Foreign key column name incorrect about beam

[tathougies]

@karls
I believe this is expected behavior. If you want to rename the foreign key column name, you can use the method described here to rename the primary key column.

To be clear, the default naming rules for foreign key columns is to take the name of the foreign key record name (customer_id in your case) and appending a __ and the default name of the column in the related table (id in this case).

If you have any other questions (including suggestions on better defaults), feel free to comment on the mailing list

[karls]

Hey, thanks for the clarification and the suggestion! I tried to modify the foreign key field name, but it does not seem to be possible? According to https://github.com/tathougies/beam/blob/master/beam-core/Database/Beam/Schema/Tables.hs#L132 field modifications only work on Columnar-s?

[tathougies]

Indeed, you can only rename a Columnar, but an embedded primary key is composed of columnars.

In the Chinook schema, we rename all the columns, including foreign keys embedded in other tables. We use the IsString instance of FieldModification.

So basically (making it very explicit) if you have

data CustomerT f
  = Customer
  { customerId        :: Columnar f Int32
  , customerFirstName :: Columnar f Text
  , customerLastName  :: Columnar f Text
...
  } deriving Generic
instance Beamable CustomerT
type Customer = CustomerT Identity; deriving instance Show Customer

instance Table CustomerT where
  data PrimaryKey CustomerT f = CustomerId (Columnar f Int32)


data InvoiceT f
  = Invoice
  { invoiceId       :: Columnar f Int32
  , invoiceCustomer :: PrimaryKey CustomerT f
...
  } deriving Generic

Then you can do

  defaultDbSettings `withDbModification`
  (dbModification
   { ...
   , invoice = modifyTable (\_ -> "Invoice")
                   (tableModification { invoiceCustomer = CustomerId (fieldNamed "CustomerId") })
    })

[karls]

Oh! Thanks for spelling this out for me — I got my example working as well now.

There is a fair number of types jiggle around and learn how they all fit together, but I'm hopeful. I will continue to evaluate beam for our project. :-)

Btw, appending pattern of appending __id — I hadn't come across it before.

[tathougies]

Awesome! Feel free to ask any more questions on the discussion list.

Btw, appending pattern of appending __id — I hadn't come across it before.

Just an easy way of generating unique column names 😄

[wraithm]

@tathougies This should definitely be documented better. It took me a second to figure out what's going on with foreign key field names.