NullAllowed (Property)

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

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How to know whether a data file supports the management of NULL value?
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NullAllowed (Property)

In french: NullAutorisé

Available only with these kinds of connection

..NullAllowed is used to manage the NULL value in the items of HFSQL data files.

This property is used to:

Find out the management mode of the NULL value for an item of a data file described in the data model editor.
Define the management mode of the NULL value when an item of a data file is described by programming.

If a data file supports the NULL value and if its item allows the management of NULL, you will have the ability to use ..Null to assign NULL to the item for the current record for example.

..NullAllowed is useful to prevent from using the NULL value for some items found in a data file defined by programming (this file supporting the NULL value).

Remark: From version 19, HFSQL is the new name of HyperFileSQL.

Syntax

Finding out whether the item allows the management of the NULL value Hide the details

<Result> = <Data file>.<Item>..NullAllowed

<Result>: Boolean

True if the item allows the management of the NULL value,
False if the item does not support the management of the NULL value.

<Data file>: Character string (with or without quotes)

Logical name of data file used. This name was defined in the data model editor or by the File description type.

<Item>: Character string (with or without quotes)

Name of item used. This name was defined in the data model editor or by the Item description type.

Defining the management mode of the NULL value for the item Hide the details

<Item>..NullAllowed = <Management mode>

<Item>: Character string (with or without quotes)

Name of item used. This name was defined by the Item description type.

<Management mode>: Boolean

True to manage the NULL value,
False not to support the NULL value.

Remarks

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

To find out whether a data file allows (or not) the management of the NULL value, use ..NullSupported.

Caution:

..Null cannot be assigned to a data file or an item that does not support the management of NULL value: a fatal error occurs.
Using ..Null on a data file or item that does not support the management of NULL value always returns False.

Limits

The NULL value cannot be used:

on the array items.
on the automatic identifiers.
on the composite keys.