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comp.lang.ruby

Storing a Hash in a database table using YAML--anything better?

J. B. Rainsberger

10/19/2006 11:52:00 PM

I'm a beginning Rails programmer, so please be gentle.

I want to store a hash as a single row in a database table. I'm
currently storing each name/value pair as a row with a reference back to
the "parent" row, but that seems unnecessarily complex. I want to know
whether you have any better suggestions than what I plan to try to do.

I plan to write the hash into the row in a single column by YAMLing it.
I would, of course, unYAML on read operations.

I do not plan ever to need to run a query on a single key in this hash,
so I feel comfortable storing it blob-like this way. I just wanted to
know whether anyone knows of a better way than YAML formatting/parsing
in my Rails model object.

Thanks for your help!
--
J. B. (Joe) Rainsberger :: http://www....
Your guide to software craftsmanship
JUnit Recipes: Practical Methods for Programmer Testing
2005 Gordon Pask Award for contribution Agile Software Practice
4 Answers

Gregory Seidman

10/20/2006 1:18:00 AM

0

On Fri, Oct 20, 2006 at 08:51:47AM +0900, J. B. Rainsberger wrote:
} I'm a beginning Rails programmer, so please be gentle.
}
} I want to store a hash as a single row in a database table. I'm
} currently storing each name/value pair as a row with a reference back to
} the "parent" row, but that seems unnecessarily complex. I want to know
} whether you have any better suggestions than what I plan to try to do.
}
} I plan to write the hash into the row in a single column by YAMLing it.
} I would, of course, unYAML on read operations.
}
} I do not plan ever to need to run a query on a single key in this hash,
} so I feel comfortable storing it blob-like this way. I just wanted to
} know whether anyone knows of a better way than YAML formatting/parsing
} in my Rails model object.

Look at ActiveRecord::Base.serialize. It lets you declare a column (make
sure it's a TEXT column) to be a serialized Ruby object. You can store your
hash automatically. You may also be interested in this example use of it:
http://redcorundum.blogspot.com/2006/07/ror-additional-attributes-wit...

} Thanks for your help!
} J. B. (Joe) Rainsberger :: http://www....
--Greg

J. B. Rainsberger

10/20/2006 4:24:00 AM

0

Gregory Seidman wrote:
> On Fri, Oct 20, 2006 at 08:51:47AM +0900, J. B. Rainsberger wrote:
> } I'm a beginning Rails programmer, so please be gentle.
> }
> } I want to store a hash as a single row in a database table. I'm
> } currently storing each name/value pair as a row with a reference back to
> } the "parent" row, but that seems unnecessarily complex. I want to know
> } whether you have any better suggestions than what I plan to try to do.
> }
> } I plan to write the hash into the row in a single column by YAMLing it.
> } I would, of course, unYAML on read operations.
> }
> } I do not plan ever to need to run a query on a single key in this hash,
> } so I feel comfortable storing it blob-like this way. I just wanted to
> } know whether anyone knows of a better way than YAML formatting/parsing
> } in my Rails model object.
>
> Look at ActiveRecord::Base.serialize. It lets you declare a column (make
> sure it's a TEXT column) to be a serialized Ruby object. You can store your
> hash automatically. You may also be interested in this example use of it:
> http://redcorundum.blogspot.com/2006/07/ror-additional-attributes-wit...

This is exactly the kind of thing I was hoping to see. Thank you, Greg!
I'll let you know how it goes.
--
J. B. (Joe) Rainsberger :: http://www....
Your guide to software craftsmanship
JUnit Recipes: Practical Methods for Programmer Testing
2005 Gordon Pask Award for contribution Agile Software Practice

David Vallner

10/20/2006 10:10:00 AM

0

J. B. Rainsberger wrote:
> I want to store a hash as a single row in a database table. I'm
> currently storing each name/value pair as a row with a reference back to
> the "parent" row, but that seems unnecessarily complex. I want to know
> whether you have any better suggestions than what I plan to try to do.
>

Disclaimer: A lot of the following will be database access performance
related. In personal code with low usage, those can be safely ignored,
but for a self-education project, I prefer following good practices to
learn them even if they seem clunky.

What's the structure of the hash? If it could be replaced by a data
structure, I'd do so and keep this approach (it IS the correct one from
the relational data modelling point of view), unless you're sure the
hash is an atomic value object by design.

I'd especially not use the serialization approach if you need to filter
your data according to the contents of that hash - the "draw all records
from the DB and filter them in Ruby" approach makes baby DBA Jesus cry
and is a good candidate for becoming a bottleneck. I'd also not use the
serialization approach if it's binary serialisation - if you ever had to
access the database from anything except Rails (e.g. Crystal Reports),
you're screwed.

David Vallner

Bil Kleb

10/22/2006 10:41:00 PM

0

J. B. Rainsberger wrote:
> I'm a beginning Rails programmer, so please be gentle.

Hi JB! Welcome.

Regards,
--
Bil Kleb
http://fun3d.lar...