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GUID - Globally Unique IDentifier
In Delphi, GUID values are represented with the TGuid record defined in the System unit. A Guid value is a 128-bit integer (16 bytes) that can be used in database applications when a unique identifier is required.
When developing database applications, the TGuidField is used to represents a guid field in a dataset.
To create a sample GUID, hit CTRL + SHIFT + G in the code editor, this will create a unique GUID value, like this one: ['{B54ED86E-211F-4803-AF46-0586DA66C583}']. Each time you press CTRL + SHIFT + G, you'll get a new Guid value.
A Guid value can be converted from a string constant in the following form 'xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx', in which each x is a hexadecimal digit in the range 0-9 or A-F. For example, '123ABC45-65DE-F0F0-4242-A1B2C3D4E5F699' is a valid uniqueidentifier value.
TGuidEx
To ease the process of manipulating GUID values (in database applications), I've created a simple wrapper class arround the TGuid record. The TGuidEx class provides only class methods (can be called without actually creating and freeing the class).
Here's an example of usage:
Let's say you have a database TABLE with a uniqueidenitier type FIELD "ID".
1. To insert a new row into the TABLE, you can use the next SQL statement:
'insert into TABLE (ID, ...) values (" + TGuidEx.ToQuotedString(TGuidEx.NewGuid) +',...)';
2. To check if a TGuidField is "empty", use
var
guid : TGuid;
begin
guid := TGuidField(DataSet.FieldByName('ID')).AsGuid;
if TGuidEx.IsEmptyGuid(guid) then
ShowMessage('Value is "Empty"');
Here's the full source code (download):
unit GuidEx;
interface
uses SysUtils;
type
TGuidEx = class
//Creates and returns a new globally unique identifier
class function NewGuid : TGuid;
//sometimes we need to have an "empty" value, like NULL
class function EmptyGuid : TGuid;
//Checks whether a Guid is EmptyGuid
class function IsEmptyGuid(Guid : TGuid) : boolean;
//Convert to string
class function ToString(Guid : TGuid) : string;
//convert to quoted string
class function ToQuotedString(Guid : TGuid) : string;
//return a GUID from string
class function FromString(Value : string) : TGuid;
//Indicates whether two TGUID values are the same
class function EqualGuids(Guid1, Guid2 : TGuid) : boolean;
end;
implementation
{ TGuidEx }
class function TGuidEx.EmptyGuid: TGuid;
begin
result := FromString('{00000000-0000-0000-0000-000000000000}');
end;
class function TGuidEx.EqualGuids(Guid1, Guid2: TGuid): boolean;
begin
result := IsEqualGUID(Guid1, Guid2);
end;
class function TGuidEx.FromString(Value: string): TGuid;
begin
result := StringToGuid(Value);
end;
class function TGuidEx.IsEmptyGuid(Guid : TGuid): boolean;
begin
result := EqualGuids(Guid,EmptyGuid);
end;
class function TGuidEx.NewGuid: TGuid;
var
Guid : TGuid;
begin
CreateGUID(Guid);
Result := Guid;
end;
class function TGuidEx.ToQuotedString(Guid: TGuid): string;
begin
result := QuotedStr(ToString(Guid));
end;
class function TGuidEx.ToString(Guid: TGuid): string;
begin
result := GuidToString(Guid);
end;
end.//GuidEx
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