REST API with Go, Chi, SQL Server and sqlx
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 Microsoft SQL Server database. I will be using Microsoft SQL Server - Ubuntu based images for this sample. I will use Docker to run SQL Server and use the same to run database migrations.
Setup Database Server
I will be using a docker-compose to run SQL Server 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.
We will be using a custom image for our instance of SQL Server. Reason for this is that SQL Server container does not have built in funcationality to create a custom application database that MySQL and Postgres provide using environment variables. We have a setup-db.sql that we will copy in our custom image and execute as part of the health check in docker-compose configuration.
Let’s start by adding Dockerfile.db under db folder.
FROM mcr.microsoft.com/mssql/server:2022-latest
WORKDIR /scripts
COPY setup-db.sql /scripts/setup-db.sql
ENTRYPOINT [ "/opt/mssql/bin/sqlservr" ]
Here is the setup-db.sql file, also located in db folder, I am only creating a database but this is a good place to add an application user, role and set permissions.
IF NOT EXISTS(SELECT * FROM sys.databases WHERE name = 'Movies')
BEGIN
CREATE DATABASE Movies
SELECT 'READY'
END
Let’s add 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: movies.db
build:
context: ./db/
dockerfile: Dockerfile.db
environment:
- ACCEPT_EULA=Y
- MSSQL_SA_PASSWORD=Password123
- MSSQL_PID=Express
volumes:
- moviesdbdata:/var/opt/mssql
ports:
- "1433:1433"
healthcheck:
test: '/opt/mssql-tools/bin/sqlcmd -U sa -P Password123 -i /scripts/setup-db.sql | grep -q "READY"'
timeout: 20s
interval: 10s
retries: 10
volumes:
moviesdbdata:
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
Database Migrations
Before we can start using SQL Server 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 migrations under db folder. I executed following commands to create migrations.
migrate create -ext sql -dir db/migrations -seq table_movies_create
This would create 2 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_table_movies_create.up.sqlIF NOT EXISTS (SELECT * FROM sysobjects WHERE name='Movies' and xtype='U') BEGIN CREATE TABLE Movies ( Id UNIQUEIDENTIFIER NOT NULL PRIMARY KEY, Title VARCHAR(100) NOT NULL, Director VARCHAR(100) NOT NULL, ReleaseDate DateTimeOffset NOT NULL, TicketPrice DECIMAL(12, 4) NOT NULL, CreatedAt DateTimeOffset NOT NULL, UpdatedAt DateTimeOffset NOT NULL ) END000001_table_movies_create.down.sqlIF NOT EXISTS (SELECT * FROM sysobjects WHERE name='Movies' and xtype='U') BEGIN DROP TABLE Movies END
I usually create a container that has all database migrations and tool to execute those migrations. Dockerfile.migrations to run database migrations is as follows
FROM migrate/migrate
# Copy all db files
COPY ./migrations /migrations
ENTRYPOINT [ "migrate", "-path", "/migrations", "-database"]
CMD ["sqlserver://sa:Password123@movies.db:1433/Movies up"]
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 image.
movies.db.migrations:
depends_on:
movies.db:
condition: service_healthy
image: movies.db.migrations
build:
context: ./db/
dockerfile: Dockerfile.migrations
command: "sqlserver://sa:Password123@movies.db:1433/Movies up"
Open a terminal at the root of the project where docker-compose file is location and execute following command to start database server and apply migrations to create Movies schema and Movies table.
docker-compose -f docker-compose.dev-env.yml up -d
SQL Server 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 sqlserver_movies_store.go under store folder. Add a new struct SqlServerMoviesStore containing databaseUrl and a pointer to sqlx.DB, also add helper methods to connect to database and close connection as well. Also note that I have added a noOpMapper method and set as MapperFunc of sqlx.DB, reason for this is to use the same casing as the struct field name. Default behaviour for sqlx is to map field names to lower case column names.
package sqlserver
import (
"context"
"github.com/jmoiron/sqlx"
_ "github.com/microsoft/go-mssqldb"
)
const driverName = "sqlserver"
type SqlServerMoviesStore struct {
databaseUrl string
dbx *sqlx.DB
}
func NewSqlServerMoviesStore(databaseUrl string) *SqlServerMoviesStore {
return &SqlServerMoviesStore{
databaseUrl: databaseUrl,
}
}
func noOpMapper(s string) string { return s }
func (s *SqlServerMoviesStore) connect(ctx context.Context) error {
dbx, err := sqlx.ConnectContext(ctx, driverName, s.databaseUrl)
if err != nil {
return err
}
dbx.MapperFunc(noOpMapper)
s.dbx = dbx
return nil
}
func (s *SqlServerMoviesStore) close() error {
return s.dbx.Close()
}
Add db tag
Update Movie struct in movies_store.go file to add db tag for ID field, this allows sqlx to map ID field to correct column. Alternative to this is to use the AS in select queries or update the column name in database table as ID. All other fields will be mapped correctly by using noOpMapper from the above section.
type Movie struct {
ID uuid.UUID `db:"Id"`
...
}
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
}
We will also need to update MemoryMoviesStore methods to accept Context to satisfy store.Interface 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 DuplicateIdError if returned error contains text Cannot insert duplicate key. If insert is successful then we return nil.
Create function looks like
func (s *SqlServerMoviesStore) 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, ReleaseDate, TicketPrice, CreatedAt, UpdatedAt)
VALUES
(:Id, :Title, :Director, :ReleaseDate, :TicketPrice, :CreatedAt, :UpdatedAt)`,
movie); err != nil {
if strings.Contains(err.Error(), "Cannot insert duplicate key") {
return &DuplicateKeyError{ID: createMovieParams.ID}
}
return err
}
return nil
}
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 *SqlServerMoviesStore) 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, ReleaseDate, TicketPrice, CreatedAt, UpdatedAt
FROM Movies`); err != nil {
return nil, err
}
return movies, nil
}
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.
Please note sql.Named query paramter, this is needed by the sql server driver to pass named parameters.
func (s *SqlServerMoviesStore) 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, ReleaseDate, TicketPrice, CreatedAt, UpdatedAt
FROM Movies
WHERE Id = @id`,
sql.Named("id", id)); err != nil {
if err != sql.ErrNoRows {
return Movie{}, err
}
return Movie{}, &RecordNotFoundError{}
}
return movie, nil
}
Update
We connect to database using connect helper method, then use NamedExecContext method to execute query to update an existing record.
func (s *SqlServerMoviesStore) 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, ReleaseDate = :ReleaseDate, TicketPrice = :TicketPrice, UpdatedAt = :UpdatedAt
WHERE Id = :Id`,
movie); err != nil {
return err
}
return nil
}
Delete
We connect to database using connect helper method, then execute query to delete an existing record using ExecContext.
func (s *SqlServerMoviesStore) 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 = @id`, sql.Named("id", id)); err != nil {
return err
}
return nil
}
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"`
}
Dependency Injection
Update main.go as follows to create a new instance of SqlServerMoviesStore, I have opted to create instance of SqlServerMoviesStore instead of MemoryMoviesStore, solution can be enhanced to create either one of the dependency based on a configuration.
// store := store.NewMemoryMoviesStore()
store := store.NewSqlServerMoviesStore(cfg.DatabaseURL)
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 SQL Server running in docker by executing following
DATABASE_URL=sqlserver://sa:Password123@localhost:1433/Movies go run main.go
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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