Rails - Jul 2008 - possible to add columns to a database table from a controller? (not from a migration)

I am trying to figure out how to add columns to a database table from
within a controller.  I have a client who wants to be able to add
their own attributes to a model from within the running application,
so I don''t think using migrations is an option.

Basically, I have a Person model which starts off with some basic
attributes (like first_name and last_name), and my client wants to be
able to add new attributes on the fly through the application (like
birthdate or hometown, or anything he can think of). My plan for
implementing this is to use another model (PersonField) to keep track
of each new attribute''s name, label, data type, and default value, and
then tie the creation, updating, or destruction of these PersonField
objects to the addition, changing, or removing of columns to the
''people'' table in the database.

To restate it in another way, I''m looking for the equivalent to
''add_column'' in a migration, but I''d like to call it
from a
controller.

I have not been able to find a solution to this problem, but I''m
relatively new to Rails (just a few months experience), so I may not
be looking in the right places.

I''d appreciate any help or suggestions anyone can give me.  Thanks for
reading this!

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You could run the execute method and pass it the query that creates the
column

I''d personally create a table to hold these attributes, and add rows to
it,
rather than creating/dropping columns dynamically.  That is I''d create
an
attribute model and give it a foreign key to the row in the other table, the
name, and the value (and possibly a column for each possible type + a type
column.)

On Wed, Jul 30, 2008 at 1:34 AM, mikebind
<mikebind-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> I am trying to figure out how to add columns to a database table from
> within a controller.  I have a client who wants to be able to add
> their own attributes to a model from within the running application,
> so I don''t think using migrations is an option.
>
> Basically, I have a Person model which starts off with some basic
> attributes (like first_name and last_name), and my client wants to be
> able to add new attributes on the fly through the application (like
> birthdate or hometown, or anything he can think of). My plan for
> implementing this is to use another model (PersonField) to keep track
> of each new attribute''s name, label, data type, and default value,
and
> then tie the creation, updating, or destruction of these PersonField
> objects to the addition, changing, or removing of columns to the
> ''people'' table in the database.
>
> To restate it in another way, I''m looking for the equivalent to
> ''add_column'' in a migration, but I''d like to
call it from a
> controller.
>
> I have not been able to find a solution to this problem, but I''m
> relatively new to Rails (just a few months experience), so I may not
> be looking in the right places.
>
> I''d appreciate any help or suggestions anyone can give me.  Thanks
for
> reading this!
>
> >
>
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On Wed, Jul 30, 2008 at 3:34 AM, mikebind
<mikebind-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> I am trying to figure out how to add columns to a database table from
> within a controller.  I have a client who wants to be able to add
> their own attributes to a model from within the running application,
> so I don''t think using migrations is an option.
>
> Basically, I have a Person model which starts off with some basic
> attributes (like first_name and last_name), and my client wants to be
> able to add new attributes on the fly through the application (like
> birthdate or hometown, or anything he can think of). My plan for
> implementing this is to use another model (PersonField) to keep track
> of each new attribute''s name, label, data type, and default value,
and
> then tie the creation, updating, or destruction of these PersonField
> objects to the addition, changing, or removing of columns to the
> ''people'' table in the database.
>
> To restate it in another way, I''m looking for the equivalent to
> ''add_column'' in a migration, but I''d like to
call it from a
> controller.
You can always execute arbitrary sql commands by using Model.find_by_sql

A better way may be to store these customs fields in the database:

Person
  has_many :person_fields

PersonField
  belongs_to :custom_field
  belongs_to :person

CustomField
  has_many :person_fields

> I have not been able to find a solution to this problem, but I''m
> relatively new to Rails (just a few months experience), so I may not
> be looking in the right places.
>
> I''d appreciate any help or suggestions anyone can give me.  Thanks
for
> reading this!
>
> >
>
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The reason there''s no easy method for doing what you want to do is
because it''s a terrible idea! Letting the customer arbitrarily change
the structure of the database is guaranteed to get you an unstable
database.

You already have a second table in mind to store data about the
arbitrary fields the customer wants to create. Have a third table that
stores the data and includes pointers back to the attribute table and
the persons table. You can set this sort of thing up easily with a
has_many :through relationship. This is much more stable and requires
no special programming. The customer can create or delete data fields
on the fly, use them inconsistently or not at all, and the data remain
easily accessible.



On Jul 30, 4:34 am, mikebind
<mikeb...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I am trying to figure out how to add columns to a database table from
> within a controller.  I have a client who wants to be able to add
> their own attributes to a model from within the running application,
> so I don''t think using migrations is an option.
>
> Basically, I have a Person model which starts off with some basic
> attributes (like first_name and last_name), and my client wants to be
> able to add new attributes on the fly through the application (like
> birthdate or hometown, or anything he can think of). My plan for
> implementing this is to use another model (PersonField) to keep track
> of each new attribute''s name, label, data type, and default value,
and
> then tie the creation, updating, or destruction of these PersonField
> objects to the addition, changing, or removing of columns to the
> ''people'' table in the database.
>
> To restate it in another way, I''m looking for the equivalent to
> ''add_column'' in a migration, but I''d like to
call it from a
> controller.
>
> I have not been able to find a solution to this problem, but I''m
> relatively new to Rails (just a few months experience), so I may not
> be looking in the right places.
>
> I''d appreciate any help or suggestions anyone can give me.  Thanks
for
> reading this!
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