Elixir & Phoenix: Scalable Backend Development · Lesson

Repo, Changesets, and Queries

Use `Ecto.Repo` for database interactions, `Changesets` for data validation, and build queries with `Ecto.Query`.

Ecto.Repo: Database Gateway

In Elixir, Ecto.Repo is your primary interface for interacting with your database. Think of it as the central hub that handles all your database operations.

It provides functions for inserting, updating, deleting, and querying records, abstracting away the specifics of the underlying database technology.

Connects your Elixir application to the database.
Manages database transactions.
Executes Ecto queries.

Saving Data with Repo.insert

To add new data to your database, you'll use Ecto.Repo.insert/2. This function takes a changeset (which we'll cover next) and attempts to save it as a new record.

If successful, it returns {:ok, record}; otherwise, it returns {:error, changeset} with validation errors.

defmodule MyApp.Product do
  use Ecto.Schema
  import Ecto.Changeset

  schema "products" do
    field :name, :string
    field :price, :decimal
    field :stock, :integer, default: 0
    timestamps()
  end

  def changeset(product, attrs) do
    product
    |> cast(attrs, [:name, :price, :stock])
    |> validate_required([:name, :price])
    |> validate_number(:price, greater_than: 0)
    |> validate_number(:stock, greater_than_or_equal_to: 0)
  end
end

defmodule MyApp.SimulatedRepo do
  alias MyApp.Product

  def insert(changeset) do
    if Ecto.Changeset.valid?(changeset) do
      data = Ecto.Changeset.apply_action(changeset, :insert)
      # Simulate successful insert with a mock ID and timestamps
      {:ok, %Product{data | id: 1, inserted_at: NaiveDateTime.utc_now(), updated_at: NaiveDateTime.utc_now()}}
    else
      {:error, changeset}
    end
  end
end

defmodule InsertExample do
  alias MyApp.{Product, SimulatedRepo}

  def run() do
    # Prepare product attributes
    attrs = %{name: "Elixir Book", price: Decimal.new("39.99"), stock: 100}

    # Create a changeset
    changeset = Product.changeset(%Product{}, attrs)

    # Simulate inserting the product
    case SimulatedRepo.insert(changeset) do
      {:ok, product} ->
        IO.puts "Successfully inserted product:"
        IO.inspect product
      {:error, changeset} ->
        IO.puts "Failed to insert product:"
        IO.inspect Ecto.Changeset.errors(changeset)
    end
  end
end

# To run this, execute: elixir -e "InsertExample.run()"

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