Using the APPX/ODBC Connection

Introduction:

The APPX/ODBC Connection allows APPX Applications, through a Windows ODBC Server, to access and operate upon data stored in a non-APPX data format, such as SQL-Server or MS-Access' Jet database. ( If you're interested in accessing AppxIO data on an APPX/Server, from a non-APPX application such as Crystal Reports or MS-Access, see APPX/ODBC Server .)

APPX/ODBC is licensed separately, requiring its own product registration. You must have an ODBC Data Source (such as SQL-Server or Access) installed to use the ODBC Connection.

Setting up APPX/ODBC Connection:

Within Windows Control Panel, 32bit ODBC, 'System DSN' tab, create or determine the Data Source Name (DSN) you want to use.

Using the 'Configure' then 'Advanced' buttons, you may want to establish or identify a Login Name and Password. (Required for SQL-Server.)

If you have an ODBC client in addition to APPX (such as WinSQL), you may want to confirm you can access tables defined under this Data-Source/UserID/Password.

You may specify the System Data Source (DSN), table name mapping, and APPX record (row) level locking Database by creating an APPX File System Group. From the APPX Main Menu, this may be found in 3)System Administration, 2)Configuration, 3)File System Groups.

Entire Databases and/or individual files (tables) may be assigned to a File System Group. When you assign a Database to a File System Group, all files within that Database share the File System Group's specifications. You can assign an individual file to a File System Group using the Database Management's 2)File Specifications option.

As of APPX release 3.4 and higher, current FMS types are:

    1 - AppxIO (our proprietary ISAM) or VAX/RMS.
    2 - VISION (from AcuCobol)
    3 - CISAM (from Informix)
    4 - Sybase
    5 - Oracle
    6 - ODBC (for example, SQL-Server, Access, etc.)
    7 - APPX/NET remote AppxIO file server 

To store a file in an ODBC Database, go into 5)Database File Management, 2)File Specifications, change the FMS Attribute from '1' to '6'.

Then, establish the file's ODBC specifications by setting its 'FMS Group' Attribute to a valid FMS Group Name. The FMS Group is SCANable.

You can create and edit File System (FMS) Groups from within this SCAN. (Look in the upper right hand corner of the screen.)

Within the File System Group's "1)FMS Controls" must be defined:

    1) ODBC  [[#System Data Source][Data Source Information]] (DSN), 
    2)  [[#Table Names][Table Name mapping]] (table_name), and 
    3)  [[#Row Locking][Row Locking]] (proxy_db)

 

Example:

Below is an example of a complete FMS Control entry:

     DSN=local_sql_server; UID=sa; PWD=;: 
     table_name=$lcase($appl_$file):
     proxy_db=LOK:

The APPX/ODBC Connection interprets the above example as follows:

• Connect to an ODBC System Data Source named "local_sql_server". Provide a UserID of "sa", and no password.
  
• Map file names to table names by concatenating the 3-character APPX application ID, an underscore, and the 8-character APPX file name, then converting the result into lowercase. (Thus TAR CUSTOMER file becomes tar_customer.)
  
• Create proxy lock files in Database 'LOK'.

The FMS Control parser is very unforgiving. Syntax errors will likely result in an APPX infinite loop. This will be improved in a future release.

System Data Source (DSN):

ODBC requires a specification identifying the System Data Source, using one of the following formats:

     DSN=<data_source_name>:
     DSN=<data_source_name>; UID=<user_id>:
     DSN=<data_source_name>; UID=<user_id>; PWD=<password>:

For example, to connect to an Access data source, you would provide ODBC with a specification such as:

     DSN=Access-Accounting;: 

To connect to an MS SQL-Server Database (which requires a user name and password) you might specify:

     DSN=sql_server; UID=bobby; PWD=ybbob;: 

To connect as the SQL-Server administrator (with a blank password):

     DSN=local_sql_server; UID=sa; PWD=;:
    

Table Names (table_name):

When you define a File System Groups, you must specify 1)FMS Controls. The APPX/ODBC Connection understands the following FMS controls:

     DSN=<expression>:         - specifies ODBC Data Source
     table_name=<expression>:  - specifies ODBC table name
     proxy_db=<expression>:    - specifies proxy locking Database

Note that required colons terminate each <expression>. <expression> may use the following 'variables':

     $db      - maps to 3-character APPX Database ID
     $appl    - maps to 3-character APPX application ID
     $version - maps to 2-character APPX version
     $file    - maps to 8-character APPX file name
     $uid     - maps to 3-character APPX user id
     $pid     - maps to Unix process ID
     $uname   - maps to Unix user name
     $ucase( <expression> )  - converts <expression> to upper-case
     $lcase( <expression> )  - converts <expression> to lower-case

You can use these FMS control specifications to define a mapping algorithm for file names. For example:

     table_name = $lcase( $appl_$file ); 

... will cause us to convert APPX file names to lower-case and prepend the 3-character application ID and an underscore. (For example "TGL BALANCE1" will be converted to "tgl_balance1").

If your ODBC Data Source Name (DSN) contains multiple Databases, try opening the file from APPX. Data Sources that support multiple Databases will sometimes pop up an interactive box asking you which Database you wish to operate upon.

The current release of APPX has a very picky FMS control parser. If your FMS control specifications are not syntactically correct, APPX will hang when you try to create a data file in that File System Group. Sorry.

Row Locking (proxy_db):

Because most ODBC compliant Databases do not handle "intent" record locks, the APPX/ODBC Connection manages Row Locking external to the underlying Database.

When you read a record (row) with Hold, APPX locks (by 'intent') that record for rewrite or deletion, preventing other APPX users from locking the record.

To manage locking among multiple users, APPX uses its own 'proxy' Database. Define the following in your FMS Control specification:

     proxy_db=<3-character Database ID>:

(note the ':' is required). For example:

     proxy_db=LOK:
 

This tells APPX to use an APPX Database 'LOK' to build proxy locking files. This Database should not be the same as your operating database. It should be a name otherwise unused. 'LOK' is a good choice for a proxy database. Proxy locking files are located in directory:

     $APPXPATH/<proxy_db_id>/<application>/Data/FILE.dat
 

Field to Column Mapping:

The APPX/ODBC Connection will pick an ODBC data type for each field. APPX queries the Data Source for a list of supported data types and picks the most closely matched data type.

Some APPX data types (such as partial time/date fields) are not supported by all ODBC data sources. In this case, APPX stores those fields in a character column.

Converting to and from ODBC Data Sources:

To convert an existing AppxIO file into an ODBC Data Source, Export the file, change the file's FMS type from 1 to 6, and re-Import the file.

To convert data stored in an ODBC Data Source back into AppxIO, Export it, change its FMS type from 6 back to 1 (AppxIO), and re-Import it.

Debugging:

• Setting APPX_SQL_CMD={filename} produces an SQL Log of all SQL traffic from APPX to the RDBMS backend. It records all commands APPX sends to the RDBMS, and all data the RDBMS sends back to APPX. Set this variable to a log file location into which APPX has write permissions.

APPX_DBG_CODE=0xFFFFFFFF must also be set to enable APPX_SQL_CMD logging. Go to Setting Environment Variables for information on how to set APPX_SQL_CMD and APPX_DBG_CODE.

• Under Windows, you can also bring up the ODBC Administrator utility used originally to set up the data source. In the "Tracing" tab, click on "Start Tracing" to start and "Stop Tracing" to stop. A trace has to be started before your APPX session has ever tried to access the data file. I.E., if APPX tries to get to the data and fails, you must completely exit APPX, and go back in, to get a trace.
  
• The free WinSQL utility www.imranweb.com/freesoft.htm is a great tool for debugging connections to ODBC data sources. You can attach WinSQL to any ODBC data source and browse and run SQL commands on it. It is good at passing through error messages that our APPX/ODBC connection might filter out. Thus, it's a good debugging tool if you're unable to get APPX for Windows to talk successfully to an ODBC / SQL-Server backend to APPX.

  WinSQL has an option to execute a text file containing SQL commands. So you can point it at an edited SQL_CMD log, and see how the SQL commands APPX sends to the Data Source behave under a 'thin' SQL client. Further, you can use it to massage table creation to manually set up the SQL table, if necessary (such as to modify APPX fieldnames that the ODBC Data Source might not like).