remvn

Posted on Sep 27

Write raw SQL easier with pgx and sqlc in Go

#go #database

What is pgx and sqlc?

pgx: a robust toolkit and PostgreSQL driver for Golang. This module also provides some useful tool for handling complex queries easier and less error-prone.
sqlc: a code generator tool that turns your SQL queries in .sql files into Go code with type-safe for both query params and query result. Check out an example here: sqlc playground. sqlc also supports pgx out of the box, which makes this a great combination for your database's need.

Why the combination of pgx and sqlc?

Although you may want to use some alternative solution like GORM (A Database ORM in Go), It seems like an easy choice to implement and use, plus you don't have to write SQL. Sounds too good to be true... but here's the catch:

Based on my experience, almost all ORM I have ever used only perform well in easy scenarios (eg CRUD operation). The more complex your query gets, the harder to implement properly in these ORM, sometime it's even harder than writing raw query manually (try adding an upsert or CTE), to the point you have to pull out the big gun... yes, you grab the database driver under the wrapper and start writing raw sql, map the types manually and questioning yourself why you chose to use an ORM in the first place.

Another foot gun of ORM is that you generally can't control the SQL query they produce, they may do dumb things and write terrible queries. Here's a funny story about Prisma ORM in javascript world: video

A balance spot between error-prone, untyped raw query and ORM is query builder. They provide some sort of type safety and the flexibility to build and optimize complex query.

Usage of sqlc

sqlc is not exactly a query builder but a code generator that reads your
queries and schema in .sql files and turns it into type-safe code for both query params and query result, for example:

It turns this query: (note that the comment is mandatory)

-- name: CreateAuthor :one
INSERT INTO author (name, bio)
VALUES (lower(@name), @bio)
RETURNING *;

Into this type-safe Go code, ready to use:

const createAuthor = `-- name: CreateAuthor :one
INSERT INTO author (name, bio)
VALUES (lower($1), $2)
RETURNING id, name, bio
`

type CreateAuthorParams struct {
    Name string      `db:"name" json:"name"`
    Bio  pgtype.Text `db:"bio" json:"bio"`
}

func (q *Queries) CreateAuthor(ctx context.Context, arg CreateAuthorParams) (Author, error) {
    row := q.db.QueryRow(ctx, createAuthor, arg.Name, arg.Bio)
    var i Author
    err := row.Scan(&i.ID, &i.Name, &i.Bio)
    return i, err
}

So it should provide a similar experience to using a query builder: You can write things that are close to SQL queries and have the types mapped
automatically

Usage of pgx

There's even more complex query that neither query builder nor sqlc can handle. This is where you can use pgx to handle these specific complex query.

pgx also comes with plenty of useful tools which made it easier to
write raw SQL:

1. Named argument & collect rows:

Named arguments (@id, @name, @description...) as placeholder instead of positional placeholder ($1, $2, $3...): pgx.NamedArgs
Collect rows to array of struct using helper function instead of scanning manually: pgx.RowToStructByName

Insert with named argument

type Author struct {
    Id   int         `db:"id"`
    Name string      `db:"name"`
    Bio  pgtype.Text `db:"bio"`
}

func pgxInsert(db *database.Database, name string, bio pgtype.Text) (Author, error) {
    // use named arguments instead $1, $2, $3...
    query := `INSERT INTO author (name, bio) VALUES (@name, @bio) RETURNING *`
    args := pgx.NamedArgs{
        "name": name,
        "bio":  bio,
    }
    rows, err := db.Pool.Query(context.Background(), query, args)
    if err != nil {
        return Author{}, nil
    }
    defer rows.Close()

    // use collect helper function instead of scanning rows
    return pgx.CollectOneRow(rows, pgx.RowToStructByName[Author])
}

Select and collect one row

func pgxSelect(db *database.Database, id int) (Author, error) {
    // notice that I dont select id
    // and use RowToStructByNameLax to allows some of the column missing
    query := `SELECT name, bio from author where id = @id`
    args := pgx.NamedArgs{
        "id": id,
    }

    rows, err := db.Pool.Query(context.Background(), query, args)
    if err != nil {
        return Author{}, err
    }
    defer rows.Close()

    return pgx.CollectOneRow(rows, pgx.RowToStructByNameLax[Author])
}

Select, collect and append to slice

func pgxSelectAllId(db *database.Database) ([]int, error) {
    query := `SELECT id from author`

    rows, err := db.Pool.Query(context.Background(), query)
    if err != nil {
        return []int{}, err
    }
    defer rows.Close()

    // use this if you dont need appending to slice
    // idArr, err := pgx.CollectRows(rows, pgx.RowTo[int])
    idArr := []int{}
    idArr, err = pgx.AppendRows(idArr, rows, pgx.RowTo[int])
    if err != nil {
        return []int{}, err
    }

    return idArr, nil
}

2. Bulk insert with Postgres's COPY:

func pgxCopyInsert(db *database.Database, authors []Author) (int64, error) {
    rows := [][]any{}
    columns := []string{"name", "bio"}
    tableName := "author"

    for _, author := range authors {
        rows = append(rows, []any{author.Name, author.Bio})
    }

    return db.Pool.CopyFrom(
        context.Background(),
        pgx.Identifier{tableName},
        columns,
        pgx.CopyFromRows(rows),
    )
}

Examples can be found here: Github repo

Summary

In a typical Golang project I will use:

sqlc for CRUD operation and simple query.
pgx for some specific complex query that sqlc can't parse.

Pgx and sqlc tutorial

Source code of this tutorial can be found here: Github repo

1. Add pgx and install sqlc

You will use sqlc as a cli tool for generating go codes, please install
sqlc using this following guide from official docs: install sqlc

Add pgx package to your Go module

go get github.com/jackc/pgx/v5

2. Create a directory to store query and schema files.

./sqlc/schema.sql

CREATE TABLE author (
    id   SERIAL PRIMARY KEY,
    name VARCHAR(100) NOT NULL UNIQUE,
    bio  TEXT
);

./sqlc/query.sql

-- name: GetAuthor :one
SELECT *
FROM author
WHERE id = $1
LIMIT 1;

-- name: ListAuthors :many
SELECT *
FROM author
ORDER BY name;

-- name: CreateAuthor :one
INSERT INTO author (name, bio)
VALUES (lower(@name), @bio)
RETURNING *;

3. Create sqlc config and generate code:

sqlc.yaml at project's root

version: "2"
sql:
  - engine: "postgresql"
    queries: "sqlc/query.sql"
    schema: "sqlc/schema.sql"
    gen:
      go:
        package: "sqlc" # Package name
        out: "database/sqlc" # Output folder
        sql_package: "pgx/v5" # Use sql types provided by pgx
        emit_json_tags: true
        emit_db_tags: true # this helps pgx scan struct using types generated by sqlc

Run this command to generate code:

sqlc generate

Check the files generated by sqlc:

4. Create a database package to wrap pgx and sqlc

./database/database.go

package database

import (
    "context"
    "log"

    "github.com/jackc/pgx/v5/pgxpool"
    "github.com/remvn/go-pgx-sqlc/database/sqlc"
)

type Database struct {
    Pool  *pgxpool.Pool
    Query *sqlc.Queries
}

func NewDatabase(connStr string) *Database {
    // this only create pgxpool struct, you may need to ping the database to
    // grab a connection and check availability
    pool, err := pgxpool.New(context.Background(), connStr)
    if err != nil {
        log.Fatal(err)
    }

    // this is generated by sqlc cli
    query := sqlc.New(pool)

    database := Database{
        Pool:  pool,
        Query: query,
    }
    return &database
}

5. Pgx and sqlc in action

Please check out this code: database_test.go

If you have docker installed, clone the repo and run this command:

go test -v ./...

With the implementation of testcontainer for go, it will create a postgres container on the fly and run integration test on that database!

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