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Help / WLanguage / WLanguage properties / HFSQL properties
  • How to know whether a data file supports the management of NULL value?
  • Limits
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Stored procedures
The Null property is used to manage the NULL value in items of HFSQL data files or in items of data files accessed via Native Connectors.
This property is used to:
  • Assign NULL to the item for the current record.
  • Find out whether the item is associated with the NULL value for the current record.
  • Define the default value of an item when the item is described programmatically. You can also use the DefaultValue property.
Management of nullable values If the "Allow nullable types" option is checked in the project description, this property is no longer required to find out or modify the value of the item. This option allows you to:
  • directly assign a Null value to an HFSQL item using the following syntax:
    File.Item = Null
  • check whether an HFSQL item holds a Null value using the following syntax:
    IF File.Item = Null THEN
    ...
    END
For more details, see NULL value management: Allow null types.
Example
// Assign NULL to the Customer.CellPhone item
Customer.CellPhone.Null = True
Syntax

Find out if the field is associated with a NULL value Hide the details

<Result> = <Data file>.<Item>.Null
<Result>: Boolean
  • True if the item associated with the current record has a NULL value,
  • False otherwise.
<Data file>: Character string
Logical name of the data file used. This name was defined in the data model editor or with the File Description type.
<Item>: Character string
Name of the item used.
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Assigning NULL to an item Hide the details

<Data file>.<Item>.Null = <Null value>
<Data file>: Character string
Logical name of the data file used. This name was defined in the data model editor or with the File Description type.
<Item>: Character string
Name of item used.
<Null value>: Boolean
  • True to assign NULL to the specified item for the current record.
  • False otherwise.
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Defining the default value of an item in a file defined programmatically Hide the details

<Data file>.<Item>.Null = <Null value>
<Data file>: Character string
Logical name of the data file used. This name is defined with the File Description type.
<Item>: Character string
Name of item used.
<Null value>: Boolean
  • True if the default value of item must be null,
  • False otherwise.
Remarks

How to know whether a data file supports the management of NULL value?

  • To determine if a data file allows the use of the NULL value, use the NullSupported property.
  • To determine if am item allows the use of the NULL value, use the NullAllowed property.
Caution:
  • Assigning the property Null property on a data file or field that does not support NULL value management is prohibited: a fatal error is displayed.
  • Reading the Null property on a data file or item that does not support the NULL value always returns False.
For more details on how to use NULL values in data files and items, see NULL values in HFSQL.

Limits

  • The NULL value cannot be used:
    • on array items.
    • on automatic identifiers.
    • on composite keys.
  • The NULL value cannot be assigned several times to an item that takes the management of duplicates into account.
Minimum version required
  • Version 9
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Last update: 12/05/2024

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