Declaring an External Filter to the Database

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To declare an external filter to a database, use the DECLARE FILTER statement. For example, the following statement declares the filter, SAMPLE:

ENTRY_POINT 'FilterFunction'
MODULE_NAME 'filter.dll';

In the example, the input sub-type of the filter is defined as -1 and its output sub-type as -2. In this example, INPUT_TYPE specifies lowercase text and ­OUTPUT_TYPE specifies uppercase text. The purpose of filter, SAMPLE, therefore, is to translate Blob data from lowercase text to uppercase text.

The ENTRY_POINT and MODULE_NAME parameters specify the external routine that InterBase calls when the filter is invoked. The MODULE_NAME parameter specifies filter.dll, the dynamic link library containing the executable code of the filter. The ENTRY_POINT parameter specifies the entry point into the DLL. The example shows only a simple file name. It is good practice to specify a fully-qualified path name, since users of your application need to load the file.