TCustomBufDataset¶

Dataset connected to a database.

Declaration¶

Source position: bufdataset.pas line 462

type

  TCustomBufDataset = class(TDBDataset)
  public
    constructor Create;
    function GetFieldData(Field: TField; Buffer: Pointer; 
                     NativeFormat: Boolean) : Boolean;
    function GetFieldData(Field: TField; Buffer: Pointer) : Boolean;
    procedure SetFieldData(Field: TField; Buffer: Pointer; 
                      NativeFormat: Boolean);
    procedure SetFieldData(Field: TField; Buffer: Pointer);
    procedure ApplyUpdates; overload;
    procedure ApplyUpdates(MaxErrors: Integer); overload;
    procedure MergeChangeLog;
    procedure RevertRecord;
    procedure CancelUpdates;
    destructor Destroy;
    function Locate : Boolean;
    function Lookup : Variant;
    function UpdateStatus : TUpdateStatus;
    function CreateBlobStream : TStream;
    procedure AddIndex;
    procedure ClearIndexes;
    procedure SetDatasetPacket;
    procedure GetDatasetPacket;
    procedure LoadFromStream;
    procedure SaveToStream;
    procedure LoadFromFile;
    procedure SaveToFile;
    procedure CreateDataset;
    procedure Clear;
    function BookmarkValid : Boolean;
    function CompareBookmarks : LongInt;
    procedure CopyFromDataset;
    property ChangeCount: Integer; {r}
    property MaxIndexesCount: Integer; {rwd}
    property ReadOnly: Boolean; {rwd}
    property ManualMergeChangeLog: Boolean; {rwd}
  published
    property FileName: TFileName; {rw}
    property PacketRecords: Integer; {rwd}
    property OnUpdateError: TResolverErrorEvent; {rw}
    property IndexDefs: TIndexDefs; {r}
    property IndexName: string; {rw}
    property IndexFieldNames: string; {rw}
    property UniDirectional: Boolean; {rwd}
  end;

Inheritance¶

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¶

Member	Visibility	Description
ChangeCount read only	public	Number of pending changes for the dataset.
FileName	published	File name on the local file system used to load or store the dataset.
IndexDefs read only	published	Index definitions for the dataset.
IndexFieldNames	published	Field names included in the custom index.
IndexName	published	Name of the selected index for the dataset.
ManualMergeChangeLog	public	Indicates if the update change log can be manually merged.
MaxIndexesCount	public	Maximum number of indexes available in the dataset.
PacketRecords	published	Number of records allowed in a data packet handled by the packet reader.
ReadOnly	public	Indicates if records can be added, deleted, or modified in the dataset.
UniDirectional	published	Indicates if the dataset is for uni-directional navigation only.

See all Properties

Methods¶

Member	Visibility	Description
AddIndex	public	Adds an index definition to the dataset.
ApplyUpdates	public	Applies pending updates to the dataset.
BookmarkValid	public	Determines if the specified Bookmark is valid for the dataset.
CancelUpdates	public	Cancels pending updates in the dataset.
Clear	public	Clears the content in the dataset.
ClearIndexes	public	Clears index storage in the dataset.
CompareBookmarks	public	Gets the relative sort order for the specified Bookmarks.
CopyFromDataset	public	Loads field definitions and optional data from another dataset.
Create	public	Constructor for the class instance.
CreateBlobStream	public	Create blob stream.
CreateDataset	public	Creates the dataset using its field definitions or bound fields.
Destroy	public	Free a TDataset instance.
GetDatasetPacket	public	Builds a data packet representing the content in the buffered dataset.
GetFieldData	public	Get the data for a field.
LoadFromFile	public	Loads the dataset from the specified file using the given format.
LoadFromStream	public	Loads the dataset from the specified stream using the given data format.
Locate	public	Locate a record based on some key values.
Lookup	public	Search for a record and return matching values.
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.
SaveToFile	public	Saves the dataset to the specified file using the given data format.
SaveToStream	public	Saves the dataset to the specified stream using the given data format.
SetDatasetPacket	public	Retrieves and applies the data packet with the content for the dataset.
SetFieldData	public	Store the data for a field.
UpdateStatus	public	Get the update status for the current record.

See all Methods

Events¶

Member	Visibility	Description
OnUpdateError	published	Event handler signalled when an error occurs while updating records.

See all Events

Name	Description
TBufDataset	Implements a database-aware buffered dataset.
TDBDataset	Dataset connected to a database.
TDataset	Base class for records-based data-access.