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Kashif Soofi
Kashif Soofi

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REST API with Go, Chi, Postgres and sqlx

#rest #api #go #postgres

This is a continuation of an earlier post REST API with Go, Chi and InMemory Store. In this tutorial I will extend the service to store data in a Postgres database. I will use Docker to run Postgres and run database migrations.

Project Setup

I will start by copying the content of https://github.com/kashifsoofi/blog-code-samples/tree/main/movies-api-with-go-chi-and-memory-store, placing it in a new folder movies-api-with-go-chi-and-postgres and updating module name in go.mod to match the new folder and updating in source files where its used. This will usually be the root of your git repo and will not be as elaborate as this.

Setup Database Server

I will be using a docker-compose to run Postgres in a docker container. This would allow us the add more services that our rest api is depenedent on e.g. redis server for distributed caching.

Let's start by adding a new file named as docker-compose.dev-env.yml, feel free to name it as you like. Add following content to add a database instance for movies rest api.

version: '3.7'

services:
  movies.db:
    image: postgres:14-alpine
    environment:
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=Password123
      - POSTGRES_DB=moviesdb
    volumes:
      - moviesdbdata:/var/lib/postgresql/data/
    ports:
      - “5432:5432”
    restart: on-failure
    healthcheck:
      test: [ “CMD-SHELL”, “pg_isready -q -d moviesdb -U Password123“]
      timeout: 10s
      interval: 5s
      retries: 10

volumes:
  moviesdbdata:
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Open a terminal at the root of the solution where docker-compose file is location and execute following command to start database server.

docker-compose -f docker-compose.dev-env.yml up -d
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Database Migrations

Before we can start using Postgres we need to create a table to store our data. I will be using excellent migrate database migrations tool, it can also be imported as a libraray.

For migrations I have created a folder db and another folder named migrations under db. I executed following commands to create migrations.

migrate create -ext sql -dir db/migrations -seq extension_uuid_ossp_create
migrate create -ext sql -dir db/migrations -seq table_movies_create
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This would create 4 files, for each migration there would be an up and a down script, up would be executed when applying migration and down would be executed when rolling back a change.

  • 000001_extension_uuid_ossp_create.up.sql 
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
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  • 000001_extension_uuid_ossp_create.down.sql 
DROP EXTENSION IF EXISTS "uuid-ossp";
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  • 000002_table_movies_create.up.sql 
CREATE TABLE IF NOT EXISTS movies (
    id uuid PRIMARY KEY DEFAULT uuid_generate_v4(),
    title VARCHAR(100) NOT NULL,
    director VARCHAR(100) NOT NULL,
    release_date TIMESTAMP NOT NULL,
    ticket_price DECIMAL(12, 2) NOT NULL,
    created_at TIMESTAMP WITHOUT TIME ZONE DEFAULT (now() AT TIME ZONE 'utc') NOT NULL,
    updated_at TIMESTAMP WITHOUT TIME ZONE DEFAULT (now() AT TIME ZONE 'utc') NOT NULL
)
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  • 000002_table_movies_create.down.sql 
DROP TABLE IF EXISTS movies;
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I usually create a container that has all database migrations and tool to execute those migrations. Dockerfile to run database migrations is as follows

FROM migrate/migrate

# Copy all db files
COPY ./migrations /migrations

ENTRYPOINT [ "migrate", "-path", "/migrations", "-database"]
CMD ["postgresql://postgres:Password123@movies.db:5432/moviesdb?sslmode=disable up"]
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Add following in docker-compose.dev-env.yml file to add migrations container and run migrations on startup. Please remember if you add new migrations, you would need to delete container and movies.db.migrations image to add new migration files in the container.

  movies.db.migrations:
    depends_on:
      - movies.db
    image: movies.db.migrations
    build:
      context: ./db/
      dockerfile: Dockerfile
    command: "postgresql://postgres:Password123@movies.db:5432/moviesdb?sslmode=disable up"
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Open a terminal at the root of the project where docker-compose file is located and execute following command to start database server and apply migrations to create uuid-ossp extension and movies table.

docker-compose -f docker-compose.dev-env.yml up -d
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Postgres Movies Store

I will be using sqlx to execute queries and map columns to struct fields and vice versa, sqlx is a library which provides a set of extensions on go's standard database/sql library.

Add a new file named postgres_movies_store.go. Add a new struct PostgresMoviesStore containing databaseUrl and a pointer to sqlx.DB, also add helper methods to connect to database and close connection as well.

package store

import (
    "context"
    "movies-api/store"

    _ "github.com/jackc/pgx/stdlib"
    "github.com/jmoiron/sqlx"
)

const driverName = "pgx"

type PostgresMoviesStore struct {
    databaseUrl string
    dbx         *sqlx.DB
}

func NewPostgresMoviesStore(databaseUrl string) *PostgresMoviesStore {
    return &PostgresMoviesStore{
        databaseUrl: databaseUrl,
    }
}

func (s *PostgresMoviesStore) connect(ctx context.Context) error {
    dbx, err := sqlx.ConnectContext(ctx, driverName, s.databaseUrl)
    if err != nil {
        return err
    }

    s.dbx = dbx
    return nil
}

func (s *PostgresMoviesStore) close() error {
    return s.dbx.Close()
}
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Add db tags

Update Movie struct in movies_store.go file to add db tags, this allows sqlx to map struct members to column names.

type Movie struct {
    ID          uuid.UUID
    Title       string
    Director    string
    ReleaseDate time.Time `db:"release_date"`
    TicketPrice float64   `db:"ticket_price"`
    CreatedAt   time.Time `db:"created_at"`
    UpdatedAt   time.Time `db:"updated_at"`
}
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Context

We did not make use of the Context in the earlier sample movies-api-with-go-chi-and-memory-store, now that we are connecting to an external storage and package we are going to use to run queries support methods accepting Context we will update our store.Interface to accept Context and use that when running queries. store.Interface will be updated as follows

type Interface interface {
    GetAll(ctx context.Context) ([]Movie, error)
    GetByID(ctx context.Context, id uuid.UUID) (Movie, error)
    Create(ctx context.Context, createMovieParams CreateMovieParams) error
    Update(ctx context.Context, id uuid.UUID, updateMovieParams UpdateMovieParams) error
    Delete(ctx context.Context, id uuid.UUID) error
}
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We will also need to update MemoryMoviesStore methods to accept Context to satisfy store.Interface changes and update methods in movies_handler to pass request context using r.Context() when calling store methods.

Create

We connect to database using connect helper method, create a new instance of Movie and execute insert query with NamedExecContext. We are handling an error and return DuplicateKeyError if SqlState of exception is 23505. If insert is successful then we return nil.
Create function looks like

func (s *PostgresMoviesStore) Create(ctx context.Context, createMovieParams CreateMovieParams) error {
    err := s.connect(ctx)
    if err != nil {
        return err
    }
    defer s.close()

    movie := Movie{
        ID:          createMovieParams.ID,
        Title:       createMovieParams.Title,
        Director:    createMovieParams.Director,
        ReleaseDate: createMovieParams.ReleaseDate,
        TicketPrice: createMovieParams.TicketPrice,
        CreatedAt:   time.Now().UTC(),
        UpdatedAt:   time.Now().UTC(),
    }

    if _, err := s.dbx.NamedExecContext(
        ctx,
        `INSERT INTO movies
            (id, title, director, release_date, ticket_price, created_at, updated_at)
        VALUES
            (:id, :title, :director, :release_date, :ticket_price, :created_at, :updated_at)`,
        movie); err != nil {
        if strings.Contains(err.Error(), "SQLSTATE 23505") {
            return &DuplicateKeyError{ID: createMovieParams.ID}
        }
        return err
    }

    return nil
}
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GetAll

We connect to database using connect helper method, then use SelectContext method of sqlx to execute query, sqlx would map the columns to fields. If query is successful then we return the slice of loaded movies.

func (s *PostgresMoviesStore) GetAll(ctx context.Context) ([]Movie, error) {
    err := s.connect(ctx)
    if err != nil {
        return nil, err
    }
    defer s.close()

    var movies []Movie
    if err := s.dbx.SelectContext(
        ctx,
        &movies,
        `SELECT
            id, title, director, release_date, ticket_price, created_at, updated_at
        FROM movies`); err != nil {
        return nil, err
    }

    return movies, nil
}
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GetByID

We connect to database using connect helper method, then use GetContext method to execute select query, sqlx would map the columns to fields. If the driver returns sql.ErrNoRows then we return store.RecordNotFoundError. If successful loaded movie record is returned.

func (s *PostgresMoviesStore) GetByID(ctx context.Context, id uuid.UUID) (Movie, error) {
    err := s.connect(ctx)
    if err != nil {
        return Movie{}, err
    }
    defer s.close()

    var movie Movie
    if err := s.dbx.GetContext(
        ctx,
        &movie,
        `SELECT
            id, title, director, release_date, ticket_price, created_at, updated_at
        FROM movies
        WHERE id = $1`,
        id); err != nil {
        if err != sql.ErrNoRows {
            return Movie{}, err
        }

        return Movie{}, &RecordNotFoundError{}
    }

    return movie, nil
}
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Update

We connect to database using connect helper method, then use NamedExecContext method to execute query to update an existing record.

func (s *PostgresMoviesStore) Update(ctx context.Context, id uuid.UUID, updateMovieParams UpdateMovieParams) error {
    err := s.connect(ctx)
    if err != nil {
        return err
    }
    defer s.close()

    movie := Movie{
        ID:          id,
        Title:       updateMovieParams.Title,
        Director:    updateMovieParams.Director,
        ReleaseDate: updateMovieParams.ReleaseDate,
        TicketPrice: updateMovieParams.TicketPrice,
        UpdatedAt:   time.Now().UTC(),
    }

    if _, err := s.dbx.NamedExecContext(
        ctx,
        `UPDATE movies
        SET title = :title, director = :director, release_date = :release_date, ticket_price = :ticket_price, updated_at = :updated_at
        WHERE id = :id`,
        movie); err != nil {
        return err
    }

    return nil
}
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Delete

We connect to database using connect helper method, then execute query to delete an existing record using ExecContext.

func (s *PostgresMoviesStore) Delete(ctx context.Context, id uuid.UUID) error {
    err := s.connect(ctx)
    if err != nil {
        return err
    }
    defer s.close()

    if _, err := s.dbx.ExecContext(
        ctx,
        `DELETE FROM movies
        WHERE id = $1`, id); err != nil {
        return err
    }

    return nil
}
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Database Configuration

Add a new struct named Database in config.go and add that to Configuration struct as well.

type Configuration struct {
    HTTPServer
    Database
}
...
type Database struct {
    DatabaseURL        string `envconfig:"DATABASE_URL" required:"true"`
    LogLevel           string `envconfig:"DATABASE_LOG_LEVEL" default:"warn"`
    MaxOpenConnections int    `envconfig:"DATABASE_MAX_OPEN_CONNECTIONS" default:"10"`
}
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Dependency Injection

Update main.go as follows to create a new instance of PostgresMoviesStore, I have opted to create instance of PostgresMoviesStore instead of MemoryMoviesStore, solution can be enhanced to create either one of the dependency based on a configuration.

// store := store.NewMemoryMoviesStore()
store := store.NewPostgresMoviesStore(cfg.DatabaseURL)
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Test

I am not adding any unit or integration tests for this tutorial, perhaps a following tutorial. But all the endpoints can be tested either using Postman for by following test plan from previous article.

You can start rest api with postgres by executing following

DATABASE_URL=postgresql://postgres:Password123@localhost:5432/moviesdb?sslmode=disable go run main.go
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Source

Source code for the demo application is hosted on GitHub in blog-code-samples repository.

References

In no particular order

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