Agfdhyk

I am trying to create Rails models for some pre-existing database tables.

There is 1 MainTable, which has 1 ChildTable.

The problem could be the 'foreign keys' are named differently on each table

  class MainTable < ActiveRecord::Base

    has_many :child_tables, :class_name => 'ChildTable', :foreign_key => "child_column_name"

    accepts_nested_attributes_for :child_tables

    self.primary_key = "main_table_column_name"

    self.table_name = 'main_table'

  end





  class ChildTable < ActiveRecord::Base

        belongs_to :main_table, :class_name => 'MainTable', foreign_key: "child_column_name", :primary_key => "main_table_column_name"

        self.table_name = 'child_table' 

        self.primary_key = "child_table_column_name"



      end

Given that the main table will only every have 1 record per child table, but there could be many child records per main table - do these associations look correct?

I want to be able to do something like:

m = MainTable.new

m.some_value = "123"

m.mntbl_key ="999"

c = ChildTable.new

c.something = "Foo"

m.child_tables << c



m.save!

EDIT: I am no longer getting an error as I have updated the code above. It works now BUT I have to assign the ids on both tables.
If I assign the id on the Master object, it will not automatically give the child object that id in the fk column
i.e.

m = MasterTable.new

m.master_table_column_name = 99

c = ChildTable.new

m.child_tables << c

m.save!



-- This will Insert ok into Master but will INSERT a blank row into the child

However:

m = MasterTable.new

m.master_table_column_name = 99

c = ChildTable.new

c.child_column_name = 99

m.child_tables << c

m.save!



--This works and inserts correctly into both tables

--------------------------------- OLD:
But I am getting the error:

ActiveModel::MissingAttributeError: can't write unknown attribute `ctbl_key'

Am I missing something?

A one-to-many association only uses one foreign key column - not two.

Typically in rails its setup as so:

class Parent 

  has_many :children

end



class Child

  belongs_to :parent

end

The actual association is stored in the children.parent_id column.

So lets say we have an non-conventional foreign key:

class Parent 

  has_many :children, foreign_key: 'padre_id'

end



class Child

  belongs_to :parent, foreign_key: 'padre_id'

end

Easy enough. We just have to tell the associations on both side what the foreign key is. Note that the class_name option is not needed as long as the class name can be deduced from the name of the association.

Custom primary keys or table names are not a problem either as ActiveRecord looks at the model class definitions when resolving associations.

class Parent 

  self.primary_key = :custom_pk

  has_many :children, foreign_key: 'padre_id'

end



class Child

  self.table_name = 'bar'

  # this will correctly reference parents.foo

  belongs_to :parent, foreign_key: 'padre_id'

end

There is also the universal issue that you must save a record before you can add children to it:

irb(main):024:0> m = MainTable.new

=> #<MainTable custom_pk: nil, created_at: nil, updated_at: nil>

irb(main):025:0> m.child_tables.new

=> #<ChildTable id: nil, padre_id: nil, created_at: nil, updated_at: nil>

irb(main):026:0> m.save!

   (0.3ms)  BEGIN

   (0.4ms)  ROLLBACK

ActiveRecord::RecordInvalid: Validation failed: Child tables is invalid

    from (irb):26

Starting in Rails 5 belongs_to associations are non-optional by default. So the child_tables instance is not valid since the padre_id is nil.

You either need to save the parent record first:

irb(main):033:0> m = MainTable.create!

   (0.5ms)  BEGIN

  MainTable Create (0.7ms)  INSERT INTO "main_table" ("created_at", "updated_at") VALUES ($1, $2) RETURNING "custom_pk"  [["created_at", "2018-11-20 17:31:09.545476"], ["updated_at", "2018-11-20 17:31:09.545476"]]

   (0.8ms)  COMMIT

=> #<MainTable custom_pk: 5, created_at: "2018-11-20 17:31:09", updated_at: "2018-11-20 17:31:09">

irb(main):034:0> m.child_tables.new

=> #<ChildTable id: nil, padre_id: 5, created_at: nil, updated_at: nil>

irb(main):035:0> m.save

   (0.3ms)  BEGIN

  MainTable Load (0.6ms)  SELECT  "main_table".* FROM "main_table" WHERE "main_table"."custom_pk" = $1 LIMIT $2  [["custom_pk", 5], ["LIMIT", 1]]

  ChildTable Create (0.9ms)  INSERT INTO "child_table" ("padre_id", "created_at", "updated_at") VALUES ($1, $2, $3) RETURNING "id"  [["padre_id", 5], ["created_at", "2018-11-20 17:31:21.737989"], ["updated_at", "2018-11-20 17:31:21.737989"]]

   (0.6ms)  COMMIT

=> true

irb(main):036:0> 

Or build from the belongs_to association on the other side:

irb(main):027:0> c = ChildTable.new

=> #<ChildTable id: nil, padre_id: nil, created_at: nil, updated_at: nil>

irb(main):028:0> c.build_main_table

=> #<MainTable custom_pk: nil, created_at: nil, updated_at: nil>

irb(main):029:0> c.save!

   (0.3ms)  BEGIN

  MainTable Create (0.8ms)  INSERT INTO "main_table" ("created_at", "updated_at") VALUES ($1, $2) RETURNING "custom_pk"  [["created_at", "2018-11-20 17:24:29.344332"], ["updated_at", "2018-11-20 17:24:29.344332"]]

  ChildTable Create (1.1ms)  INSERT INTO "child_table" ("padre_id", "created_at", "updated_at") VALUES ($1, $2, $3) RETURNING "id"  [["padre_id", 3], ["created_at", "2018-11-20 17:24:29.346764"], ["updated_at", "2018-11-20 17:24:29.346764"]]

   (0.7ms)  COMMIT

=> true

Not sure if it's the issue you're facing, but at the moment you're initializing new MainTables and ChildTables, however you're not saving them.

This means they won't be assigned an ID, which in turn means when you try and assign a Child Table to the Main Table, it doesn't have an ID for the main table (or itself) to create a join record with.

Try saving the records before shovelling in child records