Rails - Nov 2007 - association :conditions & instance-variable evaluation

Hello,

I was wondering if it''s possible to add :conditions to an association,
such that the conditions reference variables that need to be re-
evaluated before each query?

e.g.:
has_many :people, :conditions => "some_column @some_instance_variable,
revision_time > #{Time.now}," etc.

When I tried an example binding a date column to Time.now, the time
didn''t change with each query.  Instead, it continued using the
initial value of Time.now from when the class loaded.

Thanks,
Tom




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On 20 Nov 2007, at 00:33, tom_302 wrote:
>
> Hello,
>
> I was wondering if it''s possible to add :conditions to an
association,
> such that the conditions reference variables that need to be re-
> evaluated before each query?
>
> e.g.:
> has_many :people, :conditions => "some_column >
@some_instance_variable, revision_time > #{Time.now}," etc.
>
> When I tried an example binding a date column to Time.now, the time
> didn''t change with each query.  Instead, it continued using the
> initial value of Time.now from when the class loaded.
You can interpolate these things, but as you found

has_many :foos, :conditions => "#{xyz}"
doesn''t work: this statement is ran at class load and so the string is
interpolated

has_many :foos, :conditions => ''#{xyz}''

should do the trick.

Fred

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> has_many :foos, :conditions => ''#{xyz}''
Here'' my problem with the interpolation:

:conditions => ''allow_spatial_resampling = 
#{instance_var_that_evals_to_true}''
# => WHERE (allow_spatial_resampling = true)

Great, that works for MySQL, but not, say, SQLite. I need to do:

:conditions => [''allow_spatial_resampling = ?'', 
instance_var_that_evals_to_true]
# => MySQL: WHERE (allow_spatial_resampling = 1)
# => SQLite: WHERE (allow_spatial_resampling = ''t'')

How can I have a DB agnostic solution, where obviously the latter won''t
work at the class level.
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> How can I have a DB agnostic solution, where obviously the latter
won''t
> work at the class level.
At least for my example, I found the solution:

  :conditions => ''allow_spatial_resampling = 
#{quote_value(instance_var)}''

That works as expected, hope this helps someone out there.
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