Relation constructor questions

[Lennart Jonsson]

I started playing around with Dee and have two reflections.

1. If I create a relation like:

>>> from Dee import *
>>> X = Relation(['A'],[(1)])
>>> X
Relation(('A',),
[],
{'PK':(Key, None)})

I.e. it has no body. I would have expected X to look like:

>>> X
Relation(('A'),
[Tuple(A=1)],
{'PK':(Key, None)})

Is it intended this way?

2. Do you think it would be a good idea to always store the heading in upper (or lower) case? I.e.

>>> X = Relation(['A','b'],[(1,1)])
>>> Y = Relation(['a','B'],[(1,1)])
>>> X==Y
True

I can imagine some confusion in a situation like:

>>> Student = Relation(['StudentId', 'Whatever'],[(1,'a'),(2,'b')])
>>> Mark = Relation(['Studentid','Mark'],[(1,'G')])
>>> Student & Mark
Relation(('Studentid', 'StudentId', 'Whatever', 'Mark'),
[Tuple(Studentid=1, StudentId=1, Whatever='a', Mark='G'), Tuple(Studentid=1, StudentId=2, Whatever='b', Mark='G')],
{'PK':(Key, None)})

Regards
/Lennart

[Lennart Jonsson]

Ah, yes. One has to use a tuple. Silly me :-)

>>> X = Relation(['A'],[(1,)])
>>> X
Relation(('A',),
[Tuple(A=1)],
{'PK':(Key, None)})

Perhaps it would be a good idea to throw an error in the case of:

>>> X = Relation(['A'],[(1)])
>>> X
Relation(('A',),
[],
{'PK':(Key, None)})

Regards
/Lennart

[Greg Gaughan]

1. Indeed, a tuple is needed so in Python the trailing comma in (1,) is important. I like your suggestion of raising an error if (1) is passed - I'll add it to the todo list.

2. It would help if you use a consistent way of naming the heading attributes. I tend to use Pascal case, but I don't think it's something that should be enforced or matched case-insensitively since Python is case sensitive with its names. Perhaps some kind of pre-parser, or maybe a verbose-checking-mode, to check the sanity of a schema or set of expressions would be useful. This could spot mis-spellings, and joins where the column names were probably meant to match but didn't, and unintended cartesian joins etc.