I need to change the type of a column (wasserstand) from string to
integer, which already contains text.
My idea is to copy the string into a new scratch column, modify the
column type to integer and then manually set the appropriate ints.
After this, I want to remove the scratch string column in the next
migration.
The first migration should be done like this:
def self.up
tz = Teilzaehlung.all
ws = []
tz.each do |b|
ws << [b.id, b.wasserstand]
end
change_column(:teilzaehlungs, :wasserstand, :integer)
add_column(:teilzaehlungs, :wst, :string)
ws.each do |b|
beob = Teilzaehlung.find(b[0])
beob.update_attribute(:wasserstand, 0)
beob.update_attribute(:wst, b[1])
end
end
Interestingly, after running the migration, the new interger typed
column contains 0, but the scratch column wst is always NULL - even if
b[1] contains a string.
Why?
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