Copyright © 2007 SoftVelocity, All rights reserved worldwide

Clarion Language

Clarion's Application Generator is so powerful that many Clarion developers write amazingly little "hand code." But because the code that the Application Generator generates is in fact Clarion language code, anyone who really wants to know about or learn how Clarion works should examine the code and learn the programming language.

Clarion allows for a rich variety of data types, including reference variables, which are similar to pointers but "safer." It provides an object oriented structure, including support for classes, as well as inheritance, encapsulation, and polymorphism.

A simple "Hello World" program can be found here. The rest of this section will concentrate on how the language handles database access. Clarion, unlike some other development environments, was designed for database access. Clarion is a data aware language, as opposed to a general purpose language with data access libraries.

The core data elements are FILE and RECORD. These are descended directly from COBOL. The FILE is a data type that describes a table. The RECORD is a data type that describes the columns in the table.

The following is a FILE declaration:

Detail           FILE,DRIVER('Scalable'),OWNER('pervas|EXAMPLE'),NAME('Detail'),PRE(DTL),BINDABLE,THREAD
KeyDetails        KEY(DTL:CustNumber,DTL:OrderNumber,DTL:LineNumber),NAME('PK_CUSTNUMBER'),NOCASE,OPT,PRIMARY
KeyProductNum     KEY(DTL:ProductNumber),DUP,NAME('1'),NOCASE,OPT
KeyCustOrderNum   KEY(DTL:CustNumber,DTL:OrderNumber),DUP,NAME('2'),NOCASE,OPT
Record             RECORD,PRE()
CustNumber          LONG
OrderNumber         LONG
LineNumber          SHORT
ProductNumber       LONG
QuantityOrdered     DECIMAL(7,2)
BackOrdered         BYTE
Price               DECIMAL(7,2)
TaxRate             DECIMAL(6,4)
TaxPaid             DECIMAL(7,2)
DiscountRate        DECIMAL(6,4)
Discount            DECIMAL(7,2)
Savings             DECIMAL(7,2)
TotalCost           DECIMAL(10,2)
                   END
                END

The FILE declaration describes a table called "Detail" on a Pervasive.SQL 2000 database server called "pervas," in a database named "Example." It describes access via one of Clarion's pluggable file drivers (called "Scalable," because we didn't update the name of the driver when the database product name was changed!). It further describes the keys and indices, including the internal names used by the database.

The RECORD is nested inside the FILE declaration. It describes the column names and datatypes. Note the prefix ("DTL"). In referencing any column, Clarion code prepends the prefix to the field name, as in DTL:CustNumber.

To establish a connection, the developer can simply use the OPEN statement, with the name of the FILE:

OPEN(Detail)

To choose a particular key or sort order, the developer can use the SET statement:

SET(DTL:KeyDetails)

To fill the record buffer with the first record, the developer can use the NEXT statement:

Next(Detail)

Or, to position the record pointer at the record for customer 1234 (the "Details" key is customer number key and contains no duplicates because it's the primary key), the developer can put the value they want to find in the record buffer, and then use the GET statement:

Detail.CustNumber = 1234
GET(Detail, KeyDetails)

With the desired record now in the buffer, if there is a control in the current window pointing to the customer number field, it will now contain the customer number for this row (this is accomplished through the USE attribute on the control, which would point to the data variable with it prefix and field name, which is DTL:CustNumber). If the end user changes the information in the control, after the ACCEPT loop (which gets the end user input), the developer can update the record (assuming that it's still the current one in the buffer) with:

PUT(Detail)

If the developer then wishes to close the connection to the database:

CLOSE(Detail)

This is a simple overview. In practice, there would be much error handling: what if the network were down and we didn't connect? What if the record for 1234 were not found? What if someone else had locked the record?

The templates generate all required error handling.

SQL Accelerators

Copyright © 2007 SoftVelocity, All rights reserved worldwide