HDescribeConnection (Function)

ONLINE HELP
WINDEV, WEBDEV AND WINDEV MOBILE

Version:

Home | Sign in | English

Help / WLanguage / Managing databases / HFSQL / HFSQL functions

Syntax 1: Using a character string for the OLE DB provider
Syntax 1: Pseudo-connection to HFSQL Classic database
Differences between HOpenConnection and HDescribeConnection
Using the Native xBase Connector with non-Latin character sets
UDL file
Native MySQL Connector

WINDEV

WEBDEV

WINDEV Mobile

Others

See also

HDescribeConnection (Function)

In french: HDécritConnexion

Not available with this kind of connection

Describes a new connection to an external database. This connection is named. Specific parameters can be defined such as the management mode of cursors (if the accessed database allows it).

To associate this connection with a table or a data file, use HChangeConnection.

To open the connection, use HOpenConnection. If the connection parameters described by HDescribeConnection are incorrect, HOpenConnection will return an error.

With HDescribeConnection, an Oracle table description imported into the analysis can be directly used by HFSQL Classic data files. Simply describe a temporary connection to an HFSQL Classic database and associate it with the file description from in the analysis. See the Examples for more details.

This function is kept for backward compatibility. We recommend that you use a Connection variable and its properties to describe a connection.

Example

See additional examples

HDescribeConnection("MyConnection", "", "", ...
"Server_SQLServer", "dbo", hNativeAccessSQLServer, hOReadWrite, "")

Syntax

Describing a connection through programming Hide the details

<Result> = HDescribeConnection(<Connection> , <User> [, <Password>] , <Data source> , <Database> , <OLE DB provider or Native Connector> [, <Access> [, <Extended information>]] , <Additional options>)

<Result>: Boolean

True if the operation was performed,
False if a problem occurs. HErrorInfo is used to identify the error.
To establish this connection, use HOpenConnection (this function will return an error if the connection parameters are incorrect).
To assign this connection to a data file, use HChangeConnection.

<Connection>: Character string

Name of new connection to define.
If this name is already used by an existing connection, the former connection is replaced with the new one. The former connection (as well as the data files that used it) are automatically closed.

<User>: Character string

Username used for the database. This parameter is returned by the CtUserName property.

<Password>: Optional character string

Connection password (if this password exists). If no password is required, use an empty string ("") or the NULL keyword.

<Data source>: Character string

Full path of the data source. The connection will be created and opened for this data source. This parameter is returned by the CtDatabase property.
XML: This parameter corresponds to the name of XML file.
This parameter corresponds to the server name. The port number used by the HFSQL server can be specified. The port 4900 will be used by default. If the port number of the HFSQL server is different, use the following notation:
<Computer name>: <Port number>
Example: "ComputerName:4901".
For a use via Internet, the ports must be managed by Firewall. For more details, see Managing ports.
You have the ability to specify an IPv6 address by writing the IPv6 address between square brackets. In this case, the port number must be specified after the closing square bracket. For example: [0154:2145:2155::5554]:4900.

Access by JDBC:
This parameter corresponds to URL for connecting to the database.
Depending on the JDBC driver used, the database name must be specified in the connection URL.

<Database>: Character string

Name of database that will be used on the data source, empty string ("") if no name must be specified. This parameter can be used if the data source allows you to specify the database that must be used.
For example, on SQL Server, the "Master" database is the default database but other databases can be handled ("dbo" for example).
To specify that the access is performed on a file found in the "dbo" database (that is not the default database), <Database> must correspond to "dbo".
This parameter is returned by the CtInitialCatalog property.

<OLE DB provider or Native Connector>: Character string or constant

Name of OLE DB provider used. To easily retrieve the string to use, select "Connection" in the data model editor (see the Notes).

or
one of the following constants:
hAccessHF7 Pseudo-connection to HFSQL Classic database
hAccessHFClientServer Native Connector to an HFSQL Client/Server database.
hNativeAccessAS400 Native AS/400 Connector (optional module of WINDEV/WEBDEV)
hNativeAccessDB2 Native DB2 Connector (optional module of WINDEV/WEBDEV)
hNativeAccessInformix Native Informix Connector (optional module of WINDEV/WEBDEV)
hNativeAccessMariaDB Native MariaDB Connector (optional module of WINDEV/WEBDEV)
hNativeAccessMySQL Native MySQL Connector (optional module of WINDEV/WEBDEV)
hNativeAccessOracle Native Oracle Connector (optional module of WINDEV/WEBDEV)
hNativeAccessOracleLite Native Oracle Connector (optional module of WINDEV Mobile)
hNativeAccessPostgreSQL Native PostgreSQL Connector (optional module of WINDEV/WEBDEV)
hNativeAccessProgress Native Progress Connector (optional module of WINDEV/WEBDEV)
hNativeAccessSQLAzure Native SQL Azure Connector (optional module of WINDEV/WEBDEV, provided with Native SQL Server Connector)
hNativeAccessSQLite Native SQLite Connector (provided with WINDEV/WEBDEV)
hNativeAccessSQLServer Native SQL Server Connector (optional module of WINDEV/WEBDEV).
The former Native Connector is used by default. To use the new Native SQL Server Connector, use the H.SQLServerMode variable.
hNativeAccessSQLServerMobile Native SQL Server Mobile Connector (optional module of WINDEV Mobile)
hNativeAccessSybase Native Sybase Connector (optional module of WINDEV/WEBDEV)
hNativeAccessXBase Native xBase Connector (included with WINDEV/WEBDEV)
hNativeAccessXML Native XML Connector (included with WINDEV/WEBDEV)
hODBC OLE DB provider for ODBC (used to access an ODBC data source declared in the ODBC data sources of Windows)
hOledbAccess97 OLE DB provider for Access 97
hOledbAccess2000 OLE DB provider for Access 2000
hOledbDBase5 OLE DB provider for dBase 5
hOledbExcel97 OLE DB provider for Excel 97
hOledbExcel2000 OLE DB provider for Excel 2000
hOledbLotus4 OLE DB provider for Lotus 4
hOledbOracle OLE DB provider for Oracle
hOledbSQLServer OLE DB provider for SQL Server

Caution: To use an OLE DB connection, you must:
install MDAC version 2.6 or later (setup performed by WINDEV/WEBDEV and when creating the client version)
install the OLE DB provider corresponding to the database used.
This parameter is returned by the CtOLEDBProvider property.

The available constants are as follows:
hAccessHF7 Pseudo-connection to HFSQL Mobile database
hAccessHFClientServer Connection to an HFSQL Client/Server database
hAccessJDBCMySQL Access to MySQL database via JDBC
hAccessJDBCSQLite Access to SQLite database via JDBC
hAccessJDBCSQLServer Access to SQL Server database via JDBC

<Access>: Optional constant

Configures the type of access to the database.
hORead The database can be accessed in read-only. You can only read records. No record can be added or deleted.
hOReadWrite
(default value) The database can be accessed in read/write. You can read and write new records.

This parameter is returned by the CtAccess property.
Access by JDBC: This parameter is ignored.

<Extended information>: Optional character string

Optional information inserted into the string for connecting to the database. If specific keywords are recognized, the corresponding information is extracted from the connection string. The rest of the connection string is sent to the database. Then, the extracted parameters are processed by the Native Connector or by the OLE DB connector used.
These keywords must be indicated as follows: "<Keyword> = <Value>;".
You can for example specify "Trusted_Connection=YES" in order to use a connection with authentication via the NT login.
The keywords recognized by OLE DB and the Native Connectors are presented in the Optional connection information page.
Example of string to use:
"WD Cache Size = 10000; Server Port=3306;"

Keywords recognized for the access by HFSQL Client/Server:
COMPRESSION Enables or disables the compression of data exchanged between Client and Server. This keyword can correspond to:
TRUE to enable the data compression.
FALSE to disable the data compression.
DB_EXIST Checks the existence of the database. If the specified database does not exist, HDescribeConnection returns False.
ENCRYPTION Enables the encryption of data exchanged between Client and Server. This keyword can take several values:
FAST
RC5_16 to use 16-round RC5 encryption.
AES128 to use 128-bit AES encryption with the OFB mode of operation.
AES192 to use 192-bit AES encryption with the OFB mode of operation.
AES256 to use 256-bit AES encryption with the OFB mode of operation.

This parameter is returned by the CtExtendedInfo property.
HFSQL database accessed via a RMI server: This parameter corresponds to the address of RMI server and to the port used. The following format must be used: "RMI=<Server address>:<Port number>". For example: "RMI=192.168.52.148:1099".
Access by JDBC: This parameter is mandatory. It must correspond to the full name of JDBC driver to use. This name is case sensitive.

<Additional options>: Constant

If this parameter is not specified, the HFSQL engine automatically defines the best parameters to use according to the database accessed and to the OLE DB provider used.
To force some parameters, you have the ability to combine the following constants:
Location of cursors
hClientCursor Cursor managed by MDAC. Offers more features than a server cursor. A client cursor must necessarily be a static cursor.
hServerCursor Cursor managed by the database. This cursor can easily apply the changes performed by the other users to the data.
Type of cursor
hDynamicCursor Cursor offering a lot of features but consuming a lot of memory. This cursor allows all types of moves. It allows you to access all the modifications, additions and deletions performed by the other users.
hForwardOnlyCursor Fast cursor consuming little memory. The move is performed from the first record to the last one. The data modified by the other users is not visible.
hOpenKeysetCursor Cursor that handles a fixed set of records. Only the keys corresponding to the record are stored and not the records (consumes less memory). The deleted records can no longer be accessed. Modifications performed by other users are visible (but records added are not).
hStaticCursor Makes a copy of all query records in memory (high memory usage). All types of moves are allowed.
Lock mode
hOptimisticCursor The record is locked when it is updated
hPessimisticCursor The record is locked as soon as it goes into edit mode to be modified.
hReadOnlyCursor The set of records cannot be modified.
Caution: some types of cursors may not be supported by all the OLE DB providers.
This parameter is returned by the CtCursorOptions property.

Describing a connection from an ADO connection string Hide the details

<Result> = HDescribeConnection(<Connection> , <ADO connection string> [, <Access>])

<Result>: Boolean

True if the operation was performed,
False if a problem occurs. HErrorInfo is used to identify the error.

<Connection>: Character string

Name of new connection to define. If this name is already used by an existing connection, the former connection is replaced with the new one. The former connection (as well as the data files that used it) are automatically closed.

<ADO connection string>: Character string

ADO connection string used. For more details on the syntax of this connection string, see the documentation of the OLE DB provider used.

<Access>: Optional constant

Configures the type of access to the database.
hORead The database can be accessed in read-only. You can only read records. No record can be added or deleted.
hOReadWrite
(default value) The database can be accessed in read/write. You can read and write new records.

Remarks

Syntax 1: Using a character string for the OLE DB provider

To easily find the character string that must be used to define the OLE DB provider, we recommend that you proceed as follows:

In the data model editor, open the connection description window: on the "Analysis" tab, in the "Connections" group, click "Connections".
Select the provider to use ("Connect via" combo box).
The character string corresponding to the provider is displayed. This character string can be used to define the OLE DB provider used in <OLE DB provider>.

Syntax 1: Pseudo-connection to HFSQL Classic database

OLE DB data files or native data files are described in the data model editor. To handle these descriptions through programming with an HFSQL database, simply specify the hAccessHF7 constant as provider name.

Then, this connection can be assigned to the data files affected by HChangeConnection.

The data files in HFSQL format corresponding to the description of the OLE DB or native files will be created (if necessary) in the directory defined by <Data source>. By default, these data files are empty when they are created.

Differences between HOpenConnection and HDescribeConnection

Method 1: To open a connection at the start of the application and close it at the end, use HOpenConnection. To use this connection when handling data files or tables, simply change this connection with HChangeConnection.

HOpenConnection(MyConnection, params) // open the connection
HChangeConnection(AFile, MyConnection)

Method 2: To describe a connection through programming and to automatically open it when opening the data file, you must:

describe the connection with HDescribeConnection.
associate this connection with the desired data file description using HChangeConnection. The connection will only be opened the first time the data file is accessed.

This solution can be useful when an application handles both HFSQL data files and Oracle data files. For example, if the application uses a single Oracle file, in a specific process, the connection to the Oracle database will only be made if necessary.

If the first solution is chosen for the same type of application, the connection (that may take quite a long time) will be established whenever the application is started.

Example:

HDescribeConnection(MyConnection, params)
HChangeConnection(AFile, MyConnection)
...
HReadFirst(AFile) // Open the connection
...
HClose(AFile) // Close the connection

Using the Native xBase Connector with non-Latin character sets

To use the Native xBase Connector with non-Latin character sets, a standard OEM/ANSI conversion must be performed by the Native Connector. To do so, the following string must be specified in the extended information:

OEMTOANSI=WINDOWS;

Example:

In the initialization code of the project, add the code used to modify the character set:
ChangeCharset(charsetChinese)
Create an xBase connection:
HDescribeConnection("CntxBase", "", "", fExeDir(), "", hNativeAccessXBase, hOReadWrite, ...
"OEMTOANSI=WINDOWS;")
HChangeConnection("*", "CntxBase")

UDL file

To create a UDL file:

Create a text file whose extension is "UDL".
Double-click this file. The window for the properties of the data links is opened.
Configure the connection.
Run the test of the connection.
Validate ("OK" button). The UDL file can now be used.

Native MySQL Connector

To get the latest MySQL features (e.g. new default access mode), you need to update the MySQL client library (LibMySQL.DLL file).. For more details, see Native MySQL Connector.

Business / UI classification: Business Logic

Component: wd300hf.dll