Case condition

PostgreSQL supports case command. The case command can be written as an ordinary python function which is later automatically transformed into SQL case. Because case is just a general if..elif..else command, there is one requirement: in the function every if <sql_condition> must contain a return. The macrotranslate module currently does not support exceptions, do not use any try:except block inside the case function.

from sqlabstr import Case
foo = db.foo()
def casefunc():
   if today() < tommorrow():  # - this is not <sql_condition>
        do_something
   if foo.age > 25:  # this is SQL condition
       if foo.city == 'alabama':
             return 'blue'
       return 'yellow
   return None
foo.AddCol(Case(casefunc) >> 'color')

## This function is incorrect!!!
def casefunc():
    if foo.x > foo.y:
        if foo.x > 5:
            return foo.x
        #### -> The (foo.x > foo.y) condition exits here without return
    if foo.z > 5:
        return 1
    return None      

The Case class acts as a macro preprocessor. Every if statement, that has as an argument general SQL condition is automatically translated into an appropriate case SQL command. The python function is evaluated before the SQL command execution, or before the output of the repr function.

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