How to Add a Field to a Generated Table Retroactively

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First, generated data is created. This is an example:

mix phx.gen.html TestBeds TestBed  testbeds name:string url:string

Generate a migration file

To add a field, you must first generate a migration file. The migration file is an empty file that is generated using a command. After it is generated you write code and invoke it.

The command is:

mix ecto.gen.migration name_of_migration

For this example, I will add a new field named owner

mix ecto.gen.migration create_owner_field

The migration file after it is created appears in app/priv/migrations

In the terminal run:

mix ecto.migrate

The field is created but the HTML, controllers and tests are not. You need to manually replicate that code. Use prerecreated Generated field code as a reference.