PostgreSQL: add_column "after" option usage in Rails migration

Question

I'm trying to add a new column, 'latitude', to an existing Postgres table, after the 'location' column.

Using this syntax puts the column in the correct place:

add_column :table, :column, :decimal, :after => :existing_column

And using this syntax ensures that the field is the correct data type

add_column :table, :column, :decimal, {:precision => 10, :scale => 6}

But when I try and combine the two:

add_column :table, :column, :decimal, {:precision => 10, :scale => 6}, :after => :existing_column

I get "ArgumentError: wrong number of arguments (5 for 3..4)"

"Not to worry", I thought, "I'll just combine the arguements!":

add_column :table, :column, :decimal, {:precision => 10, :scale => 6, :after => :existing_column}

But then the columns appear at the end of the table. What am I doing wrong?

Thanks :)

Solution

Your last definition is correct. But the problem here isn't with Rails, but with PostgreSQL, which doesn't allow to add a column at specific position. Read more: How can I specify the position for a new column in PostgreSQL?