Using the SQL Gateway with ODBC

Creating an ODBC SQL Gateway Connection

To define a gateway connection for an ODBC-compliant data source, perform the following steps:

1. Define an ODBC data source name (DSN) for the external database. See the documentation for the external database for information on how to do this.

2. In the Management Portal, go to the System Administration > Configuration > Connectivity > SQL Gateway Connections page.

3. Click Create New Connection.

4. On the Gateway Connection page, enter or choose values for the following fields:

   • For Type, choose ODBC.

   • Connection Name — Specify an identifier for the connection, for use within Caché.

   • Select an existing DSN — Choose the DSN that you previously created. You must use a DSN, since the ODBC SQL Gateway does not support connections without a DSN.

   • User — Specify the name for the account to serve as the default for establishing connections, if needed.

   • Password — Specify the password associated with the default account.

   For example, a typical connection might use the following values:

   Setting	Value
   Type	ODBC
   Connection Name	ConnectionODBC1
   Select an existing DSN	MyAccessPlayground
   User	DBOwner
   Password	DBPassword

   Also see “Implementation-specific Options” later in this chapter.

5. Optionally test if the values are valid. To do so, click the Test Connection button. The screen will display a message indicating whether the values you have entered in the previous step allow for a valid connection.

6. To create the named connection, click Save.

7. Click Close.

Creating an ODBC Connection to Caché via the SQL Gateway

Caché provides ODBC drivers and thus can be used as an ODBC data source. That is, a Caché instance can connect to itself or to another Caché instance via ODBC and the SQL Gateway. Specifically, the connection is from a namespace in one Caché to a namespace in the other Caché. To connect in this way, you need the same information that you need for any other external database: the connection details for the database driver that you want to use. This section provides the basic information.

Implementation-specific Options

Before you define an SQL gateway connection, you should make sure that you understand the requirements of the external database and of the database driver, because these requirements affect how you define the connection. The following options do not apply to all driver implementations.

Using the UNIX® ODBC SQL Gateway Test Program

Within a full UNIX® Caché installation, you can use a special program to test gateway access from Caché.

The gateway test program consists of files in the directory install-dir/dev/odbc/samples/sqlgateway

• gatewaytest.sh — The shell script that runs the test. This script defines the ODBCINI environment variable (so that the ODBC initialization file can be found), sets up the search path to find the driver manager, and then accesses a DSN named samples, and executes a routine. This DSN is defined in the sample ODBC initialization file and points to the Caché SAMPLES namespace.

  You may need to modify the shell script, depending on your configuration. See the section “Modifying the Shell Script for the SELECT Test” for details.

• SQLGatewayTest.ro — A routine that makes the callout to the Caché SAMPLES namespace using iODBC and the Caché ODBC client driver libcacheodbc.so.

To use the test program:

1. Go to install-dir/dev/odbc/samples/

2. Execute the test script by typing the following:

   ./sqlgateway/gatewaytest.sh
   
   

   

The gatewaytest.sh script does the following:

1. It starts a Caché session and runs the routine SQLGatewayTest in the SAMPLES namespace.

2. This application routine then loads the default Caché SQL Gateway driver, cgate.so, which is linked against the iODBC driver manager.

3. The driver manager loads the client driver using information from the ODBC initialization file.

4. The client driver then establishes a TCP/IP connection to port 1972 and is connected to the Caché SAMPLES namespace using the DSN definition from the ODBC initialization file.

5. The routine executes the following query:

   SELECT * FROM SAMPLE.PERSON
   

   

6. The routine then fetches the first ten rows of the result set.

The difference between this example and the simple select test is that in gatewaytest.sh, the Caché process making the initial call is the client application. Typically, a Gateway call from Caché calls the DSN of another vendor’s database.

Creating and Using an External Data Set

To create and use a data set that queries an external database, do the following:

1. Create an instance of %SQLGatewayConnectionOpens in a new tab via the %New method.

2. Call the Connect method of that instance, passing arguments that specify the ODBC data source name, as well as the username and password that are needed to log into that source, if necessary.

   The Connect method has the following signature:

   method Connect(dsn, usr, pwd, timeout) returns %Status
   
   

   

   Here dsn is the DSN for the data source, usr is a user who can log into that data source, pwd is the corresponding password, and timeout specifies how long to wait for a connection.

   For more information on connecting, see “Managing the Connection” in the section on Performing ODBC Programming.

3. Create an instance of %ResultSetOpens in a new tab via the %New method, providing the string argument "%DynamicQueryGW:SQLGW".

   Note:

   Notice that this is slightly different from the argument that you use with a typical dynamic query ("%DynamicQuery:SQL").

4. Invoke the Prepare method of the data set. The first argument should be a string that consists of a SQL query, the second argument should be omitted, and the third argument should be the instance of %SQLGatewayConnectionOpens in a new tab.

   This method returns a status, which should be checked.

5. Call the Execute method of the data set, optionally providing any arguments in the order expected by the query. This method returns a status, which should be checked.

To use the data set, you generally examine it one row at a time. You use methods of %ResultSetOpens in a new tab to retrieve information such as the value in a given column.

To advance to the next row, you use the Next method; typically you iterate through all the rows until you reach the end, when Next returns 0. The Next method also returns 0 if an error occurs.

An example follows:

ClassMethod SelectAndWrite() as %Status
{
    Set conn=##class(%SQLGatewayConnection).%New()
    Set sc=conn.Connect("AccessPlayground","","")
    If $$$ISERR(sc) do $System.Status.DisplayError(sc) quit

    Set res=##class(%ResultSet).%New("%DynamicQueryGW:SQLGW")
    Set sc=res.Prepare("SELECT * FROM PEOPLE",,conn)
    If $$$ISERR(sc) do $System.Status.DisplayError(sc) quit

    Set sc=res.Execute()
    If $$$ISERR(sc) do $System.Status.DisplayError(sc) quit

    While res.Next()
    { Write !,res.GetData(1)," ",res.GetData(2)," ",res.GetData(3)
    }
    Set sc=conn.Disconnect()
    Quit sc
}

For more information on %ResultSetOpens in a new tab, see the chapter “Dynamic SQL” in Using Caché SQL. Also see the class documentation for %ResultSetOpens in a new tab.

Performing ODBC Programming

If %ResultSetOpens in a new tab does not provide enough control, you can perform ODBC programming. The %SQLGatewayConnectionOpens in a new tab class provides a set of methods that correspond to ODBC functions, as well as other utility functions. With this class, you can connect to and use an ODBC-compliant database and then perform low-level ODBC programming. The overall procedure is as follows:

1. Create an instance of %SQLGatewayConnectionOpens in a new tab via the %New method.

2. Call the Connect method of that instance, passing arguments that specify the ODBC data source name, as well as the username and password that are needed to log into that source, if necessary.

   For more information on connecting, see “Managing the Connection.”

3. Call the AllocateStatement method and receive (by reference) a statement handle.

4. Call other methods of the gateway instance, using that statement handle as an argument. Most of these methods call ODBC functions.

This section discusses the following:

• Null Values and Empty Strings — differences in how Caché and SQL represent null values and empty strings.

• Checking the Status — how to check the status of your activities

• Managing the Connection — properties and methods for managing the connection to the external data source.

• Basic Methods — the basic methods that this class provides as an interface for ODBC functions.

• Getting Information about the Shared Library — how to get information about the currently loaded shared library (for the Caché ODBC SQL Gateway).

• Unloading the Shared Library — how to unload this shared library

• Other Methods — how to use some other methods of the %SQLGatewayConnectionOpens in a new tab class.

• Example — a simple example that executes a query.

Checking the Status

Most of the methods of %SQLGatewayConnectionOpens in a new tab return a status, which you should check. Status information is also available via the following properties and methods:

sqlcode property (%Integer)

Contains the SQL code return by the last call (if any).

GatewayStatus property (%Integer)

Indicates the status of the last call. This is one of the following:

• 0 - success

• -1 - SQL error

• -1000 - critical error

GetLastSQLCode() method

method GetLastSQLCode() returns %Integer

Returns an SQL code for the last call if this call does not return an SQL code (for example, if you used SQLGetData).

GatewayStatusGet() method

method GatewayStatusGet() returns %Integer

Returns an error code for the last call. It does not initialize the error code and can be called multiple times. See the previous notes for the GatewayStatus property.

Managing the Connection

The %SQLGatewayConnectionOpens in a new tab class provides properties and methods that you can use to manage the connection to the external data source.

DSN property (%String)

Data source name of the ODBC-compliant data source to which you want to connect.

User property (%String)

Username to log into the data source.

Password property (%String)

Associated password.

ConnectionHandle property (%Binary)

The current connection handle to the ODBC-compliant data source.

Connect() method

method Connect(dsn, usr, pwd, timeout) returns %Status

Establishes a connection to a DSN. If username and password are both empty, this method calls the ODBC function SQLDriverConnect. If that call is unsuccessful or username/password are specified, the method calls the ODBC function SQLConnect.

If the timeout parameter is not 0, SQLSetConnectAttr is first called to set SQL_ATTR_LOGIN_TIMEOUT.

GetConnection() method

method GetConnection(conn, timeout) returns %Status

Establishes a connection. This method uses an entry from the Caché configuration to determine the DSN, username, and password.

SetConnectOption() method

method SetConnectOption(opt, val) returns %Status

Invokes the ODBC function SQLSetConnectAttr. Only integer values are supported. Integer values for the opt argument may be taken from the sql.h and sqlext.h header files.

Disconnect() method

method Disconnect() returns %Status

Closes the connection.

Getting Information about the Shared Library

The %SQLGatewayConnectionOpens in a new tab class provides properties and methods that you can call to get information about the shared library used by the ODBC SQL Gateway.

Note:

The phrase shared library refers in general to the file or library that comprises the ODBC SQL Gateway. On Windows platforms, this is a file with the extension .dll, but the filename is different on other platforms (see “Key File Names” for a complete list of Caché SQL Gateway shared objects available for supported UNIX® platforms). The properties and methods described here apply in all cases.

DLLHandle property (%Binary)

Handle for the shared library, as currently in use. This is set when you connect.

DLLName property (%String)

Name of the shared library currently in use. This is set when you connect.

GetGTWVersion() method

method GetGTWVersion() returns %Integer

Returns the current version of the shared library.

GetUV() method

method GetUV(ByRef infoval) returns %Status

Returns (by reference) whether the shared library was built as Unicode. Note that this method always returns a status of $$$OK.

Unloading the Shared Library

The %SQLGatewayConnectionOpens in a new tab class provides a method that you can use to unload the shared library for the ODBC SQL Gateway.

UnloadDLL() method

method UnloadDLL() returns %Status

Unloads the shared library from the process memory.

Other Methods

The %SQLGatewayConnectionOpens in a new tab class provides other utility methods:

FetchRows()

method FetchRows(hstmt, Output rlist As %List, nrows As %Integer) returns %Status

Returns (by reference) a specified number of rows for the given connection handle. Here hstmt is the connection handle, returned (by reference) from AllocateStatement(). Also, rlist is the returned list of rows; this is a Caché $list. Each item in the list contains a row. If there is no data (SQL_CODE = 100), fetching is assumed to be successful but the return list is empty.

Caution:

This method is primarily useful for testing, and it truncates character fields up to 120 characters so that more fields would fit in a row. Use GetData() instead when you need non-truncated data.

GetOneRow()

method GetOneRow(hstmt, ByRef row) returns %Status

Returns (by reference) the next row for the given connection handle. Here hstmt is the connection handle, returned (by reference) from AllocateStatement(). Also, row is the returned row, a Caché $list. Each item in the list contains a field. If there is no data (SQL_CODE = 100), fetching is assumed to be successful but the return list is empty.

Caution:

This method is primarily useful for testing, and it truncates character fields up to 120 characters so that more fields would fit in a row. Use GetData() instead when you need non-truncated data.

GetParameter()

method GetParameter(hstmt, pnbr, ByRef value) returns %Status

Returns (by reference) the current value of the indicated parameter. Here hstmt is the connection handle returned (by reference) from AllocateStatement() and pnbr is the ordinal number of the parameter.

SetParameter()

method SetParameter(hstmt, pvalue, pnbr) returns %Status

Sets the value of a previously bound parameter. Here hstmt is the connection handle returned (by reference) from AllocateStatement(), pvalue is the value to use, and pnbr is the ordinal number of the parameter. The parameters are stored in $list format. If the allocated buffer is not sufficient, a new buffer will be allocated.

Example

The following shows a simple example that executes a query:

ClassMethod ExecuteQuery(mTable As %String)
{
 set mDSN="DSNtest"
 set mUsrName="SYSDBA"
 set mUsrPwd="masterkey"

 set mx=##class(%SQLGatewayConnection).%New()
 set status=mx.Connect(mDSN,mUsrName,mUsrPwd)
 if $$$ISERR(status) do $System.Status.DisplayError(status) quit $$$ERROR()
 set hstmt=""
 set status=mx.AllocateStatement(.hstmt)
 if $$$ISERR(status) do $System.Status.DisplayError(status) quit $$$ERROR()
 set status=mx.Prepare(hstmt,"SELECT * FROM "_mTable)
 if $$$ISERR(status) do $System.Status.DisplayError(status) quit $$$ERROR()
 set status=mx.Execute(hstmt)
 if $$$ISERR(status) do $System.Status.DisplayError(status) quit $$$ERROR()
 quit mx.Disconnect()
}