Compilation extension in SQLAlchemy: functions used in indexes

Question

I want to make a case-insensitive unique constraint in SQLAlchemy, which would work with both Postgres and SQLite.

In Postgres it is achieved:

• SQL:

Answer 1

the @compiles method has to return a string. Also, there's some glitch in how Index is traversing the functionelement here so we need one little workaround:

class CaseInsensitive(FunctionElement):
    __visit_name__ = 'notacolumn'
    name = 'CaseInsensitive'
    type = VARCHAR()


@compiles(CaseInsensitive, 'sqlite')
def case_insensitive_sqlite(element, compiler, **kw):
    arg1, = list(element.clauses)
    return compiler.process(collate(arg1, 'nocase'), **kw)


@compiles(CaseInsensitive, 'postgresql')
def case_insensitive_postgresql(element, compiler, **kw):
    arg1, = list(element.clauses)
    return compiler.process(func.lower(arg1), **kw)