C++Builder, 1, Borland C++Builder White Paper: Intro to Data Components

By: Borland Staff

Abstract: Borland C++Builder offers developers unparalleled power and flexibility for application development.

Introduction to the Database Components in Borland C++Builder
Written by Richard Lussier. Revised by Jeff Cottingham

Data Aware Controls

The data aware controls provide the means for an application to display data from a table to the user. They also allow the user to change the data presented or enter new information. These data-aware controls are counterparts to the standard Windows controls. There are labels, edit controls, comboboxes, radiobuttons, and list boxes. In addition, a spreadsheet-like control called TDBGrid is provided. Below is a list of some of the data-aware controls and descriptions of their functionality. Controls which have many properties in common are discussed first. Sections on TDBGrid, and DBLookupCombo follow. Lastly, the DBNavigator components are discussed.

TDBEdit, TDBCombobox, TDBListbox, TDBRadioGroup, TDBCheckBox, TDBImage, TDBMemo

These controls are very self explanatory and represent data-aware equivalents of standard Windows controls. The key properties for all these fields are:

    DataField: This is the actual field in the table or query. A drop-down list of field names is available from which to choose. This property should be set once the DataSource property is set.

    DataSource: The DataSource property links a data-aware control to a TDataSource object. This establishes the tiered relationship between the DataSet object, DataSource object, and Data Control object.

    ReadOnly: As implied, the developer can specify that a particular field is read-only. This gives much greater control than specifying write access for an entire table.

TDBGrid

TDBGrid offers a spreadsheet-like look for presenting data. In many situations, the spreadsheet metaphor is appropriate. Most users are familiar with its look and feel, and for presenting large amounts of data in a small space, it can't be beat. The DBGrid is also useful when designing forms displaying a 'one-to-many' relationship. Often, the detail records can be easily presented in a DBGrid.

A description of the key properties follows:

    DataSource: Like all the data-aware controls the DataSource property links the DBGrid control to the TDataSource object, which is in turn linked to a TTable or TQuery object.

    Options: The Options property allows a developer to fine-tune the look and operation of the DBGrid. For example, the developer can specify if the user will see Grid Lines, Column Title, or a record indicator, among other options.

TDBLookupList and TDBLookupCombo

These two very powerful data-aware controls offer the C++Builder database application developer an easy way to display "lookup" data to the user. Lookups are usually small tables which contains all the valid values a certain field might hold. For example, in a Customer database, a customer's address is usually entered. The State in which the customer can reside can be a 'lookup' to a States table. This will ensure uniform, clean data in the database. The LookupList and LookupCombo allow you to display the full description of the possible lookup values, but store the lookup code. This serves the dual role of ease of use and smaller database tables - it is nice to show the words "California", or "Massachusetts" to support the selection process of users but store "CA" or "MA" in the Customers State field. The difference can be about 15 characters per customer record for this single field!

Along with the normal data-aware control properties of DataField and DataSource, the properties that allow you to perform the special lookup functions are:

    LookupDisplay: This is the field in the lookup table that contains the description of the lookup code. For example, part number 101 may have a description of "Size 10 Widgets". This property allows the developer to display the more intuitive description rather than the code.

    LookupField: This property is the field in the lookup table that contains the lookup code itself.

    LookupSource: This refers to a DataSource control that ties into the lookup table. Remember, to get information from the lookup table, it too will need a TTable (or TQuery) and TDataSource objects established.


The DBNavigator Component

The DBNavigator is an extraordinarily important and powerful component. This component allows the developer to add the now standard look and feel of 'VCR' controls to a form to allow users to move from record to record. In addition to the First, Last, Next, and Prior buttons, the DBNavigator also has options for Edit, Post, Insert, Delete, Cancel and Refresh! It provides the essential functionality every database application needs. Each button is optional and you can mix and match at will. For example, in a read-only form, you wouldn't want any of the editing buttons. In a client/server application, carefully consider allowing the user to access First or Last buttons as these might result in long queries.


Putting it All Together

Now that your familiar with all the components available to you for database access and manipulation, lets take a brief look at how these components can be put together to create a database form.

Three Steps to Design a Form

Designing a C++Builder database form requires just three simple steps. First, place a DataSet object (TTable or TQuery) on the form and set its properties according to your preferences. Second, put a TDataSource on the form and set its DataSet property to reference the TTable or TQuery object from the first step. Third and last, drop your data-aware controls on the form and set their DataSource and DataField properties. While your at it, drop on a DBNavigator and set its DataSource. That's all it takes to build a fully functional database application supporting data display, record navigation, and data editing!

The Database Form Wizard

C++Builder provides a very powerful tool that can streamline even the minimal steps described above and allow you to build fully functional database applications with a few mouse clicks.

The Database Form Wizard is a great utility that comes with C++Builder that can make the development of database forms a breeze. By following the prompts you can design simple single table forms or even one-to-many forms using the Wizard. It even works on remote server tables! The Wizard produces professional looking forms - the basis on which to build an application. Customization is, of course, fully supported whether involving adding code, error checking, or providing custom lookups. The Wizard is extremely successful at meeting most needs for common database application development tasks.

Conclusion

C++Builder offers the client/server database applications developer a plethora of tools, components and options. With this rich set of features, virtually any database application can be written in C++Builder.


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