EXTENDING LEGACY DATABASE ENGINES WITH OBJECT-BASED FUNCTIONALITY
Legacy database engines may be extended through the use of callback extension handlers on the client. For example, regular expression matching and arbitrary user-functions may be implemented in a legacy database engine without replacing the engine. A pattern string may be provided to the legacy database engine by a client with a pattern matching prefix. When the legacy database engine encounters the prefix, the database engine executes a callback to the client with a value from the database for pattern matching. The client performs the pattern matching through, for example, regular expressions, and returns a match status to the database engine. The process may be repeated for several rows of a table in the database and a dataset compiled by the database engine and returned to the client.
1 . A method, comprising:
receiving a first pattern string for a first column of a table of a database;
identifying a pattern match extension prefix in the first pattern string; and
when the pattern match extension prefix is located in the first pattern string:
calling a first extension callback function with an index pointer and a column value pointer; and
receiving a match status from the extension callback function.
2 . The method of claim 1 , in which when the pattern match extension prefix is not located in the first pattern string performing normal legacy pattern matching.
3 . The method of claim 1 , in which the index pointer specifies a particular extension callback function and in which the column value pointer is a pointer to a memory location storing data from the first column of the table for at least one row.
4 . The method of claim 1 , in which the receiving step, the identifying step, and the calling step are repeated for several rows in the table.
5 . The method of claim 4 , further comprising returning the rows of the table for which a positive match status is received from the first extension callback function.
6 . The method of claim 1 , in which the first pattern string is received from a client and in which the first extension callback function is located on the client.
7 . The method of claim 1 , in which the database is stored on a database server executing a legacy database engine.
8 . The method of claim 1 , in which identifying the pattern match extension prefix comprises identifying a hexadecimal FF value.
9 . The method of claim 1 , further comprising:
receiving a second pattern string for a second column of the table;
identifying the pattern match extension prefix in the second pattern string; and
when the pattern match extension prefix is located in the second pattern string:
calling a second extension callback function with a second index pointer and a second column value pointer; and
receiving a second match status from the second extension callback function.
10 . A computer program product, comprising:
a computer-readable medium comprising:
code to receive a pattern string for a column of a table of a database;
code to identify a pattern match extension prefix in the pattern string; and
code to, when the pattern match extension prefix is located in the pattern string, call an extension callback function with an index pointer and a column value pointer; and
code to, when the pattern match extension prefix is located in the pattern string, receive a match status from the extension callback function.
11 . The computer program product of claim 10 , in which the medium further comprises code to, when the pattern match extension prefix is not located in the pattern string, perform normal legacy pattern matching.
12 . The computer program product of claim 10 , in which the medium further comprises code to repeat the code to receive, the code to identify, and the code to call for several rows in the table.
13 . The computer program product of claim 10 , in which the medium further comprises code to return the rows of the table for which a positive match status is received from the extension callback function.
14 . The computer program product of claim 10 , in which the medium further comprises code to access a legacy database engine.
15 . The computer program product of claim 10 , in which the code to receive a pattern string receives a pattern string from a client.
16 . The computer program product of claim 15 , in which the code to call the extension callback function calls the extension callback function located on the client.
17 . A method, comprising:
receiving a callback from a database engine having an index pointer and a column value pointer;
calling an extension handler corresponding to the index pointer with the column value pointer; and
returning a match status to the database engine.
18 . The method of claim 17 , further comprising locating the corresponding extension handler for the callback by accessing a row of a callback table corresponding to the index pointer.
19 . The method of claim 17 , in which the extension handler is at least one of a regular expression object and a function object.
20 . The method of claim 17 , in which the database engine is legacy database engine.