# ChangesetHelpers

This library provides a set of helper functions to work with Ecto Changesets.

### `validate_comparison(changeset, field1, operator, field2_or_value, opts)`

Validates the result of the comparison of
  * two fields (where at least one is a change) or
  * a change and a value, where the value is an integer, a `Date`, a `Time`,
    a `DateTime` or a `NaiveDateTime`.

```elixir
validate_comparison(changeset, :start_time, :lt, :end_time)

assert [start_time: {"must be less than 10:00:00", [validation: :comparison]}] = changeset.errors
assert [start_time: :comparison, end_time: :comparison] = changeset.validations
```

```elixir
validate_comparison(appointment_changeset, :end_time, :lt, ~T[21:00:00])

assert [end_time: {"must be less than 21:00:00", [validation: :comparison]}] = changeset.errors
assert [end_time: :comparison] = changeset.validations
```

### `validate_list(changeset, field, validation_fun, validation_fun_args)`

Validates a list of values using the given validator.

```elixir
changeset =
  %Appointment{}
  |> Appointment.changeset(%{days_of_week: [1, 3, 8]})
  |> validate_list(:days_of_week, &Ecto.Changeset.validate_inclusion/3, [1..7])

assert [days_of_week: {"is invalid", [validation: :list, index: 2, validator: :validate_inclusion]}] = changeset.errors
assert [days_of_week: {:list, [validator: :validate_inclusion]}] = changeset.validations
```

As the validator function is from the `Ecto.Changeset` module, you may just write `:validate_inclusion`.

### `put_assoc(changeset, keys, value)`

Puts the given nested association in the changeset through a given list of field names.

```elixir
ChangesetHelpers.put_assoc(account_changeset, [:user, :config, :address], address_changeset)
```

Instead of giving a Changeset or a schema as the third argument, a function may also be given in order to modify the
nested changeset in one go.

```elixir
ChangesetHelpers.put_assoc(account_changeset, [:user, :articles],
  &(Enum.concat(&1, [%Article{} |> Ecto.Changeset.change()])))
```

In the code above, we change a new empty Article, and add the changeset into the articles association (typically done when we want to add a new
row of form inputs to add an entity into a form handling a nested collection of entities).

### `put_assoc(changeset, keys, index, value)`

Puts the given nested association in the changeset through a given list of field names, at the given index.

### `change_assoc(struct_or_changeset, keys, changes \\ %{})`

Returns the nested association in a changeset. This function will first look into the changes and then fails back on
data wrapped in a changeset.

Changes may be added to the given changeset through the third argument.

A tuple is returned containing the modified root changeset and the changeset of the association.

```elixir
{account_changeset, address_changeset} =
  change_assoc(account_changeset, [:user, :user_config, :address], %{street: "Foo street"})
```

### `change_assoc(struct_or_changeset, keys, index, changes \\ %{})`

Returns the nested association in a changeset at the given index.

### `fetch_field(changeset, keys)`

Fetches the given nested field from changes or from the data.

```elixir
{:changes, street} =
  ChangesetHelpers.fetch_field(account_changeset, [:user, :config, :address, :street])
```

### `fetch_field!(changeset, keys)`

Same as `fetch_field/2` but returns the value or raises if the given nested key was not found.

```elixir
street = ChangesetHelpers.fetch_field!(account_changeset, [:user, :config, :address, :street])
```

### `fetch_change(changeset, keys)`

Fetches the given nested field from changes or from the data.

```elixir
{:ok, street} =
  ChangesetHelpers.fetch_change(account_changeset, [:user, :config, :address, :street])
```

### `fetch_change!(changeset, keys)`

Same as `fetch_change/2` but returns the value or raises if the given nested key was not found.

```elixir
street = ChangesetHelpers.fetch_change!(account_changeset, [:user, :config, :address, :street])
```

### `diff_field(changeset1, changeset2, keys)`

This function allows checking if a given field is different in two changesets.

```elixir
{street_changed, street1, street2} =
  diff_field(account_changeset, new_account_changeset, [:user, :user_config, :address, :street])
```

### `add_error(changeset, keys, message, extra \\ [])`

Adds an error to the nested changeset.

```elixir
ChangesetHelpers.add_error(account_changeset, [:user, :articles, :error_key], "Some error")
```

### `field_fails_validation?(changeset, field, validations)`

Checks whether a field as the given validation error key.

```elixir
field_fails_validation?(changeset, :email, :unsafe_unique)
```

### `field_violates_constraint?(changeset, field, constraints)`

Checks whether a field as the given constraint error key.

```elixir
field_violates_constraint?(changeset, :email, :unique)
```

### `validate_changes(changeset, fields, meta, validator)`

Works like `Ecto.Changeset.validate_change/3` but may receive multiple fields.

## Installation

Add `changeset_helpers` for Elixir as a dependency in your `mix.exs` file:

```elixir
def deps do
  [
    {:changeset_helpers, "~> 0.17.0"}
  ]
end
```

## HexDocs

HexDocs documentation can be found at [https://hexdocs.pm/changeset_helpers](https://hexdocs.pm/changeset_helpers).