Fields ></ Customers >

< Orders >< Fields >

[..]

< Field Alignment =" taLeftJustify " BlobType =" dabtUnknown "

  BusinessRulesID ="" Calculated =" False " CustomAttributes =" 10407460 "

  DataType =" datDateTime " DefaultValue ="" Description =""

  DictionaryEntry ="" DisplayFormat ="" DisplayLabel =" InsertDate "

  DisplayWidth =" 0 " EditFormat ="" EditMask ="" GeneratorName =""

  InPrimaryKey =" False " KeyFields ="" LogChanges =" True " Lookup =" False "

  LookupCache =" False " LookupKeyFields ="" LookupResultField =""

  LookupSource =" 0 " Name =" InsertDate " ReadOnly =" False " RegExpression =""

  Required =" True " ServerAutoRefresh =" False " Size =" 0 " Visible =" True "/>

< Field Alignment =" taLeftJustify " BlobType =" dabtUnknown "

  BusinessRulesID ="" Calculated =" False " CustomAttributes =" 10407692 "

  DataType =" datDateTime " DefaultValue ="" Description =""

  DictionaryEntry ="" DisplayFormat ="" DisplayLabel =" ShipDate "

  DisplayWidth =" 0 " EditFormat ="" EditMask ="" GeneratorName =""

  InPrimaryKey =" False " KeyFields ="" LogChanges =" True " Lookup =" False "

  LookupCache =" False " LookupKeyFields ="" LookupResultField =""

  LookupSource =" 0 " Name =" ShipDate " ReadOnly =" False " RegExpression =""

  Required =" False " ServerAutoRefresh =" False " Size =" 0 " Visible =" True "/>

[..]

</ Fields ></ Orders ></ Datasets ></ Schema >

< Datasets >< Customers >

< Row CustomerIdx =" 1 " FirstName =" Wilton " LastName =" Forster "

  Address1 =" 1371 Inventing Street " City =" Jefferson " State =" SC "

  Zip =" 72680 " Phone1 =" (701) 618-2856 " Email =" [email protected] "/>

< Row CustomerIdx =" 2 " FirstName =" Doyle " MiddleName =" Barry "

  LastName =" Acherman " Address1 =" 3322 Widened Street " City =" Mcallen "

  State =" TX " Zip =" 64448 " Phone1 =" (653) 818-8635 " Fax =" (364) 702-7820 "

  Email =" [email protected] "/>

< Row CustomerIdx =" 3 " FirstName =" Fanchon " LastName =" Kuehler "

  Address1 =" 6767 Sleepily Street " City =" Killeen " State =" MT " Zip =" 18460 "

  Phone1 =" (742) 613-6096 " Phone2 =" (459) 475-9756 "

  Email =" [email protected] "/>

[..]

</ Customers >

< Orders >

[..]

< Row OrderIdx =" 14466 " CustomerIdx =" 6 " ShipperIdx =" 3 "

  TotalPrice =" 47555.93 " ShippingCost =" 66.98 " InsertedBy =" 10 "

  InsertDate =" 11/5/2003 11:20:27 AM " ShipDate =" 11/8/2003 11:20:27 AM "/>

< Row OrderIdx =" 14559 " CustomerIdx =" 3 " ShipperIdx =" 4 "

  TotalPrice =" 39819.58 " ShippingCost =" 40.51 " InsertedBy =" 10 "

  InsertDate =" 9/17/2003 5:10:17 AM " ShipDate =" 9/21/2003 5:10:17 AM "/>

< Row OrderIdx =" 14566 " CustomerIdx =" 4 " ShipperIdx =" 5 "

  TotalPrice =" 94003 " ShippingCost =" 67.94 " InsertedBy =" 5 "

  InsertDate =" 3/3/2004 5:05:27 PM " ShipDate =" 3/8/2004 5:05:27 PM "/>

< Row OrderIdx =" 14725 " CustomerIdx =" 9 " ShipperIdx =" 3 "

  TotalPrice =" 36270.27 " ShippingCost =" 60.77 " InsertedBy =" 7 "

  InsertDate =" 7/22/2003 6:51:48 PM " ShipDate =" 7/25/2003 6:51:48 PM "/>

</ Orders ></ Datasets ></ XMLData >

这里只显示其中部分条目的信息 , 完全的文件 (DatasetSample.xml) 请见本文上面的代码连接 .

如果你要从这个 XML 文件的内容中重新获取这两个数据集 , 代码如下 :

// Loads the data in the data tables

  XMLAdapter.Initialize(xmlstream, aiRead);

 XMLAdapter.ReadDataset(ds_Orders, dtOrders, TRUE);

 XMLAdapter.ReadDataset(ds_Customers, dtCustomers, TRUE);

 XMLAdapter.Finalize;

如果你需要保存这两个数据表的变更 Delta, 你必须使用 WriteDelta 和 ReadDelta 方法 . 例如 :

var xmlstream : TMemoryStream;

 [..]

begin

  [..]

 xmlstream := TMemoryStream.Create;

 try

    // Generates some test updates (ask confirmation first)

    CreateTestUpdates;

    // Erases the XSLT in case there's one set

    XMLAdapter.WriteXSLT := NIL; // In case there's one set

    // Writes the data table deltas into the stream

    // by using the XML Adapter

    XMLAdapter.Initialize(xmlstream, aiWrite);

    XMLAdapter.WriteDelta(dtCustomers);

    XMLAdapter.WriteDelta(dtOrders);

    XMLAdapter.Finalize;

这段代码执行后 ,xmlstream 中将包含如下格式的 XML 文档 :

< XMLData >< Schema >< Deltas >< Customers >< LoggedFields >

 < Field Name =" CustomerIdx " DataType =" datAutoInc "/>

 < Field Name =" FirstName " DataType =" datString "/>

 < Field Name =" MiddleName " DataType =" datString "/>

[..]

</ LoggedFields >

< KeyFields >< Field Name =" CustomerIdx "/></ KeyFields ></ Customers >

< Orders >< LoggedFields >

 < Field Name =" OrderIdx " DataType =" datAutoInc "/>

 < Field Name =" CustomerIdx " DataType =" datInteger "/>

[..]

</ LoggedFields >

< KeyFields >< Field Name =" OrderIdx "/></ KeyFields >

</ Orders ></ Deltas ></ Schema >

< Deltas >

< Customers >

< Row >< RecID > 10 </ RecID >< ChangeType > ctDelete </ ChangeType >

 < Status > csPending </ Status >< Message ></ Message >< OldValues

  CustomerIdx =" 10 " FirstName =" Hester " MiddleName ="" LastName =" Rivera "

  Address1 =" 11275 Prematurity Lane " Address2 ="" City =" Turner " State =" IL "

  Zip =" 40587 " Phone1 =" (717) 345-9144 " Phone2 ="" Fax =""

  Email =" [email protected] " CreditCard =" 6482554456718807 "/>

 < NewValues CustomerIdx ="" FirstName ="" MiddleName ="" LastName =""

  Address1 ="" Address2 ="" City ="" State ="" Zip ="" Phone1 ="" Phone2 =""

  Fax ="" Email ="" CreditCard =""/></ Row >

< Row >< RecID > 11 </ RecID >< ChangeType > ctInsert </ ChangeType >

 < Status > csPending </ Status >< Message ></ Message >< OldValues

  CustomerIdx ="" FirstName ="" MiddleName ="" LastName ="" Address1 =""

  Address2 ="" City ="" State ="" Zip ="" Phone1 ="" Phone2 ="" Fax =""

  Email ="" CreditCard =""/>< NewValues CustomerIdx =" -1 " FirstName =" John "

  MiddleName ="" LastName =" Smith " Address1 =" 202 North Lake Drive "

  Address2 ="" City =" Barrington " State =" IL " Zip =" 60010 "

  Phone1 =" 847 389 2112 " Phone2 ="" Fax ="" Email =" [email protected] "

  CreditCard =" 3333-2222-1111-2 "/></ Row >

[..]

</ Customers >

< Orders >

< Row >< RecID > 113 </ RecID >< ChangeType > ctDelete </ ChangeType >

 < Status > csPending </ Status >< Message ></ Message >< OldValues

  OrderIdx =" 12078 " CustomerIdx =" 8 " ShipperIdx =" 3 "

  TotalPrice =" 30925.13 " ShippingCost =" 64.07 " InsertedBy =" 9 "

  InsertDate =" 7/17/2003 9:34:56 AM " ShipDate =" 7/20/2003 9:34:56 AM "/>

 < NewValues OrderIdx ="" CustomerIdx ="" ShipperIdx ="" TotalPrice =""

  ShippingCost ="" InsertedBy ="" InsertDate ="" ShipDate =""/></ Row >

< Row >< RecID > 114 </ RecID >< ChangeType > ctDelete </ ChangeType >

 < Status > csPending </ Status >< Message ></ Message >

 < OldValues OrderIdx =" 12552 " CustomerIdx =" 8 " ShipperIdx =" 4 "

  TotalPrice =" 78890.59 " ShippingCost =" 50.37 " InsertedBy =" 7 "

  InsertDate =" 11/5/2003 6:45:39 AM " ShipDate =" 11/9/2003 6:45:39 AM "/>

 < NewValues OrderIdx ="" CustomerIdx ="" ShipperIdx ="" TotalPrice =""

  ShippingCost ="" InsertedBy ="" InsertDate ="" ShipDate =""/></ Row >

[..]

</ Orders ></ Deltas ></ XMLData >

如上面的 , 完全文件 (DeltaSample.xml) 可见本文上面的源码连接 .

为了从这个 XML 文档中重新生成两个初始的 Delta, 必须写如下代码 :

var

  xmlstream : TMemoryStream;

 customersdelta,

 ordersdelta : IDADelta;

begin

  [..]

  // Reads the deltas from the stream

  customersdelta := NewDelta(ds_Customers);

 ordersdelta := NewDelta(ds_Orders);

 xmlstream.Position := 0 ;

 XMLAdapter.Initialize(xmlstream, aiRead);

 XMLAdapter.ReadDelta( 'Customers' , customersdelta);

 XMLAdapter.ReadDelta( 'Orders' , ordersdelta);

 XMLAdapter.Finalize;

可见 Data Abstract data adapter 可以向流中写入多个数据集或 Delta 以便于在客户端与服务端交换数据时节省网络请求 . 上面这些代码可以看作与 XML adapter 是独立的 : binary adapter 也使用同样的代码处理 .

提示 : 唯一不同的地方就是当你直接使用 XML adapter 的特有属性如 Write/ReadXSLT.
如果你希望保持代码的兼容性 , 可以按下面的方式写代码 :

if (MyAdapter is TDAXMLAdapter)

 then TDAXMLAdapter(MyAdapter).WriteXSLT.LoadFromFile := 'c:/test.xsl' ;

XML 格式和 XSLT 转化

XML Data Adapter 的格式非常简单 , 其结构如下 :

< XMLData >

 < Schema >

    < Datasets >

      (this section contains the fields definitions of each dataset

       contained in the document)

    </ Datasets >

    < Deltas >

      (this section contains the definitions of each delta contained

       in the document: the list of the logged fields, their types

       and the key fields)

    </ Deltas >

 </ Schema >

 < Datasets >

    (this section contains the actual data of the datasets)

  </ Datasets >

 < Deltas >

    (this section contains the actual data of the deltas which

     includes information such as change status, message, type, etc.)

  </ Deltas >

</ XMLData >

依赖于我们写入数据流 ( 通过 WriteDataset 或 WriteDelta 方法 ) 的不同内容上面所示的部分可能不包含在最终文档中 . 例如 , 如果我们不写入 Delta, 将不会显示 XMLData/Schema/Deltas 或 XMLData/Deltas. 应该去查看显示的元素而不是假设如何如何 .

这种格式很清晰 , 可用于与已经使用其它格式的系统交换数据 . 例如 , 可能会要求返回 RosettaNet 标准的 XML 格式的数据 (http://www.rosettanet.org/).

XML Adapter 允许你使用 XSLT 脚本与其它格式相互转化 .

如果你对 XSLT 标准不熟悉 , 请看 :

http://www.codeguru.com/Csharp/Csharp/cs_data/xml/article.php/c7801/ (XSLT 指南 , Geoffrey Slinker)

http://maple.cc.kcl.ac.uk/XSLT/ (XSLT 指南 , John Bradley)

XSLT 范例带了两个 XSTL 例子将 Customers 数据转换为不同格式的 XML

上面的数据包含在 CustomersToSimpleXML.xsl ( 见本文上面的代码连接 ).

Customer 数据转换为 HTML 页面 :

也在代码连接中查看 CustomersToHTML.xsl XSLT 文件 .