Developing Database Applications with the Microsoft .NET Framework

Cary JensenJensen Data Systems, Inc.

Data Access in Delphi 2005 for .NET

BDE.NET dbExpress.NET dbGO (ADO for .NET) MyBase.NET IBExpress.NET DataSet Client for .NET ADO.NET BDP.NET

VCL.NET vs ADO.NET

BDE.NETdbExpress.NETdbGo (ADO for .NET)ClientDataSetsIBX.NETDataSnap .NET ClientThird-Party VCL for .NET Datasets

ADO.NETBDP.NETThird-Party .NET Data Providers

VCL.NET ADO.NET

BDE Advantages

If you already have it installed and working for existing applications, new applications require little or no configuration to use it.

Many legacy applications exist which use it. Two or more applications written in Delphi can easily

share global aliases. It has relatively good performance across a large

number of data types It provides access to installed ODBC drivers Available for Windows and .NET

BDE Limitations

In the typically deployment of BDE-based applications, a copy of the BDE must be installed and configured on each workstation (a network installation is possible, but requires manual registry configuration)

The BDE is somewhat inefficient, in that it stores as many as three copies of table metadata

When used with local tables such as Paradox tables, failure to correctly configure the BDE can produce periodic index corruption

If a new BDE application is incorrectly installed, existing BDE applications may fail to initialize properly

Not available for Linux Borland SQL Links for Windows have been deprecated

dbExpress Advantages

Data-related operations in dbExpress tend to be faster than the BDE

dbExpress-based applications can be deployed on Win32, .NET, and Linux platforms

Applications designed to use dbExpress can more easily be ported to using DataSnap

dbExpress applications require fewer support files and can require far less configuration than BDE applications

dbExpress Limitations

dbExpress applications are generally more complicated than other types of Delphi database applications to program. In addition to requiring more components to access and edit data, dbExpress applications generally require more lines of code than non-dbExpress applications

No equivalent to midaslib, dbexpint units. Must deploy midas.dll, dbexpint.dll, dbxintf.dll, etc.

There are few dbExpress drivers currently available. Information about deploying dbExpress application

compiled using Delphi 8 is scarce

MyBase.NET Advantages

ClientDataSet applications have minimal installation requirements

The data can be stored in XML format, making it easy to access this data from outside of the application

Data can be loaded and saved without code. Simply point the ClientDataSet's FileName property to a file that contains the proper XML or binary client dataset data, and it will take care of the rest. (It is better to explicity load and save using SaveToFile and LoadFromFile.)

Available in Windows, .NET, and Linux

MyBase Limitations

Because the records in a client dataset are stored in-memory, the number of records that you can load is limited by the amount of real and virtual memory available on your machine

Large files may take a significant amount of time to load from a file into a client dataset

ClientDataSet applications are limited to single user applications. If you want to create a multiuser application, you must use one of the other available technologies

Requires the deployment of additional DLLs (midas.dll, …)

dbGo (ADO for .NET) Advantages

Any Windows-based computer shipped in the past few years already has MDAC installed. As a result, most ADO-based applications require only the installation of the specific OLE DB provider, at most.

ADO can be used from a wide range of development environments, including MS Access, VisualBasic, Delphi, Visual C++, to name of few.

A wide range of OLE DB providers are available.

dbGo (ADO for .NET) Limitations

While MDAC is available on many machines, it is not available on all (for example, Windows 95 machines do not have MDAC installed by default). These machines must have MDAC (and DCOM) installed before an ADO-enabled application can run

ADO is available only for the 32-bit Windows operating system Having MDAC installed and configured is not enough. In some cases, you

must also install and register an appropriate OLE DB provider Performance using ADO is largely reliant on the quality of the OLE DB provider

that you are using Applies to VCL.NET only If you are using the OLE DB provider for ODBC, an appropriate ODBC driver

must also be installed and configured

InterBase Express Advantages

InterBase Express provides access to InterBase without the BDE

Because InterBase Express components are designed specifically for InterBase, they include a number of specialized components that access and leverage InterBase features

Interbase Express components are available for Windows, .NET, and Linux

InterBase Express Limitations

InterBase Express works only with the InterBase database server

DataSnap Advantages

DataSnap client applications have few installation requirements

Business rules can be implemented on a server, permitting these rules to be updated independent of the individual client applications

They provide a reliable, distributed upgrade path to dbExpress and MyBase applications

DataSnap Limitations

While DataSnap offers additional flexibility over traditional client/server solutions, it requires more development. Specifically, in addition to writing the client application, you also need to write the application server.

Cannot write DataSnap servers in Delphi 8 Delphi 8 only supports DCOM connections Delphi 8 does not support load balancing or fail-over DataSnap applications require an additional license before they can be

deployed. This license can be found in the Enterprise edition of Delphi. DataSnap servers must also employ one of the other data access

mechanisms As with other ClientDataSet examples, you must deploy midas.dll.

Advantages of Third-Party Data Access Mechanisms

They likely provide optimized access to a particular file type or database server.

They may support the familiar TDataSet interface.They are likely to provide support for proprietary database features.As is the case with the Advantage TDataSet Descendant for Delphi

8, they may provide cross-platform support

Limitations Third-Party Data Access Mechanisms

They likely support only one vendor's databaseYou must rely on the producer of the third-party data access

mechanism to stay current with Borland technologies

Advantages of ADO.NET

Supported by all first-class .NET languagesNative to the FCLResults in smaller executablesWorks with third-party .NET data providersPowerful in-memory DataSetsTight integration with XML

Limitations of ADO.NET

Only for the .NET platformCompared with TDataSet.NET solutions, sports a different interface

from previous Delphi implementationsWhen using with third-party .NET data providers, requires the

deployment of additional assembliesDifferent type namespaces for different .NET data providers

Advantages of BDP.NET

Portable code : Write once and connect to all supported DB’sOpen Architecture: Lets you add support to more DB’s easilyLogical Data types mapped to .NET Native types Consistent data type mapping across DB’sUnlike OLEDB .NET Provider, no need to go through a COM interop

layer. Support for Database specific featuresLive, Delphi-like design-time data viewsValuable component editors

Limitations of BDP.NET

Yet another proprietary data access mechanismRequires the installation of additional assemblies into the global

assembly cacheThere are few BDP.NET supported databasesUses the ADO.NET interfaces as opposed to the TDataSet interfacesCurrent design-time code generation is aggressive, providing more

features than you may wantNot supported on Win32 or Linux platforms

Database

ADO.NET Major Interfaces and Classes

IDbConnection

IDataReader

IDbDataAdapter

IDbCommand

IDbParameter

DataSet

DataTableCollection

DataRelationCollection

DataTable

DataRow

DataRowCollection

DataColumnCollection

DataColumn

DataRelation

DataView

Constraint

DataRowView

XML Document

DataSets, DataTables, and DataRows

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DataSet

var Table: DataTable; Row: DataRow; data: String;begin Table := DataSet1.Tables[0]; Row := Table.Rows[2]; data := Row[1].ToString();

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Table1

Table2

DataSets, DataTables, and DataRows

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DataSet

var data: String;begin data := DataSet1.Tables[0].Rows[2][1].ToString()

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Table1

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Controls and CurrencyManagers

All controls, that is, classes that descend from Control in the .NET FCL, are data aware, and can be bound to a data source. A BindingManagerBase instance is created anytime a control is bound to a new data source.

Controls that are bound to the same data source are bound to the same BindingManagerBase instance. BindingManagerBase is an abstract class, and two concrete classes descend from it. These concrete classes are CurrencyManager and PropertyManager.

Creating a Data Module

Create a form that will serve as the data module (let’s call this form the data module) Add the ADO.NET components that you want to share to the public section of the data module's class declaration.

When the data module is created, create the instances of, and configure, the ADO.NET classes that you added to the form's public section

Add one Control descendant to the data module for each data source that you want to use in other forms. Bind each control to the data source you want to expose.

Declare a variable of the data module class type within scope of each form that must use a data module data source

For each form that uses the data module, assign that form’s BindingContext property to the data module's (form-level) BindingContext property.

For each Control descendant on each form, set the binding context (or DataSource and DataMember properties) to the appropriate data source on the data module.

Field References in Expressions

Use the ColumnName property to reference fields if ColumnName contains one of the following characters,

the field reference must be enclosed in brackets: (space), \n (newline), \t (tab), \r (carriage return), ~, (, ), #, \, /, =, >, <, +, -, *, %, &, |, ^, ‘, “, [,]

For consistency, you can use brackets even when the column name does not include one of the special characters.

If your column name includes the ] character, it must be preceded by a \.

Field Reference Examples

Column NameAccountNoAccount#Last NameColumn[1]

ReferenceAccountNo[Account#][Last Name][Column[1\]]

Literals

Strings enclosed in single quotesex: 'Mr ' + [Contact Name]

Dates enclosed between # characters:ex: [Date] - #1/1/2004#

Numeric values, including decimal values and scientific notation, are not delimitedex: [Percent] * 100

String Literals and Delphi

Consider the following string assignment (in C#):

dataColumn1.Expression = "'Mr ' + [First Name] + ' ' + [Last Name] ";

String literals are more complicated for Delphi developers, since single quotes are

already used to delimit strings. For example: DataColumn1.Expression := '''Mr ''' + ' + [First Name] + ' + ''' ''' + ' + [Last Name]';

You can also use the QuotedStr function in Borland.Vcl.SysUtils:DataColumn1.Expression := QuotedStr('Mr ') + ' + [First Name] + ' + QuotedStr(' ') + ' + [Last Name]';

Alternatively, enclose string literals between #39, like this:DataColumn2.Expression := #39 + 'Mr ' + #39 + ' + [Invoice No] + ' + #39 + ' ' + #39 + ' + [Customer ID]';

You can even omit the concatenation operator (+) between #39 and strings:DataColumn2.Expression := #39'Mr '#39' + [Invoice No] + '#39' '#39' + [Customer ID]';

Comparison operators (in order of precedence)

<

>

<=

>=

<>

=

IN

LIKE

Boolean Operators

( expression) AND OR NOT

Programmatically Create Calculated Fields

Create a DataColumn in your DataTable that will hold the calculated field

After loading data, iterate through the DataTable and assign the calculation. Then make the calculated field to readonly

Add a ColumnChanged event handler to the DataTable From the ColumnChanged event handler, test whether the

changed field is one of those involved in the calculation. If so, make the calculated field writeable, re-calculate the calculation, then make the field readonly once again

DataSync and DataHub

New components introduced in Delphi 2005 Provide a richer mechanism for data handling Works with both ADO.NET data providers and BDP

for .NET data providers Permit live views of data at design time Provide a migration path for remote data access

DataSync and DataHub

RemoteServer and RemoteConnection

Provide automatic .NET remoting for .NET datasets Add a RemoteServer to an application Connect the RemoteServer to that application’s

DataSync Add a RemoteConnection to a client application Connect the RemoteConnection to a DataHub to provide

it with access to the DataSync on the server

RemoteServer and RemoteConnection

Thank You !

Thank You !