Persistent Field Components

From RAD Studio
Jump to: navigation, search

Go Up to Working with Field Components Index

By default, dataset fields are dynamic. Their properties and availability are automatically set and cannot be changed in any way. To gain control over a field's properties and events you must create persistent fields for the dataset. Persistent fields let you:

  • Set or change the field's display or edit characteristics at design time or runtime.
  • Create new fields, such as lookup fields, calculated fields, and aggregated fields, that base their values on existing fields in a dataset.
  • Validate data entry.
  • Remove field components from the list of persistent components to prevent your application from accessing particular columns in an underlying database.
  • Define new fields to replace existing fields, based on columns in the table or query underlying a dataset.

At design time, you can - and should - use the Fields editor to create persistent lists of the field components used by the datasets in your application. Persistent field component lists are stored in your application, and do not change even if the structure of a database underlying a dataset is changed. Once you create persistent fields with the Fields editor, you can also create event handlers for them that respond to changes in data values and that validate data entries.

Note: When you create persistent fields for a dataset, only those fields you select are available to your application at design time and runtime. At design time, you can always use the Fields editor to add or remove persistent fields for a dataset.

All fields used by a single dataset are either persistent or dynamic. You cannot mix field types in a single dataset. If you create persistent fields for a dataset, and then want to revert to dynamic fields, you must remove all persistent fields from the dataset. For more information about dynamic fields, see Dynamic Field Components.

Note: One of the primary uses of persistent fields is to gain control over the appearance and display of data. You can also control the appearance of columns in data-aware grids. To learn about controlling column appearance in grids, see Creating a Customized Grid.

The following topics describe how to use the Fields editor to create or modify the persistent fields in a dataset, and how to work with persistent fields:

See Also