Retrospectively change ecto column data type

Questions / Help
,
1

I created this schema with the :amount field being of type ‘float’. I now want it to be a decimal - so I have changed it and migrated the changes:

defmodule SpBank.Account.User do
  use Ecto.Schema
  import Ecto.Changeset
  alias SpBank.Account.Transaction
  schema "users" do
    # field :id 
    field :amount, :decimal
    field :name, :string
    has_many :transactions, Transaction 
    timestamps()
  end

  @doc false
  def changeset(user, attrs) do
    user
    |> cast(attrs, [:name, :amount])
    |> validate_required([:name, :amount])
  end
end

However I am getting an error that amount is still a float when I try to insert 90 into the amount field:
# Postgrex expected a float, got #Decimal<90>. Please make sure the value you are passing matches the definition in your table or in your query or convert the value accordingly.

Why is this and how do I properly change the data taype of the column in the schema?

2

Unless your data is important, You can run…

mix ecto.reset

This will drop the database, recreate and migrate again under a Phoenix project.

Otherwise, the recommended way is to use a migration to alter a table.

Don’t forget to change the migration file and the schema :slight_smile:

1 Like
3

Ok I’ll try that thanks. FOr future reference, how would you migrate an alteration to this table so that the data type of the column changes as I already tried this but ecto.migrate returned an error for ‘no alter function found’?

4

SO I just reset the database and re-migrated it - still having the same error : Postgrex expected a float, got #Decimal<90>. Please make sure the value you are passing matches the definition in your table or in your query or convert the value accordingly.

5

Please show your migration file…

6 
defmodule SpBank.Account.User do
  use Ecto.Schema
  import Ecto.Changeset
  alias SpBank.Account.Transaction
  schema "users" do
    # field :id 
    field :amount, :decimal
    field :name, :string
    has_many :transactions, Transaction 
    timestamps()
  end

  @doc false
  def changeset(user, attrs) do
    user
    |> cast(attrs, [:name, :amount])
    |> validate_required([:name, :amount])
  end
end

alter table("users") do
  modify :amount, :decimal
end

let me know if you meant a different file, this is all new to me!

7 
defmodule SpBank.Repo.Migrations.CreateUsers do
  use Ecto.Migration

  def change do
    create table(:users) do
      add :name, :string
      add :amount, :decimal

      timestamps()
    end

  end
end
8

The migration file is located in priv/repo/migrations and should be called create_users…

The db type should be :decimal, and the Elixir type should Decimal.

9

Sorry I put this comment just after my earlier one. It is showing the amount as ‘:decimal’, not float soo I am not sure why it seems to think it is a type float.

defmodule SpBank.Repo.Migrations.CreateUsers do
  use Ecto.Migration

  def change do
    create table(:users) do
      add :name, :string
      add :amount, :decimal

      timestamps()
    end

  end
end
10

Did You reset tables after update?

11

Ah for some reason when I tried ecto.reset this time, it actually worked - no idea why but thank you, much appreciated! :slight_smile: