How do I retroactively add a primary key to my table in rails?

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眼角桃花
眼角桃花 2021-02-06 22:07

I\'ve created a table without a primary key (:id => false), but now it has come back to bite my ass.

My app is already in production and I can\'t just drop it and recre

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  • 2021-02-06 23:08

    The command to add a primary key in a migration is:

    add_column :my_table, :id, :primary_key

    However, the wording of your question suggests that your table already has an auto-increment column. Unless I'm mistaken, there are several DBMS that do not allow more than one auto-increment column on a table.

    If you DO already have an auto-increment column and you actually want to use that column as your primary key, just add the following to your model:

    set_primary_key "my_existing_column"

    Or in more recent versions of Rails:

    self.primary_key = "my_existing_column"

    In the case that you already have an auto-increment column and you can't use that as the primary key, you may be out of luck.

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  • 2021-02-06 23:08

    I know in mySQl that you can add a column that has a default increment value. If you add that then each row will have a unique int value (and any new row will get a int value 1 greater then the last row added)

    You could add this column and set it as a primary key.

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  • 2021-02-06 23:09

    If for some reason you created a table with a custom id field, but forgot to set id as the primary key, you need to run a migration to create the primary key constraint. The following was tested against a PostgreSQL database:

    class AddPrimaryKeyConstraintToFoobars < ActiveRecord::Migration
      def up
        execute "ALTER TABLE foobars ADD PRIMARY KEY (id);"
      end
    
      def down
        execute "ALTER TABLE foobars DROP CONSTRAINT foobars_pkey;"
      end
    end
    
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  • 2021-02-06 23:11

    Was this a join table that now needs to become a real model with a primary key? If so, your best bet is to create the new table and copy the data into it.

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