Assigns a unique identifying number to any database object. The
GUID data type is a 16 byte binary data type. This data type is
used for the global identification of objects, programs, records,
and so on. The important property of a GUID is that each value is
globally unique. The value is generated by an algorithm, developed
by Microsoft, which assures this uniqueness.
The GUID is a 16-byte binary data type that can be logically
grouped into the following subgroups:
4byte-2byte-2byte-2byte-6byte.
The standard textual representation is
{12345678-1234-1234-1234-1234567890AB}.
The virtual table OLE Control (2000000042) does not use the GUID
data type. It uses a textual representation of the GUID in a text
field instead. It is easier to make operations and references to
this text field using the GUID data type than it is using the
textual representation. The GUID data type is compatible with the
existing textual representation.
The GUID data type is useful when you want to uniquely identify
some data, so that it can be exchanged with external applications.
For example, if you want to transfer an item catalog to an external
application, you add a GUID field to the record in the table and
use this as the primary reference when you communicate with the
external application.
Compatibility
You can assign and compare the TEXT data type and the GUID data
type. Assigning a GUID to a TEXT can be done as follows:
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MyTableRec.MyGuid := MyTableRec.MyText;
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Useful C/AL Functions and
Properties
The following C/AL functions can be used with the GUID data
type:
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Guid:=CREATEGUID();
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This function creates a new unique GUID value. The value can
then be assigned to a field of the GUID data type or of the TEXT
data type.
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Ok:=ISNULLGUID(Guid);
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This function is a convenient way to check if a value has
already been assigned to a GUID. A NULL GUID (consisting only of
zeroes) is valid, but should never be used for reference
purposes.
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CLEAR(Guid);
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The standard CLEAR function can also be used on the GUID data
type. It nullifies the GUID.
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AutoSplitKey
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A NULL GUID is valid but is not useful in a table. Therefore,
the AutoSplitKey property is implemented for the GUID data type
when it is used in a form. When GUID is selected as a primary key,
AutoSplitKey is enabled for the form, and the GUID value remains
NULL. When you create a new record, a valid GUID is created and
assigned automatically.
The CREATEGUID Function
(GUID) and ISNULLGUID Function
(GUID) functions are available in the C/AL Symbol Menu
under SYSTEM, Variables.
CREATEGUID takes no arguments and returns a valid 16-byte GUID
value. If the result is assigned to a TEXT variable or field, the
value is converted to a string and follows the syntax explained
earlier. The algorithm that generates the new GUID value uses
Microsoft's CoCreateGuid function.
ISNULLGUID takes a GUID value as a required argument and returns
TRUE/FALSE depending on whether the GUID value is NULL. This
function does not accept a TEXT value as an argument.
CLEAR is the standard CLEAR function and takes one required
argument. It nullifies the GUID value in the same way as it resets
any other value.
AutoSplitKey is a property, not a function and can be applied to
forms. If you have defined a GUID field as part of the primary key,
the AutoSplitKey property automatically generates a new valid GUID
value. When a new record is created and the GUID field is left as
NULL, the AutoSplitKey property ensures that a valid GUID value is
automatically inserted into the field. If you then enter a NULL
GUID into this record, for example, by using the CLEAR function,
this new NULL GUID value is not automatically replaced by the
AutoSplitKey property. The AutoSplitKey property only applies to
new records.
Format
The GUID value can also be represented as text. You can use the
standard C/AL functions FORMAT and EVALUATE to convert from GUID
values to TEXT values. If you do not use the correct format when
you edit a GUID value in its textual format, the following error
message is displayed:
Invalid Format of GUID string. The correct format of the GUID
string is {CDEF7890-ABCD-1234-ABCD-1234567890AB} where 0-9, A-F
symbolizes hexadecimal digits.
See Also
