Re: [sqlalchemy] Where to use and vs and_()

[Jonathan Vanasco]

On Wednesday, February 17, 2016 at 4:34:35 AM UTC-5, Simon King wrote:
>
>
> (expr1 == expr2) & (expr3 == expr4)
>

you usually won't need to & or and_ though.

filter automatically "and"s a list.

.filter(expr1 == expr2, expr3 == expr4)

the only you need to use `and_` is when doing more complicated queries and 
the "and" is nested.

.filter(or_(expr1 == expr2,
   and_(expr2 == expr3,
   expr3 == expr4
   ))

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Re: [sqlalchemy] Where to use and vs and_()

[Simon King]

On Wed, Feb 17, 2016 at 7:46 AM, Krishnakant  wrote:

> Hello all,
> The subject might have made my problem already clear.
> So I am unclear about when I should use the normal Python "and " vs the
> sqlalchemy "and_" while writing where, having or similar queries including
> joins.
> I have tryed understanding this but may be I have overlooked some thing.
> Kindly give some pointers.
> Happy hacking.
> Krishnakant.
>
>
You probably don't ever want the python keyword "and" when constructing
queries. It doesn't trigger any of SQLAlchemy's smart SQL-construction
behaviour. You might be thinking of the bitwise operator "&", which
SQLAlchemy hijacks and converts to an SQL "AND".

As far as I'm aware, "expr1 & expr2" is completely equivalent to
"and_(expr1, expr2)" if expr1 and expr2 are both SQLAlchemy expressions, so
you can use whichever you prefer.

http://docs.sqlalchemy.org/en/rel_1_0/core/sqlelement.html#sqlalchemy.sql.expression.and_

Note the warning on that page about operator precedence though; the bitwise
operators have higher precedence than the comparison operators, so this
probably wouldn't do what you expect:

expr1 == expr2 & expr3 == expr4

You'd need to write that as:

(expr1 == expr2) & (expr3 == expr4)

Simon

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[sqlalchemy] Where to use and vs and_()

[Krishnakant]

Hello all,
The subject might have made my problem already clear.
So I am unclear about when I should use the normal Python "and " vs the 
sqlalchemy "and_" while writing where, having or similar queries 
including joins.

I have tryed understanding this but may be I have overlooked some thing.
Kindly give some pointers.
Happy hacking.
Krishnakant.

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