How to connect a Go application to a database

test_connect/go.mod

@@ -0,0 +1,14 @@
+module test_connect
+
+go 1.22.5
+
+require github.com/jackc/pgx/v5 v5.6.0
+
+require (
+	github.com/jackc/pgpassfile v1.0.0 // indirect
+	github.com/jackc/pgservicefile v0.0.0-20221227161230-091c0ba34f0a // indirect
+	github.com/jackc/puddle/v2 v2.2.1 // indirect
+	golang.org/x/crypto v0.25.0 // indirect
+	golang.org/x/sync v0.7.0 // indirect
+	golang.org/x/text v0.16.0 // indirect
+)

test_connect/go.sum

@@ -0,0 +1,28 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/jackc/pgpassfile v1.0.0 h1:/6Hmqy13Ss2zCq62VdNG8tM1wchn8zjSGOBJ6icpsIM=
+github.com/jackc/pgpassfile v1.0.0/go.mod h1:CEx0iS5ambNFdcRtxPj5JhEz+xB6uRky5eyVu/W2HEg=
+github.com/jackc/pgservicefile v0.0.0-20221227161230-091c0ba34f0a h1:bbPeKD0xmW/Y25WS6cokEszi5g+S0QxI/d45PkRi7Nk=
+github.com/jackc/pgservicefile v0.0.0-20221227161230-091c0ba34f0a/go.mod h1:5TJZWKEWniPve33vlWYSoGYefn3gLQRzjfDlhSJ9ZKM=
+github.com/jackc/pgx/v5 v5.6.0 h1:SWJzexBzPL5jb0GEsrPMLIsi/3jOo7RHlzTjcAeDrPY=
+github.com/jackc/pgx/v5 v5.6.0/go.mod h1:DNZ/vlrUnhWCoFGxHAG8U2ljioxukquj7utPDgtQdTw=
+github.com/jackc/puddle/v2 v2.2.1 h1:RhxXJtFG022u4ibrCSMSiu5aOq1i77R3OHKNJj77OAk=
+github.com/jackc/puddle/v2 v2.2.1/go.mod h1:vriiEXHvEE654aYKXXjOvZM39qJ0q+azkZFrfEOc3H4=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
+github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
+golang.org/x/crypto v0.25.0 h1:ypSNr+bnYL2YhwoMt2zPxHFmbAN1KZs/njMG3hxUp30=
+golang.org/x/crypto v0.25.0/go.mod h1:T+wALwcMOSE0kXgUAnPAHqTLW+XHgcELELW8VaDgm/M=
+golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
+golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/text v0.16.0 h1:a94ExnEXNtEwYLGJSIUxnWoxoRz/ZcCsV63ROupILh4=
+golang.org/x/text v0.16.0/go.mod h1:GhwF1Be+LQoKShO3cGOHzqOgRrGaYc9AvblQOmPVHnI=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

test_connect/main.go

@@ -0,0 +1,123 @@
+package main
+
+import (
+	"database/sql"
+	"fmt"
+	"log"
+	"os"
+
+	_ "github.com/jackc/pgx/v5/stdlib"
+)
+
+func main() {
+	// connect to a database
+	conn, err := sql.Open("pgx", fmt.Sprintf("host=localhost port=5432 dbname=test_connect user=%s password=%s", os.Getenv("PGUSER"), os.Getenv("PGPWD")))
+	if err != nil {
+		log.Fatalf("Unable to connect to the database: %v\n", err)
+	}
+	defer conn.Close()
+
+	log.Println("Connected to database!")
+
+	// test my connection
+	err = conn.Ping()
+	if err != nil {
+		log.Fatal("Cannot ping database!")
+	}
+
+	log.Println("Pinged database!")
+
+	// get rows from table
+	err = getAllRows(conn)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// insert a row
+	query := `insert into users (first_name, last_name) values ($1, $2)`
+	_, err = conn.Exec(query, "Jack", "Brown")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	log.Println("Inserted a row!")
+
+	// get rows from table again
+	err = getAllRows(conn)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// update a row
+	stmt := `update users set first_name = $1 where first_name = $2`
+	_, err = conn.Exec(stmt, "Jackie", "Jack")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	log.Println("Updated one or more rows")
+
+	// get rows from table again
+	err = getAllRows(conn)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// get one row by id
+	var firstName, lastName string
+	var id int
+
+	query = `select id, first_name, last_name from users where id = $1`
+	row := conn.QueryRow(query, 1)
+
+	err = row.Scan(&id, &firstName, &lastName)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	log.Println("Query row returns", id, firstName, lastName)
+
+	// delete a row
+	query = `delete from users where id = $1`
+	_, err = conn.Exec(query, 3)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	log.Println("Delete a row")
+
+	// get rows again
+	err = getAllRows(conn)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func getAllRows(conn *sql.DB) error {
+	rows, err := conn.Query("select id, first_name, last_name from users")
+	if err != nil {
+		log.Println(err)
+		return err
+	}
+	defer rows.Close() // IMPORTANT!!
+
+	var firstName, lastName string
+	var id int
+
+	for rows.Next() {
+		err := rows.Scan(&id, &firstName, &lastName)
+		if err != nil {
+			log.Println(err)
+			return err
+		}
+		fmt.Println("Record is", id, firstName, lastName)
+	}
+
+	if err = rows.Err(); err != nil {
+		log.Fatalf("Error scanning rows: %v", err)
+	}
+
+	fmt.Println("----------------------------")
+
+	return nil
+}