Better error for undialected ColumnExpression

[ADBond]

If you try to use a ColumnExpression without setting a dialect you get AttributeError: 'ColumnExpression' object has no attribute 'sql_dialect'.

Maybe wrap this in a property that gives a clearer pointer to how to address this.

[browo097302]

Hi I'd be interested in helping with this. What kind of approach did you have in mind? Maybe could have an else statement from the init method to handle when sql_dialect is none with an attribute error showing more clear instructions.
Or as you mentioned wraping in a property, that handles that case?

If you have any further direction on how you would like this done I would be happy to help.

Cheers

[RobinL]

splink/splink/internals/column_expression.py

Line 50 in 4498949

if sql_dialect is not None:

I think Andy is suggesting that you use a @property for sql_dialect. This property would raise a more descriptive error when sql_dialect is None, rather than failing silently or setting it directly in the __init__ method.

A typical pattern here would be to store the dialect as self._sql_dialect in the __init__ method. In the property getter, you can check if self._sql_dialect is None, and if it is, raise a more user-friendly error indicating that the dialect needs to be set before usage. This way, you avoid relying on AttributeError and provide a clearer message on how to resolve the issue.

For example:

def __init__(self, sql_expression: str, sql_dialect: SplinkDialect = None):
    self.raw_sql_expression = sql_expression
    self.operations: list[ColumnExpressionOperation] = []
    self._sql_dialect = sql_dialect  # Store dialect as a private attribute

And for the property:

@property
def sql_dialect(self):
    if self._sql_dialect is None:
        raise ValueError("SQL dialect is not set. Please set it before using this ColumnExpression.")
    return self._sql_dialect

We'll have to see whether this approach causes any test failures, but in principle it seems like a sensible approach

[browo097302]

Yeah that makes sense, I will look into that.

[browo097302]

Ah it failed the tests, I did run tests locally and it seemed fine so I need to sort that out on my computer.

It seems to be throwing back an attributeerror: can't set attribute. Maybe it isnt handling the other class methods where sql_dialect is not set? Or perhapbs the sql dialect is not set before use.

Lmk how you think its best to tackle this.