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psqlHelp.h

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    • Bruce Momjian's avatar
      9394d62c
      I have been working with user defined types and user defined c · 9394d62c
      Bruce Momjian authored
      functions.  One problem that I have encountered with the function
      manager is that it does not allow the user to define type conversion
      functions that convert between user types. For instance if mytype1,
      mytype2, and mytype3 are three Postgresql user types, and if I wish to
      define Postgresql conversion functions like
      
      I run into problems, because the Postgresql dynamic loader would look
      for a single link symbol, mytype3, for both pieces of object code.  If
      I just change the name of one of the Postgresql functions (to make the
      symbols distinct), the automatic type conversion that Postgresql uses,
      for example, when matching operators to arguments no longer finds the
      type conversion function.
      
      The solution that I propose, and have implemented in the attatched
      patch extends the CREATE FUNCTION syntax as follows. In the first case
      above I use the link symbol mytype2_to_mytype3 for the link object
      that implements the first conversion function, and define the
      Postgresql operator with the following syntax
      
      The patch includes changes to the parser to include the altered
      syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
      changes to commands/define.c to handle the extra information in the AS
      clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
      dynamic loader figures out what link symbol to use.  I store the
      string for the link symbol in the prosrc text attribute of the pg_proc
      table which is currently unused in rows that reference dynamically
      loaded
      functions.
      
      
      Bernie Frankpitt
      9394d62c
      History
      I have been working with user defined types and user defined c
      Bruce Momjian authored
      functions.  One problem that I have encountered with the function
      manager is that it does not allow the user to define type conversion
      functions that convert between user types. For instance if mytype1,
      mytype2, and mytype3 are three Postgresql user types, and if I wish to
      define Postgresql conversion functions like
      
      I run into problems, because the Postgresql dynamic loader would look
      for a single link symbol, mytype3, for both pieces of object code.  If
      I just change the name of one of the Postgresql functions (to make the
      symbols distinct), the automatic type conversion that Postgresql uses,
      for example, when matching operators to arguments no longer finds the
      type conversion function.
      
      The solution that I propose, and have implemented in the attatched
      patch extends the CREATE FUNCTION syntax as follows. In the first case
      above I use the link symbol mytype2_to_mytype3 for the link object
      that implements the first conversion function, and define the
      Postgresql operator with the following syntax
      
      The patch includes changes to the parser to include the altered
      syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
      changes to commands/define.c to handle the extra information in the AS
      clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
      dynamic loader figures out what link symbol to use.  I store the
      string for the link symbol in the prosrc text attribute of the pg_proc
      table which is currently unused in rows that reference dynamically
      loaded
      functions.
      
      
      Bernie Frankpitt