HCreateIfNotFound (Function)

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Characteristics of created data file
Additional files created
Managing passwords
Managing fatal errors when creating a data file
Managing non-Latin character sets
Replication: Range of identifiers
Priority for defining the location of log files
Creating or opening an existing table
Managing indexes
Creating the data file from its description

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HCreateIfNotFound (Function)

In french: HCreationIfNotFound

Not available with this kind of connection

Performs the following operations:

If the data file does not exist, creates an empty data file (".FIC" extension) with the index file and the memo file if necessary.
The function is equivalent to HCreate.
If the data file exists, opens the data file.
In this case, the function is equivalent to HOpen.
To optimize the call to HCreateIfNotFound, the data file can be opened only when accessed for the first time (using the hDelayedOpening constant).

Remark: The automatic creation of non-existing data files can be enabled in the project description ("Files" tab of the project description, "Automatically create the data files when they are opened"). HCreateIfNotFound is automatically used if the data file does not exist when it is handled for the first time.

If the data file is logged, you can specify the location of the log files.

If integrity constraints have been defined and if they are supported, the links are updated by the server when creating the data file.

Example

See additional examples

// Création de tous les fichiers de données décrits dans l'analyse 
// avec le mot de passe "PSW"
HCreationIfNotFound("*", "PSW")

// Création du fichier de données Commande (décrit dans l'analyse)
HCreationIfNotFound(Commande)

Syntax

<Result> = HCreateIfNotFound([<Data file> [, <Password> [, <Path of the JNL file> [, <Path of the JournalOperation file>]]] [, <Option>]])

<Result>: Boolean

True if the data file was created or opened,
False if a problem occurs. HError is used to identify the error. If a fatal error occurs, a specific process is required to continue the program and to check whether the data file was created (see the Notes).

<Data file>: Optional character string

Name of data file to use.
If this name is not specified, HCreateIfNotFound will use the last data file used by the last HFSQL function (function starting with "H").
If this parameter is set to "*", all the data files in the current analysis will be created or opened. If a password is specified, this password is used for all the data files.
Projects with multiple analyses: All data files for all analyses will be created or opened.
This parameter can also correspond to the name of a group of files (or custom-folder) defined in the analysis (not available in Android and Android widget). If a password is specified, this password is used for all the data files of the group.
Caution: this parameter cannot be a variable of type File description.
The maximum number of files that can be simultaneously opened by an iPhone/iPad application cannot exceed 256. Therefore, up to 80 HFSQL files can be opened simultaneously (one ".fic" file, one ".ndx" file and one ".mmo" file for each HFSQL data file).

<Password>: Optional character string

Password associated with the data file.
Empty string ("") if no password is used.

<Path of the JNL file>: Optional character string

Access path to the JNL file associated with the logged data file. This parameter is only taken into account if the data file is logged. In this case, <File name>JNL.fic will be created at the specified location.
This parameter must not be specified. In HFSQL Client/Server, the path of JNL file is defined and it cannot be modified.
This parameter is ignored.
Access by JDBC: This parameter is ignored.

<Path of the JournalOperation file>: Optional character string

Access path to the JournalOperation file and to the JournalIdentification file associated with the logged data file. The JournalOperation file contains all the operations performed on the logged data file. This parameter is only taken into account if the data file is logged.
This parameter must not be specified. In HFSQL Client/Server, the path of operation file is defined and it cannot be modified.
This parameter is ignored.
Access by JDBC: This parameter is ignored.

<Option>: Optional constant

Optimize the opening of existing data files.
hChangeCharset The character set defined by ChangeCharset will be taken into account in the new data file. Sorts, searches or other types of operations performed on string keys (strings, characters, date and time) will use the new character set.
hDelayedOpening If the data file already exists, it will be opened during the first access to the data file. If the data file does not exist, it is created and opened.
This constant is only available for HFSQL Classic.
hNoLink Management of integrity: Links are not updated on the server (create, modify or delete).
Reminder: By default, the links are updated on the server when creating a data file.
This constant is only available for HFSQL Client/Server.

This parameter is ignored.
Access by JDBC: This parameter is ignored.
This parameter is ignored.

Remarks

Characteristics of created data file

The characteristics of created data file are as follows:

Name of the data file:
Physical name defined during the file description in the data model editor. This name can be modified by HChangeName before creating the data file.
Directory of data file:
Directory defined during the file description in the data model editor. This directory can be changed with HChangeDir and HSubstDir before creating the data file.
Remark: If the UAC is enabled (Windows Vista and later), the data location is specific: the data will not be located in the application directory, but in a specific Windows directory. In this case, you must create the application data directory (you can get the path with fDataDirUser).
The order of items created in the physical file is the physical order of items created in the analysis (and not the logical order).
Content of the data file:
The created data file is empty, which does not mean that its size is null (the file contains a header describing its structure).

Remark: If the data file already existed (same name, same directory), this data file is opened. If the hDelayedOpening constant is specified, the data file will only be opened the first time it is accessed (optimizes the speed of HCreateIfNotFound).

Additional files created

When creating a data file, the following files can be created in addition to the data file:

An index file (".NDX" extension) if one or more keys have been defined in the file description.
A memo file (".MMO" extension) if one or more memo items have been defined in the file description.
A log file (".JNL" extension). This file is created only if the corresponding option was selected during the file description (see next paragraph).
This file is not created.
A <ProjectName>.REP file. This file contains the list of data files handled by the application. This file is created (or filled) if the management of .REP is enabled (HSetREP). If the hDelayedOpening constant is specified, the .REP file will be updated during the automatic file opening performed during the first access to the data file. For more details, see .REP file.
This file is not created.

Managing passwords

The password can be defined:

when the data file is created or opened by HCreateIfNotFound.
before the data file is created by HPass.Caution: The password is independent of data encryption. The data encryption must be configured during the file description in the data model editor ("Details" tab).

The password is not associated with a data file but with a database. This password must be specified during the connection (HConnect).

Managing fatal errors when creating a data file

If a fatal error occurs when creating a data file, it may be interesting to continue the program while checking whether the data file was created or not. To do so, we recommend that you perform the following exception process:

WHEN EXCEPTION IN
	HCreateIfNotFound(PERE)
DO
	Error("Erreur HFSQL : " + HError())
ELSE
	Trace("fichier créé")
END

Managing non-Latin character sets

If the hChangeCharset constant is specified, the character set used in the data file will be the one specified by ChangeCharset. Sorts, searches, ... on string keys (strings, characters, date and time) will be performed according to this character set.

The character set used can be modified by HIndex.

Remark: the size of string items specified in the analysis is expressed in bytes and not in characters. Depending on the character set used, you may have to increase the item size (if the characters used are coded on 2 bytes for example).

For more details, see Managing specific character sets in the data files.

Replication: Range of identifiers

The automatic identifiers for the files of subscriber replicas are using a range of identifiers that differs from the one used by the file of master replica and by the other files of subscriber replicas.

This range of automatic identifiers is written in the header of each data file (".FIC" extension).
This range is initialized:

when creating a data file (HCreate, HCreateIfNotFound).
via WDReplic.
when HInitSubscriber is used.

For more details, see the consequences of implementing the replication.

Priority for defining the location of log files

The location of log files is defined according to the following priority order:

Location specified when creating the logged data file (HCreateIfNotFound).
Location specified by HChangeLogDir.
Location specified in the analysis.
Location of the logged data file.

If another application uses HDeclareExternal on a logged data file, the changes made by this application are saved in the log files specified in the header of the logged HFSQL data file.

The location of Log files is fixed and it cannot be modified. For more details, see Log files in Client/Server mode.

Creating or opening an existing table

If the table already exists, the table is opened.

If the table does not already exist, the table is created. When creating a table, WINDEV and WEBDEV try to create the items in the OLE DB type corresponding to the HFSQL type. If this type is not supported, the HFSQL engine successively tries all the "compatible" OLEDB types until it finds a type that is supported by the OLEDB database.

Managing indexes

HCreateIfNotFound does not return any error messages if an index cannot be added. The table is created without the index that is causing the problem. In this case, duplicates may be found in an item defined as unique key by WINDEV or WEBDEV if the external database does not support the unique keys.

Creating the data file from its description

The data file can be directly created from its description in the data model editor. To do so, select "Create the data file" from the popup menu of the data file (in the analysis graph) and select the directory in which the data file must be created.

Component: wd300hf.dll