TCustomBufDataset class

In unit BufDataset

Ancestor class for a database-aware buffered dataset.

Declaration

pascal

TCustomBufDataset = class(TDBDataset)

Inheritance

Descends from it: TBufDataset TCustomSQLQuery

Description

TCustomBufDataset is a TDBDataset descendant that implements the ancestor class for a database-aware buffered dataset. TCustomBufDataset is an in-memory dataset that can be used as a local stand-alone dataset, or it can be used as a local buffer for updates applied to a remote dataset. TCustomBufDataset implements many features similar to those in TClientDataset in Delphi. However, it is not meant to be code or function compatible with TClientDataset. It is designed to provide management of the buffers used to access record data, and is used as the ancestor for classes like TSQLQuery and TRESTBufDataset.

As a TDBDataset descendant, it offers access to many of the database features supported in the FCL DB package. As a TDataset descendant, it also offers access to familiar navigation and data handling methods in the ancestor class. TCustomBufDataset has features that allow local storage and retrieval of field definitions and record data. In addition, facilities are provided that allow local indexing of record data in the dataset. There is a comprehensive parser/expression evaluator available that allows complete support for Filters in the dataset.

Do not create instances of TCustomBufDataset. Use the TBufDataset descendant instead.

Additional information about using TBufDataset can be found on the Lazarus Wiki at: How to write in-memory database applications in Lazarus/FPC (TBufDataset).

Properties

`Refreshing`	protected	Indicates if the Refresh method has been called but has not completed.
`ChangeCount`	public	Number of pending changes for the dataset.
`MaxIndexesCount`	public	Maximum number of indexes available in the dataset.
`ReadOnly`	public	Indicates if records can be added, deleted, or modified in the dataset.
`ManualMergeChangeLog`	public	Indicates if the update change log can be manually merged.
`FileName`	published	File name on the local file system used to load or store the dataset.
`PacketRecords`	published	Number of records allowed in a data packet handled by the packet reader.
`IndexDefs`	published	Index definitions for the dataset.
`IndexName`	published	Name of the selected index for the dataset.
`IndexFieldNames`	published	Field names included in the custom index.
`UniDirectional`	published	Indicates if the dataset is for uni-directional navigation only.

Methods

`DefaultReadFileFormat`	protected
`DefaultWriteFileFormat`	protected
`DefaultPacketClass`	protected
`CreateDefaultPacketReader`	protected
`SetPacketRecords`	protected	Sets the value for the PacketRecords property.
`SetRecNo`	protected	Sets the value for the RecNo property.
`GetRecNo`	protected	Gets the value for the RecNo property.
`GetChangeCount`	protected	Gets the value for the ChangeCount property.
`AllocRecordBuffer`	protected	Allocates resources for a record buffer.
`FreeRecordBuffer`	protected	Frees resources allocated for the specified record buffer.
`ClearCalcFields`	protected	Clears calculated fields in the specified record buffer.
`InternalInitRecord`	protected	Performs actions needed to initialize the buffer for a record in the dataset.
`GetCanModify`	protected	Gets the value for the CanModify property.
`GetRecord`	protected	Gets the record buffer for the record at the specified relative position.
`DoBeforeClose`	protected	Performs actions needed prior to closing the dataset.
`InternalInitFieldDefs`	protected	Performs actions needed to initialize field definitions for the dataset.
`InternalOpen`	protected	Performs actions needed to open the dataset.
`InternalClose`	protected	Performs actions needed to close the dataset.
`GetRecordSize`	protected	Gets the value for the RecordSize property.
`InternalPost`	protected	Performs actions needed to post a record to the dataset.
`InternalCancel`	protected	Performs actions needed to cancel a pending update in the dataset.
`InternalDelete`	protected	Performs actions needed to delete the current record in the dataset.
`InternalFirst`	protected	Performs actions needed to move to the first record in the dataset.
`InternalLast`	protected	Performs actions needed to move to the last record in the dataset.
`InternalSetToRecord`	protected	Moves the dataset to the specified record buffer.
`InternalGotoBookmark`	protected	Performs actions needed to move to the specified Bookmark in the dataset.
`SetBookmarkData`	protected	Stores the specified Bookmark data to a record buffer.
`SetBookmarkFlag`	protected	Stores the specified Bookmark flag value to a record buffer.
`GetBookmarkData`	protected	Gets bookmark data from the specified record buffer.
`GetBookmarkFlag`	protected	Gets Bookmark flag data from the specified record buffer.
`IsCursorOpen`	protected	Indicates if the cursor for the dataset has been opened.
`GetRecordCount`	protected	Gets the value for the RecordCount property.
`ApplyRecUpdate`	protected	Raises an exception. ApplyRecUpdate is not supported in TCustomBufDataset and descendent classes.
`ApplyRecUpdateEx`	protected
`SetOnUpdateError`	protected	Sets the value for the OnUpdateError property.
`SetFilterText`	protected	Sets the value in the Filter property.
`SetFiltered`	protected	Sets the value in the Filtered property.
`InternalRefresh`	protected	Performs actions needed to refresh records in the dataset.
`DataEvent`	protected	Triggers an event when the dataset or its data is modified.
`GetNewBlobBuffer`	protected	Creates a new Blob buffer and adds it to the internal Blob buffers member.
`GetNewWriteBlobBuffer`	protected	Creates a new Blob update buffer and adds it to the internal list.
`FreeBlobBuffer`	protected	Frees resources allocated to the specified Blob buffer.
`InternalAddIndex`	protected	Performs actions needed to add an index to the dataset.
`BeforeRefreshOpenCursor`	protected	An empty implementation in TCustomBufDataset.
`DoFilterRecord`	protected	Performs actions needed to filter records in the dataset.
`SetReadOnly`	protected	Sets the value in the ReadOnly property.
`IsReadFromPacket`	protected	Indicates if dataset content was read from a data packet reader or file.
`getnextpacket`	protected	Reads and applies the next data packet from the data packet reader.
`GetPacketReader`	protected	Gets a Data Packet Reader using the specified data format for the dataset.
`Fetch`	protected	An empty implementation in TCustomBufDataset.
`LoadField`	protected	An empty implementation in TCustomBufDataset.
`LoadBlobIntoBuffer`	protected	Loads a Blob buffer for the specified field into the current record buffer.
`DoLocate`	protected
`Create`	public	Constructor for the class instance.
`GetFieldData`	public	Get the data for a field.
`SetFieldData`	public	Store the data for a field.
`ApplyUpdates`	public	Applies pending updates to the dataset.
`MergeChangeLog`	public	Frees update buffers and Blob update buffer allocated for the dataset.
`RevertRecord`	public	Reverts the current record to its original (un-edited) values.
`CancelUpdates`	public	Cancels pending updates in the dataset.
`Destroy`	public	Destructor for the class instance.
`Locate`	public	Locates the first record with fields having the specified values.
`Lookup`	public	Gets values from the first record with fields that match the search condition.
`UpdateStatus`	public	Gets the update status for the current record in the dataset.
`CreateBlobStream`	public	Creates a Blob stream for the specified field with the given permissions.
`AddIndex`	public	Adds an index definition to the dataset.
`ClearIndexes`	public	Clears index storage in the dataset.
`SetDatasetPacket`	public	Retrieves and applies the data packet with the content for the dataset.
`GetDatasetPacket`	public	Builds a data packet representing the content in the buffered dataset.
`LoadFromStream`	public	Loads the dataset from the specified stream using the given data format.
`SaveToStream`	public	Saves the dataset to the specified stream using the given data format.
`LoadFromFile`	public	Loads the dataset from the specified file using the given format.
`SaveToFile`	public	Saves the dataset to the specified file using the given data format.
`CreateDataset`	public	Creates the dataset using its field definitions or bound fields.
`Clear`	public	Clears the content in the dataset.
`BookmarkValid`	public	Determines if the specified Bookmark is valid for the dataset.
`CompareBookmarks`	public	Gets the relative sort order for the specified Bookmarks.
`CopyFromDataset`	public	Loads field definitions and optional data from another dataset.