Work with Azure Data Lake Storage Data in FoxPro

The CData ODBC driver for Azure Data Lake Storage enables you to access Azure Data Lake Storage data using the ODBC standard. You can use the CData ODBC Driver for Azure Data Lake Storage to integrate Azure Data Lake Storage data into your FoxPro project. The procedure below provides a walk-through of the included code sample, which saves Azure Data Lake Storage data into tables in a FoxPro database.

Connect to Azure Data Lake Storage as an ODBC Data Source

If you have not already, first specify connection properties in an ODBC DSN (data source name). This is the last step of the driver installation. You can use the Microsoft ODBC Data Source Administrator to create and configure ODBC DSNs.

NOTE: Set the 'Map To WVarchar' connection property to FALSE (FoxPro uses the ODBC W API and returns the WCHAR for the value type).

Authenticating to a Gen 1 DataLakeStore Account

Gen 1 uses OAuth 2.0 in Entra ID (formerly Azure AD) for authentication.

For this, an Active Directory web application is required. You can create one as follows:

1. Sign in to your Azure Account through the
2. Select "Entra ID" (formerly Azure AD).
3. Select "App registrations".
4. Select "New application registration".
5. Provide a name and URL for the application. Select Web app for the type of application you want to create.
6. Select "Required permissions" and change the required permissions for this app. At a minimum, "Azure Data Lake" and "Windows Azure Service Management API" are required.
7. Select "Key" and generate a new key. Add a description, a duration, and take note of the generated key. You won't be able to see it again.

To authenticate against a Gen 1 DataLakeStore account, the following properties are required:

• Schema: Set this to ADLSGen1.
• Account: Set this to the name of the account.
• OAuthClientId: Set this to the application Id of the app you created.
• OAuthClientSecret: Set this to the key generated for the app you created.
• TenantId: Set this to the tenant Id. See the property for more information on how to acquire this.
• Directory: Set this to the path which will be used to store the replicated file. If not specified, the root directory will be used.

Authenticating to a Gen 2 DataLakeStore Account

To authenticate against a Gen 2 DataLakeStore account, the following properties are required:

• Schema: Set this to ADLSGen2.
• Account: Set this to the name of the account.
• FileSystem: Set this to the file system which will be used for this account.
• AccessKey: Set this to the access key which will be used to authenticate the calls to the API. See the property for more information on how to acquire this.
• Directory: Set this to the path which will be used to store the replicated file. If not specified, the root directory will be used.

Connect and Transfer

To get started, add the code sample to a new project. You can execute the following command to save all tables without displaying them:

DO C:\Temp\sqldump.prg WITH "CData ADLS Source", "TESTDB", .f.

Below is the process that the program follows:

1. Create a new FoxPro database.

2. Open a connection to Azure Data Lake Storage data with the line below:

   m.hSQLconnection = SQLCONNECT(m.cODBCDSN)
   

3. If the connection was successful, you can now retrieve the list of tables using the SQLTABLES function. The code below saves the list of tables in sys_tables.dbf:

   WAIT WINDOW "Fetching tables for data source '" + m.cODBCDSN + "'..." NOWAIT NOCLEAR
   m.nSQLTABLES = SQLTABLES(m.hSQLconnection)
   
   IF lUseDistinctConnections
    WAIT WINDOW "Closing ODBC Connection for data source '" + m.cODBCDSN + "'..." NOWAIT NOCLEAR
    SQLDISCONNECT(m.hSQLconnection)
    m.hSQLconnection = 0 * SQLCONNECT needs to be called again
   ENDIF
   
   IF m.nSQLTABLES > 0
    * create local table containing list of tables in db
    COPY TO (m.cImportData + "sys_tables")
    USE
   
    * convert each table to DBF
    USE (m.cImportData + "sys_tables")
    ALTER TABLE DBF("sys_tables") ;
    ADD COLUMN records i ;
    ADD COLUMN dbfname m
   

4. Scan over each table, saving it to a DBF file. The function ODBCtoDBF stores the table in a DBF file and then opens a grid if the lBrowse parameter is set to true:

   FUNCTION ODBCtoDBF (cTableName as String, cTableType as String, lBrowse as Logical, lhSQLConnection as Integer)
   
    WAIT WINDOW ;
    "Converting " + m.cTableType + ' "' + m.cTableName + '" to DBF...' ;
    NOWAIT NOCLEAR
   
    ACTIVATE SCREEN
   
    * strip characters incompatible with FoxPro out of the name of the DBF file
    m.cTableAlias		= ""
    m.nTableNameLen		= LEN(m.cTableName)
    m.nTableNameStart	= 1
    
    FOR m.nTableNameStart = 1 TO m.nTableNameLen
    m.cCharacter = SUBSTR(m.cTableName, m.nTableNameStart, 1)	
    IF !ISALPHA(m.cCharacter) .and. (m.nTableNameStart = 1 .or. !ISDIGIT(m.cCharacter))
    m.cTableAlias = m.cTableAlias + "_"
    ELSE
    m.cTableAlias = m.cTableAlias + m.cCharacter
    ENDIF
    ENDFOR
   
    m.cFromTable = m.cTableName
    m.cTempViewAlias	= m.cTableType + "_" + m.cTableAlias
   
    LOCAL loException as Exception
    LOCAL lnResultSets
    
    TRY
    * run query
    m.lnResultSets = SQLEXEC(m.lhSQLConnection, ;
    "SELECT * FROM " + m.cFromTable, ;
    m.cTempViewAlias, ;
    aSQLResult)
   	 
    IF m.lnResultSets#1
    SET STEP ON
    ENDIF
   	
    ACTIVATE SCREEN
   
    CATCH TO m.loException
    ACTIVATE SCREEN
    ? "Error opening " + m.cTempViewAlias + ":"
    ? m.loException.Message
    ? m.loException.Details
    ENDTRY
   
    IF !USED(m.cTempViewAlias)
    RETURN
    ENDIF
   
    * copy records from view cursor to disk
    SELECT * FROM (m.cTempViewAlias) ;
    INTO TABLE (m.cImportData + m.cTableAlias)
   
    IF USED(m.cTableAlias)
   
    ACTIVATE SCREEN
   
    FLUSH	&& flush the buffer to write the data to disk
   
    IF m.lBrowse
    * pop the table up on screen
    SELECT (m.cTableAlias)
    BROWSE NORMAL NOMODIFY NOWAIT
    ACTIVATE SCREEN
    ELSE
    * close on-disk table for now
    USE IN (m.cTableAlias)
    ACTIVATE SCREEN
    ENDIF
    ENDIF
   
    IF USED(m.cTempViewAlias)
    USE IN &cTempViewAlias && close SQL view
    ACTIVATE SCREEN
    ENDIF
   
    WAIT CLEAR
   
   ENDFUNC
   

5. You can now save tables of Azure Data Lake Storage data as DBF files.

Below is the full code, in FoxPro 9 syntax:

PARAMETERS cODBCDSN, cDatabaseName, lBrowseAfterConvert

*	cODBCDSN				The ODBC data source name, used for the name of the folder where the DBF tables are stored.
*	cDatabaseName			The name of the FoxPro database to use. This database is created if it does not exist. The default is DATABASE_NAME.
*								
*	lBrowseAfterConvert		If ".t." display each table with the BROWSE command after importing it. If ".f." close each table before moving on to the next one.

#define		ODBC_DATASOURCE		"DataSourceName"
#define		DATABASE_NAME		"odbcdata"

m.m_tpath = ".\" && root directory for data

ON ERROR
SET SAFETY OFF

IF VARTYPE(m.cODBCDSN)#"C" .or. EMPTY(m.cODBCDSN)
 m.cODBCDSN = ODBC_DATASOURCE
ENDIF
IF VARTYPE(m.cDatabaseName)#"C" .or. EMPTY(m.cDatabaseName)
 m.cDatabaseName = DATABASE_NAME
ENDIF

m.cImportData = m.cODBCDSN + "\"

CLOSE TABLES ALL
CLOSE DATABASES ALL

IF !DIRECTORY(m.cImportData)
	MKDIR (m.cImportData)
ENDIF

CREATE DATABASE (m.cDatabaseName)
CREATE CONNECTION (m.cDatabaseName) DATASOURCE (m.cODBCDSN) DATABASE (m.cDatabaseName)

WAIT WINDOW "Opening ODBC Connection for data source '" + m.cODBCDSN + "'..." NOWAIT NOCLEAR
m.hSQLconnection = SQLCONNECT(m.cODBCDSN)

IF m.hSQLconnection > 0
 * Connection successful; get list of tables
 WAIT WINDOW "Fetching tables for data source '" + m.cODBCDSN + "'..." NOWAIT NOCLEAR
 m.nSQLTABLES = SQLTABLES(m.hSQLconnection)

 IF m.nSQLTABLES > 0
 * Create local table containing list of tables in db
 COPY TO (m.cImportData + "sys_tables")
 USE

 * Convert each table to DBF
 USE (m.cImportData + "sys_tables")
 ALTER TABLE DBF("sys_tables") ;
 ADD COLUMN records	i ;
 ADD COLUMN dbfname	m

 SCAN	
 m.cCurrentTable	= TRIM(sys_tables.table_name)
 m.cCurrentTableType	= TRIM(sys_tables.table_type) && Valid values are "SYSTEMTABLE", "TABLE", and "VIEW".
 IF m.cCurrentTableType = "TABLE" or m.cCurrentTableType = "VIEW"

 ODBCtoDBF(m.cCurrentTable, m.cCurrentTableType, m.lBrowseAfterConvert, m.hSQLConnection)
 ELSE
 ACTIVATE SCREEN
 ? "ERROR:", m.cCurrentTable, "Couldn't open ODBC connection."
 =MESSAGEBOX("couldn't open data source " + m.cODBCDSN + " for table " + m.cCurrentTable + ".")
 ENDIF

 ENDSCAN
 BROWSE NORMAL NOWAIT

 ELSE
 =MESSAGEBOX("No tables found in data source " + m.cODBCDSN + ".")
 SET STEP ON
 ENDIF
 
 SQLDISCONNECT(m.hSQLconnection)
 
ELSE
 =MESSAGEBOX("Could not open data source " + m.cODBCDSN + ".")
 SET STEP ON
ENDIF

FUNCTION ODBCtoDBF (cTableName as String, cTableType as String, lBrowse as Logical, lhSQLConnection as Integer)

 WAIT WINDOW ;
 "Converting " + m.cTableType + ' "' + m.cTableName + '" to DBF...' ;
 NOWAIT NOCLEAR

 ACTIVATE SCREEN

 * Strip characters incompatible with FoxPro out of the name of the DBF file
 m.cTableAlias		= ""
 m.nTableNameLen		= LEN(m.cTableName)
 m.nTableNameStart	= 1
 
 FOR m.nTableNameStart = 1 TO m.nTableNameLen
 m.cCharacter = SUBSTR(m.cTableName, m.nTableNameStart, 1)	
 IF !ISALPHA(m.cCharacter) .and. (m.nTableNameStart = 1 .or. !ISDIGIT(m.cCharacter))
 m.cTableAlias = m.cTableAlias + "_"
 ELSE
 m.cTableAlias = m.cTableAlias + m.cCharacter
 ENDIF
 ENDFOR

 m.cFromTable = m.cTableName
 m.cTempViewAlias	= m.cTableType + "_" + m.cTableAlias

 LOCAL loException as Exception
 LOCAL lnResultSets
 
 TRY
 * Run query
 m.lnResultSets = SQLEXEC(m.lhSQLConnection, ;
 "SELECT * FROM " + m.cFromTable, ;
 m.cTempViewAlias, ;
 aSQLResult)
	 
 IF m.lnResultSets#1
 SET STEP ON
 ENDIF
	
 ACTIVATE SCREEN

 CATCH TO m.loException
 ACTIVATE SCREEN
 ? "Error opening " + m.cTempViewAlias + ":"
 ? m.loException.Message
 ? m.loException.Details
 ENDTRY

 IF !USED(m.cTempViewAlias)
 RETURN
 ENDIF

 * Copy records from view cursor to disk
 SELECT * FROM (m.cTempViewAlias) ;
 INTO TABLE (m.cImportData + m.cTableAlias)

 IF USED(m.cTableAlias)

 ACTIVATE SCREEN

 FLUSH	&& Flush the buffer to write the data to disk

 IF m.lBrowse
 * Display the table on screen
 SELECT (m.cTableAlias)
 BROWSE NORMAL NOMODIFY NOWAIT
 ACTIVATE SCREEN
 ELSE
 * Close on-disk table
 USE IN (m.cTableAlias)
 ACTIVATE SCREEN
 ENDIF
 ENDIF

 IF USED(m.cTempViewAlias)
 USE IN &cTempViewAlias && Close SQL view
 ACTIVATE SCREEN
 ENDIF

 WAIT CLEAR

ENDFUNC