Repo, Changesets y consultas
Use `Ecto.Repo` para interactuar con bases de datos, `Changesets` para validar datos y cree consultas con `Ecto.Query`.
Repo, Changesets y consultas es una lección gratuita de Elixir & Phoenix: Scalable Backend Development en CoddyKit. Esta es la lección 2 de 4. Puedes leer la lección completa abajo gratuitamente — luego la practicas en el navegador con un editor de código integrado y un tutor de IA 24/7. Forma parte de la ruta de aprendizaje de Elixir & Phoenix: Scalable Backend Development, y tu progreso se sincroniza en la web y la app de CoddyKit. El curso de Elixir & Phoenix: Scalable Backend Development incluye 4 lecciones en total.
Partes de esta lección aún no han sido traducidas y se muestran en inglés.
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()"Retrieving Records with Repo
You can fetch records from the database using Ecto.Repo.get/3 to retrieve a single record by its primary key, or Ecto.Repo.all/2 to get multiple records.
get(Schema, id): Fetches one record by ID. Returns the struct ornil.all(Query): Fetches all records matching a given query.
defmodule MyApp.Product do
use Ecto.Schema
schema "products" do
field :name, :string
field :price, :decimal
field :stock, :integer, default: 0
timestamps()
end
end
defmodule MyApp.SimulatedRepo do
alias MyApp.Product
def get(id, _query \\ nil) do
IO.puts "Simulating fetching product with ID: #{id}"
case id do
1 -> %Product{id: 1, name: "Laptop", price: Decimal.new("1200.00"), stock: 5,
inserted_at: NaiveDateTime.utc_now(), updated_at: NaiveDateTime.utc_now()}
_ -> nil
end
end
def all(_query \\ nil) do
IO.puts "Simulating fetching all products..."
[
%Product{id: 1, name: "Laptop", price: Decimal.new("1200.00"), stock: 5,
inserted_at: NaiveDateTime.utc_now(), updated_at: NaiveDateTime.utc_now()},
%Product{id: 2, name: "Mouse", price: Decimal.new("25.50"), stock: 20,
inserted_at: NaiveDateTime.utc_now(), updated_at: NaiveDateTime.utc_now()}
]
end
end
defmodule FetchExample do
alias MyApp.SimulatedRepo
def run() do
# Fetch a single product by ID
IO.puts "\n--- Fetching by ID ---"
product = SimulatedRepo.get(1)
IO.inspect product
# Fetch all products
IO.puts "\n--- Fetching all ---"
products = SimulatedRepo.all()
IO.inspect products
end
end
# To run this, execute: elixir -e "FetchExample.run()"Data Safety with Changesets
Ecto.Changeset is a powerful mechanism for validating, casting, and manipulating data before it interacts with your database. It ensures data integrity and security.
Instead of directly passing raw user input to the database, you first pass it through a changeset. The changeset tracks all proposed changes and any associated errors.
- Casting: Converts input data into the correct Elixir types.
- Validation: Checks if the data meets predefined rules (e.g., required fields, data formats).
- Authorization: Can even be used for field-level permission checks.
Casting and Basic Validation
The first step with a changeset is usually Ecto.Changeset.cast/4. This function takes a struct (or an empty struct), parameters (like user input), and a list of allowed fields. It converts the input into the correct types.
After casting, you can apply validations like validate_required/3 to ensure essential fields are present.
defmodule MyApp.User do
use Ecto.Schema
import Ecto.Changeset
schema "users" do
field :name, :string
field :email, :string
field :age, :integer
end
def changeset(user, attrs) do
user
|> cast(attrs, [:name, :email, :age])
|> validate_required([:name, :email])
end
end
defmodule ChangesetCastValidateExample do
alias MyApp.User
def run() do
IO.puts "--- Valid Input ---"
valid_params = %{"name" => "Alice", "email" => "alice@example.com", "age" => "30"}
valid_changeset = User.changeset(%User{}, valid_params)
IO.puts "Is valid? #{Ecto.Changeset.valid?(valid_changeset)}"
IO.inspect Ecto.Changeset.changes(valid_changeset)
IO.puts "\n--- Invalid Input (missing email) ---"
invalid_params = %{"name" => "Bob", "age" => "25"}
invalid_changeset = User.changeset(%User{}, invalid_params)
IO.puts "Is valid? #{Ecto.Changeset.valid?(invalid_changeset)}"
IO.inspect Ecto.Changeset.errors(invalid_changeset)
end
end
# To run this, execute: elixir -e "ChangesetCastValidateExample.run()"Deeper Changeset Validations
Beyond basic requirements, Ecto offers many validation helpers to enforce specific rules:
validate_length/3: Checks string length.validate_number/3: Validates numeric ranges.validate_format/3: Uses regular expressions for complex patterns (e.g., email format).
These help you build robust data models.
defmodule MyApp.User do
use Ecto.Schema
import Ecto.Changeset
schema "users" do
field :name, :string
field :email, :string
field :age, :integer
end
def changeset(user, attrs) do
user
|> cast(attrs, [:name, :email, :age])
|> validate_required([:name, :email])
|> validate_length(:name, min: 3, max: 50)
|> validate_number(:age, greater_than_or_equal_to: 18)
|> validate_format(:email, ~r/@/, message: "must contain an @ symbol")
end
end
defmodule ChangesetDeepValidateExample do
alias MyApp.User
def run() do
IO.puts "--- Valid User ---"
user_attrs_1 = %{"name" => "Charlie", "email" => "charlie@example.com", "age" => "22"}
changeset_1 = User.changeset(%User{}, user_attrs_1)
IO.puts "Valid? #{Ecto.Changeset.valid?(changeset_1)}"
IO.inspect Ecto.Changeset.errors(changeset_1)
IO.puts "\n--- Invalid User (short name, young age, bad email) ---"
user_attrs_2 = %{"name" => "Al", "email" => "al.example.com", "age" => "17"}
changeset_2 = User.changeset(%User{}, user_attrs_2)
IO.puts "Valid? #{Ecto.Changeset.valid?(changeset_2)}"
IO.inspect Ecto.Changeset.errors(changeset_2)
end
end
# To run this, execute: elixir -e "ChangesetDeepValidateExample.run()"Applying Changeset Actions
Once a changeset is validated, you can use it to perform database actions like inserting or updating records. The Ecto.Changeset.valid?/1 function tells you if the changeset is ready.
If invalid, Ecto.Changeset.errors/1 will provide a detailed list of what went wrong, which is crucial for providing user feedback.
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)
end
end
defmodule ChangesetApplyExample do
alias MyApp.Product
def run() do
IO.puts "--- Valid Product Changeset ---"
valid_attrs = %{"name" => "Widget", "price" => "9.99", "stock" => "50"}
valid_changeset = Product.changeset(%Product{}, valid_attrs)
if Ecto.Changeset.valid?(valid_changeset) do
IO.puts "Changeset is valid. Proposed changes:"
IO.inspect Ecto.Changeset.changes(valid_changeset)
# In a real app, you'd call Repo.insert(valid_changeset) here
else
IO.puts "Changeset is invalid. Errors:"
IO.inspect Ecto.Changeset.errors(valid_changeset)
end
IO.puts "\n--- Invalid Product Changeset (missing price) ---"
invalid_attrs = %{"name" => "Gadget", "stock" => "20"}
invalid_changeset = Product.changeset(%Product{}, invalid_attrs)
if Ecto.Changeset.valid?(invalid_changeset) do
IO.puts "Changeset is valid. Proposed changes:"
IO.inspect Ecto.Changeset.changes(invalid_changeset)
else
IO.puts "Changeset is invalid. Errors:"
IO.inspect Ecto.Changeset.errors(invalid_changeset)
end
end
end
# To run this, execute: elixir -e "ChangesetApplyExample.run()"Building Queries with Ecto.Query
While Repo.get/3 and Repo.all/2 are useful for simple fetches, Ecto.Query provides a powerful, composable language for building complex database queries.
You start a query with the from macro, specifying the schema you want to query and giving it an alias.
Ecto queries are Elixir expressions that are translated into SQL by Ecto.
defmodule MyApp.Product do
use Ecto.Schema
schema "products" do
field :name, :string
field :price, :decimal
field :stock, :integer, default: 0
end
end
defmodule EctoQueryFromExample do
import Ecto.Query
alias MyApp.Product
def run() do
# A simple query to select all products
query = from p in Product
IO.puts "Basic query structure:"
IO.inspect query
IO.puts "\n(Note: This only shows the query structure, not execution against a DB.)"
end
end
# To run this, execute: elixir -e "EctoQueryFromExample.run()"Querying: Filtering & Selecting
You can refine your queries using clauses like where to filter records based on conditions, and select to specify which fields you want to retrieve.
where: p.stock > 0: Filters records where stock is greater than 0.select: p.name: Retrieves only the 'name' field.
defmodule MyApp.Product do
use Ecto.Schema
schema "products" do
field :name, :string
field :price, :decimal
field :stock, :integer, default: 0
end
end
defmodule EctoQueryWhereSelectExample do
import Ecto.Query
alias MyApp.Product
def run() do
# Query for products with stock > 0, selecting only their names
query = from p in Product,
where: p.stock > 0,
select: p.name
IO.puts "Query structure with where and select:"
IO.inspect query
IO.puts "\n(Note: This only shows the query structure, not execution against a DB.)"
end
end
# To run this, execute: elixir -e "EctoQueryWhereSelectExample.run()"Querying: Ordering & Limiting
To control the presentation of your results, you can use order_by to sort records and limit to restrict the number of records returned.
order_by: [desc: p.price]: Sorts by price in descending order.limit: 5: Returns only the first 5 matching records.
These are crucial for pagination and displaying sorted lists.
defmodule MyApp.Product do
use Ecto.Schema
schema "products" do
field :name, :string
field :price, :decimal
field :stock, :integer, default: 0
end
end
defmodule EctoQueryOrderLimitExample do
import Ecto.Query
alias MyApp.Product
def run() do
# Query for products, ordered by price descending, limited to 3
query = from p in Product,
order_by: [desc: p.price],
limit: 3
IO.puts "Query structure with order_by and limit:"
IO.inspect query
IO.puts "\n(Note: This only shows the query structure, not execution against a DB.)"
end
end
# To run this, execute: elixir -e "EctoQueryOrderLimitExample.run()"Quick Check: Ecto Core
Which of the following statements about Ecto.Changeset is TRUE?
Recap: Repo, Changesets & Queries
Great job! In this lesson, you've learned the core components for data persistence in Elixir with Ecto:
- Ecto.Repo: The gateway for all database interactions.
- Ecto.Changeset: Essential for casting, validating, and tracking changes to your data, ensuring integrity.
- Ecto.Query: A powerful and flexible way to construct complex database queries using Elixir syntax.
Mastering these three pillars is fundamental to building robust and reliable data-driven applications in Elixir!
Preguntas frecuentes
¿La lección «Repo, Changesets y consultas» es gratis?
Sí — el texto completo de «Repo, Changesets y consultas» es gratis para leer aquí en la web. Para practicarla de forma interactiva (editor de código integrado y tutor de IA 24/7) y desbloquear el resto del curso de Elixir & Phoenix: Scalable Backend Development, actualiza a CoddyKit PRO. El curso de Elixir & Phoenix: Scalable Backend Development incluye 4 lecciones en total.
¿Qué aprenderé en «Repo, Changesets y consultas»?
Use `Ecto.Repo` para interactuar con bases de datos, `Changesets` para validar datos y cree consultas con `Ecto.Query`. Practicas Elixir & Phoenix: Scalable Backend Development con código real que ejecutas directamente en el navegador, y un tutor de IA 24/7 responde tus preguntas mientras trabajas en la lección.
¿Necesito experiencia previa para empezar Elixir & Phoenix: Scalable Backend Development?
No se requiere experiencia previa. Elixir & Phoenix: Scalable Backend Development en CoddyKit está estructurado para principiantes hasta estudiantes avanzados, así que puedes empezar aquí o desde el inicio y avanzar a tu ritmo. Esta es la lección 2 de 4.
¿Cuánto tiempo toma la lección «Repo, Changesets y consultas»?
La mayoría de las lecciones de CoddyKit toman alrededor de 5–10 minutos. Cada una es compacta e interactiva, así que avanzas constantemente y retomas exactamente por donde dejaste en la web y la app.
¿Puedo escribir y ejecutar código en esta lección de Elixir & Phoenix: Scalable Backend Development?
Sí. Cada lección de Elixir & Phoenix: Scalable Backend Development incluye un editor de código integrado, así que escribes y ejecutas código real directamente en tu navegador y obtienes retroalimentación instantánea de IA — sin configuración local necesaria.
Todas las lecciones de este curso
- Esquemas de Ecto y migraciones de bases de datos
- Repo, Changesets y consultas
- Asociaciones y esquemas embebidos
- Transacciones y Ecto.Multi